Sandhill Restoration Studies and Experimental Introduction of ......Sandhill Restoration Studies and...

Sandhill Restoration Studies and Experimental Introduction of Ziziphus celata at Lake Wales

Ridge National Wildlife Refuge

FINAL REPORT

Eric S. MengesCarl W. WeekleyGretel L. Clarke

2008

Florida Fish and Wildlife Conservation Commission620 South Meridian Street

Tallahassee, FL 32399-1600

Sandhill Restoration Studies and Experimental Introduction of Ziziphus celata at Lake Wales Ridge National

Wildlife Refuge


Archbold Biological StationP.O. Box 2057

Lake Placid, FL 33862

Submitted as final report forFlorida Fish and Wildlife Conservation Commission

Project NG02-002

2008

This report is the result of a project supported by the Florida Fish and Wildlife Conservation Commission’s Nongame Wildlife Trust Fund. It has been reviewed for clarity, style, and typographical errors, but has not received peer review. Any opinions or recommendations in this report are those of the authors and do not represent policy of the Commission.

Suggested citation:

Menges, E. S., C. W. Weekley, and G. L. Clarke. 2008. Sandhill restoration studies and experimental introduction of Ziziphus celata at Lake Wales Ridge National Wildlife Refuge. Final report. Florida Fish and Wildlife Conservation Commission, Tallahassee, Florida, USA. Available from <http://research.myfwc.com/publications/>.

This Agency does not allow discrimination by race, color, nationality, sex, or handicap. If you believe you have been discriminated against in any program, activity or facility of this agency, write to Florida Fish and Wildlife Conservation Commission, 620 S. Meridian St., Tallahassee, FL 32399-1600, or to Office for Human Relations, USFWS, Dept. of Interior, Washington, D.C. 20240.

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Sandhill Restoration Studies and Experimental Introduction of Ziziphus celata at Lake Wales Ridge

National Wildlife Refuge


Archbold Biological Station, P.O. Box 2057, Lake Placid, FL 33862

Abstract: Restoration of degraded habitat and recovery of imperiled species are 2 of the main challenges facing land managers in Florida. To investigate the restoration dynamics of a long-unburned Lake Wales Ridge sandhill, we compared the effects of prescribed fire with (saw-and-burn treatment) and without (burn-only treatment) prior felling of the oak subcanopy to an untreated control in a 7-year study. Restoration goals included retaining canopy pines, reducing subcanopy and shrub layers, creating more bare sand, increasing herb diversity and abundance, and maintaining rare species populations. We collected data on sandhill community responses, performance of a population of the narrowly endemic Florida ziziphus (Ziziphus celata) introduced after treatments, and demography of 2 endemic plants, scrub buckwheat (Eriogonum longifolium var. gnaphalifolium) and scrub plum (Prunus geniculata). Longleaf pine (Pinus palustris) survival was lowest in the saw-and-burn treatment, intermediate in burn-only, and highest in the control. Survival increased with distance from the center of the enhanced fuel zone of the saw-and-burn treatment. The oak subcanopy was eliminated by the saw-and-burn treatment and reduced with burn-only. Shrub stem densities decreased temporarily, but then increased in both burn treatments. Both treatments (but especially saw-and-burn) increased bare sand, but had limited effects on herbaceous plants and graminoids. Although the treatments altered the structure of the sandhill community, species composition was not dramatically changed. Five years post-introduction, Florida ziziphus transplant survival was greater than 75%. Contrary to expectation, transplant survival was greater in the control than in the saw-and-burn treatment. Introduced plants have not grown since the introduction. Florida ziziphus seed germination was less than 5% and seedling survival less than 10%. Scrub buckwheat responded positively to the burn treatments, with high survival in all treatments and increased initial growth, flowering, and seedling recruitment in the burn-only and, especially, the saw-and-burn treatments. Likewise, scrub plum had high survival in all treatments, although severely burned, fire-consumed plants were more likely to die. Fire benefits scrub plum by increasing flowering 2–3 years after fire. The results of our 7-year study of the restoration dynamics of a long-unburned Lake Wales Ridge sandhill indicate that chainsaw felling of the subcanopy can be useful as a preburn treatment to increase fire coverage, and is beneficial in increasing bare sand and favoring demographic responses of some species. However, high fire intensities in areas with felled fuels can result in higher longleaf pine mortality. Florida ziziphus transplants into postburn sites were hampered by rapid shrub resprouting in the saw-and-burn treatment. The saw-and-burn pre-treatment can be useful in “speeding up” restoration, but care should be taken to avoid high fire intensities, especially near longleaf pines. The ultimate goal of sandhill restoration should be the return of a frequent low-intensity fire regime.

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ACKNOWLEDGMENTS

We gratefully acknowledge the various contributions of the following individuals: Kim Adams, Mandy Brothers, Laura Calabrese, Martha Ellis, Orou Gaoue, April Hansgate, Betsey Hermanson, Becky Hewitt, Sarah Hicks, Tracy Hmielowski, Tania Kim, Heather Lindon, Molly Mathias, David Matlaga, Courtney McCusker, Dorothy Mundell, Jennifer Navarra, Steph Neimeister, Ian Pfingstein, Beth Richards, Marcia Rickey, Sonali Saha, Jenny Schafer, Theresa Strazisar, Katie Stuble, Matt Trager, Hadiya White, David Zaya, and Robin Zinthefer. Pedro Quintana-Ascencio and Marcia Rickey provided valuable assistance on data analysis. We thank Fred Adrian and Dorn Whitmore of the U.S. Fish and Wildlife Service, Adam Peterson and Steve Morrison from The Nature Conservancy, and their respective staffs for the management treatments that made our research possible. We also thank Dorothy Brazis and Kay Maddox of Historic Bok Sanctuary for assistance in the Florida ziziphus introduction. The report was improved by the comments of one anonymous reviewer and the editorial assistance of Cavell Kyser. Finally, we thank the Florida Fish and Wildlife Conservation Commission’s Nongame Wildlife Trust Fund for financial support.

FLORIDA FISH AND WILDLIFE CONSERVATION COMMISSION FINAL REPORT

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SANDHILL RESTORATION—Menges et al.

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TABLE OF CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The Problem: Sandhill Restoration and Listed Species Recovery. . . . . . . . . . . 1 Relevance of Project to Nongame Conservation . . . . . . . . . . . . . . . . . . . . . . . . 2 Previous Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Study Site and Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 The Sandhill Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Florida Ziziphus Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Scrub Buckwheat Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Scrub Plum Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Sandhill Community Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Florida Ziziphus Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Scrub Buckwheat Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Scrub Plum Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Sandhill Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Florida Ziziphus Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Scrub Buckwheat Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Scrub Plum Demography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

MANAGEMENT IMPLICATIONS AND RECOMMENDATIONS . . . . . . . . 56

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Appendix A. Species list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

SANDHILL RESTORATION—Menges et al. 1

INTRODUCTION

The Problem: Sandhill Restoration and Listed Species Recovery

Longleaf-pine (Pinus palustris)-wiregrass (Aristida stricta var. beyrichiana) ecosystems were once predominant across the southeastern United States, supporting hundreds of rare and endemic species (Hardin and White 1989, Sorrie and Weakley 2006) and exceptionally high ground-layer species diversity (Kirkman et al. 2001, 2004). (See Appendix A for scientific names of species mentioned in this report.) These ecosystems, including xeric sandhills, have undergone a catastrophic decline over the past 150 years due to logging, conversion to other uses, and fire suppression, with less than 5% of their original acreage remaining (Platt 1999, Outcalt and Sheffield 1996, Van Lear et al. 2005). Old-growth longleaf pine stands are even rarer (Varner and Kush 2004). Restoration of these ecosystems has been an important conservation goal for many years (Outcalt et al. 1999, Mulligan et al. 2002).

On Florida’s Lake Wales Ridge, sandhill ecosystems have a larger shrub component and fewer species than more northern sandhills (Abrahamson et al. 1984) and, like their northern counterparts, have been largely converted to other uses. The few hundred acres of remaining sandhill on the Lake Wales Ridge are generally degraded due to a history of logging, fragmentation, and fire-suppression (Peroni and Abrahamson 1986). Lake Wales Ridge sandhills provide habitat for dozens of state or federally listed species (Enge 1995). These include the gopher tortoise (Gopherus polyphemus) and its many commensal invertebrates and reptiles (Schwartz and Karl 2005). In addition, over a dozen federally listed endemic plants preferentially or frequently occur in Ridge sandhills. Sandhill restoration projects must consider the needs of individual species as well as ecosystem structure and function.

One species that depends on sandhill ecosystems is Florida ziziphus (Ziziphus celata), one of the most highly endangered plants in Florida. Known from only a dozen sites in Polk and Highlands counties, most populations occur in privately owned pastures that were formerly sandhill (Weekley et al. 1999). Loss and fragmentation of habitat have resulted in genetically depauperate populations incapable of sexual reproduction (Weekley et al. 2002). Recovery of Florida ziziphus requires the establishment of genetically diverse populations capable of producing viable seeds. The main means to accomplish this goal is the creation of new populations on publicly protected sites containing appropriate habitat.

Many other listed species occur in sandhills on the Lake Wales Ridge. These include species that occur primarily in sandhill (e.g., Lewton’s milkwort

FLORIDA FISH AND WILDLIFE CONSERVATION COMMISSION FINAL REPORT2

[Polygala lewtonii]) and species that occur in both sandhill and scrub (e.g., Britton’s beargrass [Nolina brittoniana]). Two listed species that occur in both scrub and sandhill are scrub buckwheat (Eriogonum longifolium var. gnaphalifolium) and scrub plum (Prunus geniculata). Research on the demography and fire ecology of these species is critical to their effective management and recovery.

In this project, we evaluated experimental imposition of treatments to restore a long-unburned sandhill site. In addition, we implemented a large experimental introduction of Florida ziziphus and assessed the impact of management treatments on the success of the introduction. Finally, within the context of the treatments, we studied the post-treatment demography of scrub buckwheat and scrub plum. We received funding from the Florida Fish and Wildlife Conservation Commission’s Nongame Wildlife Trust Fund for work done from April 2004 through May 2007. For the sake of a comprehensive report, here we summarize the results of our research for the period 2001 through mid-2007.

Relevance of Project to Nongame Conservation

Restoration of fire-suppressed sandhills will benefit both wildlife and plants that live in or utilize this ecosystem. The research results presented here are relevant to Florida Fish and Wildlife Conservation Commission land managers responsible for the restoration of several hundred acres of sandhill encompassed by the Lake Wales Ridge Wildlife and Environmental Area and for the recovery of state and federally listed plants and animals that occur there. What we learn about the effects of pre-fire felling of the subcanopy is relevant to other land managers who are evaluating the use of alternative treatments for the restoration and maintenance of upland Florida ecosystems.

Previous Work

Sandhill Restoration.—Longleaf pine is a long-lived species with well-known adaptations to frequent, low intensity fire (Platt et al. 1988, Platt 1999). Fire suppression of remnant longleaf pine-wiregrass sandhills has resulted in degradation of these habitats and loss of biodiversity. In addition, dense hardwoods suppress longleaf pine recruitment in long-unburned sites (Gilliam and Platt 1999). In Florida, fire suppression results in the invasion of sandhill by scrub oaks (Myers 1985, Myers and White 1987). Many more examples of the effects of fire suppression on longleaf pine-wiregrass ecosystems could be listed. Across the southeast, restoration of fire-suppressed longleaf pine-wiregrass ecosystems is one of the main challenges facing land managers.


In restoring sandhill habitat, land managers seek to employ techniques that promote the survival and recruitment of longleaf pines (e.g., U.S. Fish and Wildlife Service [USFWS] 1999), decrease the importance of woody plants in the subcanopy and shrub layers, and increase coverage of herbaceous plants, especially fire-carrying graminoids such as wiregrass. The reintroduction of fire can benefit sandhill ecosystems by increasing herbaceous coverage, including increasing wiregrass abundance (Reinhart and Menges 2004). However, fire alone will not necessarily reduce shrub stem densities in longleaf pine systems (Olson and Platt 1995); much depends on the season of burn and fire intensities (Glitzenstein et al. 1995, Drewa et al. 2002). Long-unburned sites (Gibson et al. 1990) and stands with heavier fuels (Thaxton and Platt 2006) will burn with higher fire temperatures, which may reduce shrub resprouting or increase longleaf pine mortality (Varner et al. 2005).

A variety of sandhill restoration techniques that do not use fire or are combined with fire have been tested in recent years. These approaches are intended to have direct effects on herbaceous species and pine recruitment, as well as facilitate the use of fire. For example, in Alabama, burning and hardwood removal increased longleaf pine seedling establishment in a fire-suppressed stand (Kush et al. 2004). In Florida, prescribed fire alone or combined with herbicide and mechanical treatments helped move longleaf pine sandhills closer to reference conditions (Provencher et al. 2001a,b; Brockway et al. 2005). Extensive planting of longleaf pine, combined with burning, has helped restore stands where longleaf pine has been logged out (Seamon 1998). Herbicides have been used to suppress oaks in sandhill areas that could not be burned (Wilkins et al. 1993, Brockway et al. 1998, Brockway and Outcalt 2000). However, no previous study has targeted the endemic-rich Lake Wales Ridge sandhill ecosystem, even though land managers have begun to explore various mechanical methods as alternatives or pre-treatments for prescribed fire.

Biology and Conservation of Florida Ziziphus.—Florida ziziphus is one of the rarest (Ward et al. 2003) and most imperiled (USFWS 1999; Coile and Garland 2003; Turner et al. 2006a,b) plants in Florida. It is known from 12 sites in Polk and Highlands counties, only 2 of which are publicly protected. All populations occur on xeric yellow sands that historically supported Florida sandhill, but today most sites have been converted to pasture.

Florida ziziphus is a multi-stemmed clonal shrub to 2 m in height. It is self-incompatible (Weekley and Race 2001) and genetically depauperate (Godt et al. 1997, Weekley et al. 2002). The 12 confirmed wild genotypes (Weekley et al. 2007b) belong to just 2 cross-compatible mating types. Most populations are uniclonal and, due to its self-incompatibility system and the


distance between populations, incapable of producing viable fruits. An ex situ population at Historic Bok Sanctuary, comprising several genotypes of both mating types, generally produces substantial seed crops annually. Seeds and seedlings obtained from the Bok population have provided propagules for the genetic augmentation of publicly protected wild populations and for the experimental creation of new populations (Weekley and Menges 2006).

In the absence of sexual reproduction, most wild Florida ziziphus populations persist through vegetative spread (Weekley and Menges 2006). However, Ellis et al. (2007) found that population projections based on demographic data predicted long-term population declines, despite episodic clonal recruitment. Thus, even protected populations may be doomed to extinction in the absence of genetic augmentations to ensure sexual reproduction. However, most populations are not protected and survive at the sufferance of private landowners. Recovery of Florida ziziphus therefore depends on creating viable populations on protected sites.

The U.S. Fish and Wildlife Service Recovery Plan for Florida ziziphus (USFWS 1999) mandates the establishment of new populations on conservation lands within its documented historical range (Species-level Recovery Action S2.5.3). Because decades of fire suppression have resulted in the degradation of Lake Wales Ridge sandhills, the recovery plan also recommends that prescribed fire be used to prepare and maintain appropriate habitat for introduced populations (Habitat-level Recovery Actions H1.2.1 and H2.1, H3). We chose the Lake Wales Ridge National Wildlife Refuge’s Carter Creek sandhill for an experimental introduction because it meets the recovery plan’s criteria (appropriate, protected site within the historical range) and because the managing agency (the USFWS) was willing to apply prescribed fire to the site in preparation for the introduction.

Imposition of the Saw and Burn restoration treatments at Carter Creek afforded an opportunity to compare the demographic performance of Florida ziziphus transplants and seedlings under different microhabitat conditions. We expected that the burn-only and saw-and-burn treatments would reduce subcanopy, shrub, and litter cover relative to the control, and we hypothesized that the more open conditions provided by these treatments would promote the survival and growth of transplants and seedlings.

Biology and Conservation of Scrub Buckwheat—Scrub buckwheat, a Florida endemic, is state and federally listed as threatened (Coile and Garland 2003, USFWS 1999). This perennial herb is resilient to fire, resprouting and flowering after burns (McConnell and Menges 2002). Although scrub buckwheat can persist with a variety of fire return intervals, periodic fires


promote population viability (Satterthwaite et al. 2002). Mechanical pre-treatments for fire could also be important in managing for scrub buckwheat but, prior to this project, had not been examined. The potential of harmfully increased fire intensities in mechanically treated areas or alterations in litter dynamics (which could suppress seedling recruitment) required evaluation. To address the effects of mechanical pre-treatment on scrub buckwheat, we studied its response in the Carter Creek Saw and Burn experiment.

Biology and Conservation of Scrub Plum.—Scrub plum, a multi-stemmed but nonclonal shrub endemic to the Lake Wales Ridge (Ward 1979, Kral 1983, USFWS 1999), is a state (Coile and Garland 2003) and federally listed endangered species (USFWS 1999). It is an edaphic generalist, occurring in rosemary and oak scrub, scrubby flatwoods, and sandhills (USFWS 1999, Weekley and Menges 2001). Scrub plum is andromonoecious (having both male and bisexual flowers on the same plant) (Weekley and Menges 2002), a rare breeding system documented for only 2% of all angiosperms (Richards 1997). Despite its relatively wide distribution on the Lake Wales Ridge, scrub plum has been monitored at only 2 sites over the last decade, and there are no published studies of its biology, autecology, or demography. U.S. Fish and Wildlife Service recovery objectives for scrub plum include monitoring of existing populations, research on its life history traits, development of a quantitative description of its population structure, and assessment of its management requirements (USFWS 1999).

While scrub plum persists on long-unburned sites, most sexual reproduction takes place in the years immediately following fire. However, even in populations with an apparent abundance of flowering and fruiting plants, seedling recruitment is rarely observed (USFWS 1999). From earlier studies we know that scrub plum typically resprouts vigorously following fire (Weekley 1997; Weekley and Menges 2003a,b), but there are no prior large-scale studies comparing the demographic performance of burned and unburned plants.

In this report, we analyze the postburn recovery of scrub plum plants based on the Saw and Burn Project (2001–2007).

Project Objectives

The Carter Creek Sandhill Restoration Project addresses 2 key issues important to land managers in Florida: habitat restoration and the recovery of endangered species. Our approach in this project was to conduct an intensive study of sandhill restoration, to carry out an experimental introduction of Florida ziziphus, and to investigate the fire ecology and post-treatment


demography of 2 imperiled and endemic plants. The specific goals of this project were to

1. study the restoration of a long-unburned Lake Wales Ridge sandhill ecosystem at the Lake Wales Ridge National Wildlife Refuge/Carter Creek;

2. conduct research on the establishment of a viable population of Florida ziziphus on a sandhill site undergoing restoration;

3. study the postfire population dynamics of scrub buckwheat; and4. study the postfire population dynamics of scrub plum.

The sandhill restoration study used prescribed fire with and without prior felling of the oak subcanopy (referred to as the saw-and-burn and burn-only treatments, respectively) to compare vegetation responses to an untreated control. Sandhill community sampling included pre- and post-treatment surveys of longleaf pine, the key canopy tree within the sandhill community (Myers 1990), and detailed annual sampling of community plots for vegetation structure and composition.

The Florida ziziphus study introduced propagules (potted 2- to 3-year-old seedlings and seeds) into a range of post-treatment microhabitats, from which we expect to establish a self-perpetuating population and to learn more about the ecological requirements and population dynamics of one of Florida’s rarest and most endangered species. The Carter Creek introduction was designed as an experiment to address 2 questions central to the recovery of Florida ziziphus. First, is the translocation of potted plants more effective than sowing seeds in establishing a new population? Second, what microhabitat conditions best promote the survival of introduced transplants and the germination of seeds?

Our demography studies (sensu Menges and Gordon 1996) of scrub buckwheat and scrub plum provide data on how fire affects the survival, growth, fecundity, and recruitment of these rare sandhill endemics. For both species, we followed tagged and mapped plants in annual censuses conducted during their peak flowering seasons and documented seedling recruitment.


METHODS

Study Site and Treatments

This project was carried out on the Carter Creek Tract of the Lake Wales Ridge National Wildlife Refuge (Highlands County), which is managed by the USFWS. In spring 2001, we established 12 management units within the Carter Creek sandhill, and within each management unit we set up 6 circular 5-m-radius community sampling plots (Fig. 1). Within these 72 plots we collected pre-treatment data on community structure and species composition. We flagged all longleaf pines encountered within the management units (Fig. 2). A subset of the community plots served as implantation sites for the Florida ziziphus introduction (Fig. 3). In addition, we tagged 297 scrub buckwheat plants (Fig. 4) and 903 scrub plum shrubs (Fig. 5) and collected pre-treatment demographic data. Using a Trimble Pro-XR Global Positioning System (GPS), we mapped the 72 community plots and all plants (longleaf pines, scrub plums) or plots (scrub buckwheat) marked for monitoring.

Fig. 1. Location of management units and community plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.


Fig. 2. Distribution of longleaf pines in 12 management units at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.

Fig. 3. Distribution of Florida ziziphus introduction plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.


Fig. 4. Distribution of scrub buckwheat plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.

Fig. 5. Distribution of scrub plum plants at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.


We applied 3 treatments (burn-only, subcanopy felling followed by burning [saw-and-burn], and an untreated control) to each of 4 management units. Prior to the burn, we used chainsaws to fell oaks and other subcanopy trees (except for longleaf pines) in a 15-m “fuel-enhancement zone” centered on each of the 24 community plots within the saw-and-burn treatment area. Subcanopy felling and the prescribed burn were conducted in the spring and summer of 2001 with help from the Archbold Biological Station Maintenance Department, The Nature Conservancy, the USFWS, and the Florida Division of Forestry. The translocation of Florida ziziphus propagules was carried out in June 2002 by Archbold and Historic Bok Sanctuary.

The Sandhill Community

Community Sampling.—We collected pre-treatment vegetation data in April 2001 and post-treatment data annually in April thereafter through 2005. In 2001, we sampled species composition and community structure (Table 1) within each of 72 5-m radius circular plots (Fig. 6) distributed throughout the management units (Fig. 1). However, because 11 burn-only plots were not effectively burned, they were dropped from post-treatment sampling. This left 61 community plots that were sampled annually from 2002 to 2005.

Within each community plot we collected data on 5 vegetation strata: canopy, subcanopy, shrubs, herb layer, and ground cover (lichens, litter, and bare ground). Within the 5-m-radius plot (Fig. 6), we compiled a list of all

Table 1. Overview of sampling strategy for 5 components of sandhill restoration project at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007: saw-and-burn experiment, longleaf pine survival, Florida ziziphus experimental introduction, and postfire demography of scrub buckwheat and scrub plum.

SampleComponent Sampling frequency Sampling unit size Methods

Saw-and-burn Annual 5-m-radius 61 Counts for tree, shrub, experiment community plot and herb abundance; %

cover for lichens, litter, and bare sand

Longleaf pine Infrequent Tagged individuals 228 Census for survival survivalFlorida ziziphus Quarterly through July Tagged individuals 144 plants, Level 3 monitoringa; introduction 2005, then annually 1,728 seeds microhabitat analysisScrub buckwheat Annual Tagged individuals 297 Level 3 monitoring demographyScrub plum Annual Tagged individuals 898 Level 3 monitoring demography

aDemographic monitoring sensu Menges and Gordon (1996) whereby data on recruitment, survival, growth, and fecundity of marked individuals are collected at regular intervals.


vascular plants and ground lichens and counted stems of all canopy (>8 m in height) and subcanopy (3–8 m in height) trees. We classified longleaf pines into 4 categories: grass stage, and stems <0.5 m, 0.5–3.0 m, or >3 m tall. We recorded the number of shrub stems (woody stems 0.5–3.0 m in height) by species along 4 1-x-4–m belt transects running in cardinal directions from the plot center. We counted stems of herbaceous and woody species <0.5 m tall within 8 0.25-cm-radius circular “herb” quadrats located at 2 and 4 m from the plot center in the northeast, southeast, southwest, and northwest quadrants. Within these 8 quadrats we also estimated the cover (to nearest 10%) of herbs, graminoids, and terrestrial lichens (the last 2 by species), as well as litter and bare ground.

We summarized abundance data at the level of the community plot for canopy, subcanopy, shrub, and herb species based on stem counts (converted to densities). For graminoid species, bare sand, and lichen cover, we calculated mean percent cover. For species, particularly graminoids, that were difficult to distinguish based on vegetative characters, we created species groups. We recognized species groups for the following genera: Andropogon, Aristida

Fig. 6. Schematic representation of sandhill community sampling and Florida ziziphus introduction plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007. The diagram shows a 5-m-radius circle where species list and subcanopy stems densities by species were recorded. Within this plot, we counted shrub stem densities by species in 4 belt transects. In addition, we used 0.25-m-radius circular quadrats to quantify the herb layer and estimate ground cover. A subset of these plots also received Florida ziziphus transplants (4) and seed arrays (2).


(with the exception of A. stricta var. beyrichiana), Asclepias, Cyperus, Dichanthelium + Panicum, Liatris, and Sisyrinchium.

Within the community plots, the density of longleaf pines, the predominant canopy species, was too low to assess the impact of treatments. Therefore, we sampled longleaf pines across the entire management area (Fig. 2). We collected data on 228 pines pre-treatment and 9 months and 33 months post-treatment, using the same size classes as in the community plots. Because we found only 2 grass-stage pines, we excluded them from the analyses below.

Statistical Analyses.—We used both univariate (ANOVAR) and multivariate repeated measures (MANOVAR) ANOVAs (SPSS Vers. 11.5, 2002) to evaluate changes in vegetation structure over time resulting from the contrasting treatments (Table 2). The univariate procedure is more powerful than the multivariate procedure, but has more restrictive assumptions (Potvin et al. 1990, von Ende 1993). We tested the data to determine if they met the assumptions of normality and sphericity (Mauchly’s test for sphericity). If the assumption of sphericity was not met, degrees of freedom were adjusted using the Huynh-Feldt or Greenhouse-Geisser estimated epsilon values (Potvin et al. 1990). For analyses with epsilon values < 0.7, we used a multivariate approach to repeated measures. To ensure that the data met the ANOVA assumptions of normality, we used frequency histograms, plots of the residuals vs. predicted values, and the Shapiro-Wilk test for normality. Data that did not meet the assumption of normality were transformed when possible (Table 2).

For the subcanopy and shrub strata, the assumption of sphericity was not met and the epsilon values were too low to permit use of the univariate repeated measures ANOVA. Therefore, we used MANOVAR for these strata. Since the Greenhouse-Geisser epsilon for herbs was > 0.7, we used the univariate ANOVAR for these 2 components of the herb stratum.

Table 2. Description of analyses and transformations needed for community analyses at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2005. MANOVAR= Multivariate repeated measures analysis of variance, ANOVAR = repeated measures analysis of variance (SPSS Vers. 11.5, 2002). NA = not applicable.

Normality SphericityVegetation layer Analysis transformation assumption met? Epsilon value

Subcanopy stems MANOVAR Square root No 0.448Shrub stems MANOVAR Natural log No 0.546Herb stems ANOVAR Natural log No 0.718Bare sand Kruskal-Wallis NA NA NALichens Kruskal-Wallis NA NA NAGraminoids Kruskal Wallis NA NA NA


Repeated Kruskal-Wallis tests were used to compare treatment effects on bare sand, graminoid, and lichen cover within years. Because the Kruskal-Wallis test does not provide for post-hoc pairwise comparisons, we performed 3 separate pairwise tests (control vs. burn-only, control vs. saw-and-burn, and burn-only vs. saw-and-burn) using a Bonferroni correction to adjust alpha (α = 0.05/n, where n is the number of tests). We compared treatments 1 year and 4 years post-treatment for graminoids and bare sand because we suspected that the response 1 year post-treatment was different than 4 years post-treatment. In contrast, for lichen cover we compared only the 4 years post-treatment because it was apparent that lichen cover did not change from one post-treatment year to the next. We used chi-square contingency tables and linear regression to evaluate the significance of postburn mortality patterns in longleaf pines.

We used nonmetric multidimensional scaling (NMS) (McCune and Grace 2002) to evaluate relationships in both structural data and species composition (presence-absence) among the 61 community plots differing by treatment (control, burn-only, saw-and-burn) and among pre-treatment plots and 1- and 4-year post-treatment plots. Structural data included canopy, subcanopy, shrub, and herb stem densities as well as herb, graminoid, litter, bare sand, and lichen cover. These data were relativized by the maximum value for each variable to prevent variables with greater maximum values playing an unduly large role in the analysis. To reduce noise in the species occurrence dataset, species occurring in ≤2 plots were dropped, leaving 71 species in the final matrix.

Ordinations show the relationship among sampling units based on multiple variables by positioning more similar units nearer to, and less similar units farther away from, each other. We chose NMS because it is well suited to ecological data, which are generally non-normal and fail the assumption of linearity required for some other ordination techniques (McCune and Grace 2002). We selected a 2-dimensional solution after using standard techniques to evaluate the tradeoff between minimizing the number of axes and minimizing distortion in the ordination (McCune and Grace 2002).

We identified multivariate outliers using a standard technique. Plots were considered outliers if their mean inter-plot distance (the mean distance to other plots in multidimensional space) was >2 standard deviations above the mean Euclidean distance between each plot and all others.

Indicator Species Analysis (ISA) is a method of evaluating the importance of a species within a given environmental context (McCune and Grace 2002). We applied ISA to compare species occurrence data among treatments (within


years) to determine if particular species or species groups were more frequent in any of the treatments in 2001 (pre-treatment) or 2005 (4 years post-treatment).

Florida Ziziphus Introduction

Following site preparation in 2001 (i.e., chainsaw felling of the subcanopy and prescribed burning), in June 2002 we introduced Florida ziziphus to 36 of the 72 community plots divided equally among the 3 saw-and-burn treatments (Fig. 3). We planted 144 2- to 3-year-old potted plants and 1,728 seeds. Each plot received 4 transplants and 48 seeds (Fig. 3); seeds were sown into 2 28-x-18–cm seed arrays, each with 24 seeds. Both transplants and seed arrays were enclosed in hardware cloth cages to prevent vertebrate herbivory or other disturbance. With the aid of the Archbold maintenance department, we installed a citrus-grove style irrigation system to provide supplemental watering as warranted by episodic summer dry spells. We attributed the death of 16 plants within the first few weeks to armadillo (Dasypus novemcintus) damage or transplant shock; these 16 plants, which were replaced with others representing the same maternal genotypes, are excluded from the analyses presented here.

Propagules used in the introduction were of known maternal genotype, having originated as seeds harvested from the ex situ population at Historic Bok Sanctuary. We used this information to configure the introduction so that each plot received transplants and seeds representing both mating types and at least 2 maternal genotypes. This arrangement maximizes the likelihood of future sexual reproduction between neighboring plants.

Following the introduction, we monitored Florida ziziphus transplants for survival (monthly for 6 months, quarterly through July 2005, and annually in January thereafter). We monitored seed arrays at 7- to 10-day intervals for 6 months, quarterly through July 2005, and annually in January thereafter, recording germination and survival of seedlings. In the annual demographic censuses, conducted in January (when most populations flower), we collected additional data on plant size and flowering status.

In the analysis below, we used survival curves to compare differences among the 3 pre-introduction treatments in Florida ziziphus transplant survival trajectories from December 2002 (6 months post-introduction) to January 2007 (the most recent census). We performed chi-square tests, with a Bonferroni corrected alpha for multiple tests, to evaluate differences among management units in transplant survival as of January 2007. To assess post-introduction growth rates among treatments, we used ANOVA to compare changes in size


of transplants measured in December 2002 (baseline) and January 2007. We performed paired t-tests to determine if transplants were significantly larger in 2007 than in 2002.

In October 2004 we collected microhabitat data. For each transplant we recorded the cover of overhanging vegetation and litter cover in 3 categories (<10%, 10–50%, >50%), and noted the presence or absence of encroaching shrubs (e.g., clonal oaks and palmettos). Percent vegetation and litter cover were based on ocular estimates within a 25-cm radius around each transplant. Encroachment was defined as the presence of other shrubs, rooted or not, within the 50-cm-diameter protective cage enclosing each transplant. Timing of the microhabitat survey coincided with a period of relatively high Florida ziziphus mortality in the burn-only and saw-and-burn management units. To evaluate the effect of microhabitat on transplant survival, we created a series of 11 non-exclusive binary logistic regression models with vegetation cover, litter cover, and encroaching shrub as the main effects. We used the corrected Akaike information criterion (AICc) (Burnham and Anderson 2002) to assess the relative support for the resulting models and model averaging to judge the strength of each variable.

Scrub Buckwheat Demography

We censused scrub buckwheat annually in June from 2001 to 2007, with an additional postburn census in December 2001. We sampled plants within 45 3-m-radius circular quadrats distributed equally among management treatments (15 per treatment). Scrub buckwheat quadrats were subjectively located adjacent to community plots (when plants occurred there) and in other areas of higher plant density. Within these quadrats, we marked and tagged all scrub buckwheat plants and recorded survival status, number of rosettes, basal diameter, number of flowering scapes, number of involucres (which subtend groups of flowers), and damage from herbivory, as collected in demographic censuses at Archbold Biological Station conducted since 1990 (Satterthwaite et al. 2002). Because scrub buckwheat plants can remain dormant for several years (Satterthwaite et al. 2002), tags marking the location of plants no longer present aboveground were monitored annually. We classified newly appearing plants as seedlings if total basal diameter was <2 cm (Satterthwaite et al. 2002).

We analyzed the effects of treatment (control, burn-only, and saw-and-burn) and burn status (burned vs. unburned, because not all plants in the burn-only treatment actually burned) on scrub buckwheat demographic responses. Response variables were survival, growth (change in rosette diameter), flowering status, number of scapes, and number of involucres. Since we could


not transform to normality the distribution of scape numbers, we compared discrete classes (1 scape vs. 2 or more scapes). Analyses used chi-square, t-tests, and 1-way ANOVA. For growth analyses, we include only plants with aboveground parts during the initial sampling. Variables were checked for normality and transformed as necessary for use in parametric analyses.

Scrub Plum Demography

In spring 2001, we tagged 898 scrub plum individuals on the Carter Creek sandhill study site and collected demographic data. Tagged individuals were distributed among the 12 management units representing the 3 sandhill restoration treatments: burn-only, saw-and-burn, and untreated control. We collected demographic data on a minimum of 65 scrub plum plants per management unit (Fig. 5). Based on the density of scrub plums in 72 randomly located community plots, we estimate that there were ~2,300 scrub plum individuals on site (57 plants/ha). Thus we sampled about 40% of the population.

Following the August 2001 prescribed burn, we censused scrub plum annually in February, its peak flowering season, from 2002 through 2007. In each census, we collected data on survival, size (height, maximum crown diameter, number of stems), and number of flowers (in log10 categories [i.e., 1–9, 10–99, 100–999, etc.]), and searched for seedlings within a 1-m radius of each tagged plant.

Pre-treatment, scrub plum plants in the control plots had significantly greater height and maximum crown diameter than plants in the burn-only and saw-and-burn treatments (Weekley and Menges 2001). Logistical constraints prevented the random assignment of treatments to management units. As a result, some of the control plants may occupy less xeric microsites than plants in management units that were burned. Consequently, for the analyses presented here we exclude plants in the control treatment and compare postburn recovery of burned plants to unburned plants within the burn-only and saw-and-burn treatments.

In the first postburn census (February 2002, 6 months after the August 2001 prescribed burn) we assigned the 567 scrub plum plants in the burn-only and saw-and-burn treatments to 1 of 4 burn severity categories (unburned, lightly scorched, heavily scorched, or consumed). Burn severity assignments were partly based on fire severity data collected within 2 weeks of the burn. Plants were scored as lightly scorched if some leaves remained unscorched; heavily scorched plants lost all leaves due to scorching; and consumed if twigs or branches were burned back (in extreme cases, stems were also consumed).


During the course of the study, 75 plants had to be excluded from analysis because they were accidentally disked during fireline maintenance (n = 10) or suffered damage by 2004 hurricane debris (n = 65). The post-treatment analyses presented here are based on 492 plants.

To evaluate burn severity (unburned, lightly scorched, heavily scorched, or consumed) by treatment (burn-only vs. saw-and-burn), we used chi-square tests. We used repeated measures ANOVAs to compare postburn changes in height, maximum crown diameter (mcd), and stem number for scrub plum plants in the 4 burn severity categories. We tested both height and mcd because correlations between the 2 metrics were relatively weak (r2 < 0.57 for 7 censuses, 2001–2007). To compare postburn changes in reproductive effort (flowering vs. non-flowering) and the proportion of plants in log10 flowering classes, we used chi-square tests. In the latter analysis, we excluded plants in the consumed category because of their smaller size and number (n = 19); we also combined the 100–999 and the ≥1,000 flowering classes into a single class (>100 flowers) to better satisfy the requirements of the chi-square procedure. For all post-hoc pairwise comparisons following nonparametric tests, we used a Bonferroni-corrected alpha (0.05/n, where n is the number of comparisons).


RESULTS

Sandhill Community Dynamics

Longleaf Pines.—Nearly all pines burned in the burn-only (96%) and saw-and-burn (99%) treatments, as evidenced by consumption or scorching of needles on pines in the smallest size-classes and by trunk scorching on larger pines. Mortality of unburned longleaf pines was non-existent or negligible across the 3 treatments (Fig. 7), while mortality of burned pines differed significantly between the burn-only and the saw-and-burn treatments (χ2 = 7.950, df = 1, P = 0.007). Overall, the survival rate of burned pines was higher (76.1%; 54/71) in the burn-only treatment than in the saw-and-burn treatment (54.2%; 45/83) (Fig. 7). This was also true for each size class; survival was higher in the burn-only treatment (<3 m = 39%, 3–8 m = 77%, >8 m = 89%) than in the saw-and-burn treatment (<3 m = 25%, 3–8 m = 50%, >8 m = 69%), but the difference was only significant for pines >8 m in height (for stems <3 m: χ2 = 0.676, df = 1, P = 0.411; 3–8 m: χ2 = 3.237, df = 1, P = 0.072; >8 m: χ2 = 4.629, df = 1, P = 0.031). Regardless of treatment, larger pines were less likely to be killed by fire (χ2 = 33.944, df = 2, P < 0.001).

Fig. 7. Thirty-three month postfire survival of unburned and burned longleaf pines in 3 sandhill restoration treatments at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2004.


Pines within the enhanced-fuel zone (Fig. 8) suffered significantly higher mortality than those at greater distances (χ2 = 11.133, df = 2, P = 0.004). In addition, pine survival increased significantly with distance from the center of the saw-and-burn treatment plots (Wald statistic = 9.726, df = 1, P = 0.002, 67.5% classification success) (Fig. 9). Within the 15-m fuel-enhancement zone, survival was 43% for stems <3 m tall (3/7 stems), 33% for stems 3–8 m tall (4/12 stems), and 50% for stems >8 m tall (3/6 stems).

Fig. 8. Distribution of longleaf pines and fuel-enhancement zones around saw-and-burn community plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2004.


Fig. 9. Logistic regression of longleaf pine survival by distance to center of saw-and-burn plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2004. The graph compares the predicted percent survival given by the regression equation (left Y-axis and lower X-axis) with observed number of plants surviving (right Y-axis and upper X-axis).


Subcanopy Density.—The burn-only treatment reduced subcanopy density relative to the control, and the reduction persisted through the fourth post-treatment survey (Fig. 10) (since chain-sawing eliminated the subcanopy in the saw-and-burn treatment, it is excluded from this analysis). Subcanopy density differed significantly over time (Pillai’s Trace: F = 5.523, df = 4, 32, P = 0.002), and there was also a significant year * treatment interaction (Pillai’s Trace: F = 3.26, df = 4, 32, P = 0.024), indicating that densities differed between treatments over the survey period. The burn-only treatment top-killed all subcanopy myrtle oaks (Quercus myrtifolia), suggesting that it may be more susceptible to top-killing by fire than other subcanopy oak species (e.g., sand live oak [Q. geminata] or turkey oak [Q. laevis]).

Fig. 10. Densities of subcanopy stems (per m2, stem heights >3 m and ≤8 m) by treatment from 2001 (pre-treatment) to 2005 (4 years post-treatment) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Raw means (backtransformed) are shown although the analysis was done on square root transformed data.


Shrub Density.—The 2 burn treatments initially reduced shrub density compared to the control, but by the second year post-treatment, shrub stem densities had regained or surpassed pre-treatment levels (Fig. 11). Shrub density differed significantly among years (Pillai’s Trace F = 45.009, df = 4, P < 0.001), and there was also a significant year * treatment interaction (Pillai’s Trace F = 11.363, df = 8, 112, P < 0.001), indicating that treatments had a significant impact on densities over time. Resprouting subcanopy oaks removed by chainsawing or top-killed by fire contributed to increases in shrub density in the later surveys.

Fig. 11. Densities of shrub stems (per m2, shrub heights >50 cm and <3 m) by treatment from 2001 (pre-treatment) to 2005 (4 years post-treatment) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Raw means (backtransformed) are shown although the analysis was done on natural log transformed data.


Herb Density.—Post-treatment herb densities increased slightly in the burn-only and saw-and-burn treatments compared to the control (Fig. 12), and there was a significant change in herb density over time (Greenhouse-Geisser epsilon = 0.718; F = 13.521, df = 2.872, 166.550, P < 0.001). The absence of a significant year * treatment interaction (Greenhouse-Geisser epsilon = 0.718; F = 1.178, df = 5.743, 166.550, P < 0.123) reflects the increase in herb density across all treatments, including controls. There was greater variability in herb density among plots in the 2 burn treatments than in the control.

Fig. 12. Densities of herb stems (per m2) by treatment from 2001 (pre-treatment) to 2005 (4 years post-treatment) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Raw means (backtransformed) are shown although the analysis was done on natural log transformed data.


Bare Sand Cover.—Following treatments, bare sand cover increased in the burn-only and saw-and-burn treatments (Fig. 13). With the Bonferroni corrected alpha for multiple tests (n = 6, α = 0.008), bare sand cover was significantly higher in the saw-and-burn treatment than in the control in the 1-year (Kruskal-Wallis χ2 = 27.897, df = 1, P < 0.001) and 4-year (Kruskal-Wallis χ2 = 32.846, df = 1, P < 0.001) post-treatment surveys. One year after the burn-only treatment, bare sand cover was not significantly greater than in the control (Kruskal-Wallis χ2 = 5.338, df = 1, P < 0.021), but it was significantly greater after 4 years (Kruskal Wallis χ2 = 7.124, df = 1, P < 0.008).

Fig. 13. Percent bare sand cover per square meter (calculated as the mean from 8 herb quadrats within each community plot) from 2001 (pre-treatment) to 2005 (4 years post-treatment) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. The lower and upper wide bars of the boxplot represent the 25th and 75th percentiles, respectively; the solid middle bar represents the median. The lower and upper lines show the largest and smallest values that are not outliers. The circles are outliers.


Graminoid Cover.—The 2 burn treatments reduced graminoid cover in the first post-treatment year (Fig. 14). However, with the Bonferroni corrected alpha for multiple tests (n = 6, α = 0.008), graminoid cover was significantly lower only in the saw-and-burn treatment vs. the control (Kruskal-Wallis χ2 = 12.368, df = 1, P < 0.001). Four years post-treatment, graminoid cover did not differ significantly between any pair of treatments (P > 0.162 for all pairwise comparisons).

Fig. 14. Percent graminoid cover per square meter (calculated as the mean from 8 herb quadrats within each community plot) from 2001 (pre-treatment) to 2005 (4 years post-treatment) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. The lower and upper wide bars of the boxplot represent the 25th and 75th percentiles, respectively; the solid middle bar represents the median. The lower and upper lines show the largest and smallest values that are not outliers. The circles are outliers.


Lichen Cover.—Ground lichens were virtually eliminated following the burn-only and saw-and-burn treatments and had not recovered 4 years post-treatment. However, in the first year post-treatment, with the Bonferroni corrected alpha for multiple tests (n = 3, α = 0.017), lichen cover was significantly lower only for the saw-and-burn treatment vs. the control (Kruskal-Wallis χ2 = 21.964, df = 1, P < 0.001). Four years post-treatment, both burn treatments had significantly lower lichen cover than the control (burn-only vs control: Kruskal-Wallis χ2 < 7.260, df = 1, P = 0.007; saw-and-burn vs. control: Kruskal-Wallis χ2 < 23.484, df = 1, P < 0.001).

Ordinations of Community Structure.—The NMS ordinations provide an integrated analysis and graphical display of the changes in the 9 structural components (Figs.15–18). Structural characteristics were largely unaltered in control plots, but there were substantial shifts for the burn-only (Fig. 15) and saw-and-burn (Fig. 16) treatments. Pre-treatment and control plots are characterized by high subcanopy density (Fig. 17D) and high lichen cover. One-year post-treatment, burn-only (Fig. 15) and (especially) saw-and-burn plots (Fig. 16) diverged in structural components (note movement up and left in Figs. 15 and 16), with the saw-and-burn plots having very high bare sand cover (Fig. 17A). By 4 years post-treatment, burn-only plots and some saw-and-burn plots had only moderate bare sand cover with high shrub density (Fig. 17B), while retaining higher herb (Fig. 17C) and graminoid cover than control plots. None of the burned plots regained structural characteristics of the controls in the 4 years following treatments.

Species Composition.—We recorded 107 species or species groups in community plots between 2001 and 2005 (Appendix A). The predominant canopy species was longleaf pine. The hardwood subcanopy consisted of scrub hickory (Carya floridana), sand live oak, myrtle oak, and turkey oak. The shrub layer was dominated by the same suite of clonal oaks (plus Chapman’s oak [Quercus chapmanii]), palmettos (Serenoa repens and Sabal etonia), and ericads in the genus Lyonia. The herb layer was diverse; common herbaceous species included Florida Alicia (Chapmannia floridana), sand spike-moss (Selaginella arenicola), threeawn grasses (Aristida spp.), and witchgrasses (Dichanthelium spp.). In addition to our 3 study species, we recorded several rare and endemic plants, including bigflower pawpaw (Asimina obovata), pygmy fringetree (Chionanthus pygmaeus), sweetscented pigeonwings (Clitoria fragrans), Britton’s beargrass (Nolina brittoniana), Lewton’s milkwort (Polygala lewtonii), and Carter’s mustard (Warea carteri).


Fig. 15. Nonmetric multidimensional scaling (NMS) ordination of structural data for 61 plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 2001 (pre-treatment), 2002 (1 year post-treatment), and 2005 (4 years post-treatment); P = 0.004 for the 2 dimensional solution, final stress = 14.4, final instability = 0. Structural data included canopy, subcanopy, shrub, and herb stem densities as well as herb, grass, litter, bare sand, and lichen cover. Envelopes delimiting burn-only plots in 2001 (dotted line), 2002 (dashed line), and 2005 (solid line) are shown.

Fig. 16. Nonmetric multidimensional scaling (NMS) ordination of structural data for 61 plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 2001 (pre-treatment), 2002 (1 year post-treatment), and 2005 (4 years post-treatment); P = 0.004 for the 2 dimensional solution, final stress = 14.4, final instability = 0. Structural data included canopy, subcanopy, shrub, and herb stem densities as well as herb, grass, litter, bare sand, and lichen cover. Envelopes delimiting saw-and-burn plots in 2001 (dotted line), 2002 (dashed line), and 2005 (solid line) are shown.


Fig. 17. Nonmetric multidimensional scaling (NMS) ordinations of structural data for 61 community plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 2001 (pre-treatment), 2002 (1 year post-treatment), and 2005 (4 years post-treatment) for (A) bare sand cover; (B) herb density, (C) shrub stem density, and (D) subcanopy stem density. The size of symbols is proportional to the magnitude of the variable in each plot.


Ordination Analysis of Species Composition.—Species composition was similar among treatments in pre-treatment sampling and was not dramatically altered by the 2 burn treatments, as shown in the NMS ordination (Fig. 18). However, there are some notable differences in the extent and direction of change in the ordination. The saw-and-burn and burn-only plots had greater compositional change than the control plots. Herbaceous, open-site species such as Apalachicola toadflax (Linaria floridana), coastalplain nailwort (Paronychia herniariodes), sandspur (Krameria lanceolata), and pineland pinweed (Lechea sessilifolia) defined the saw-and-burn plots (upper right of Fig. 18). Control plots shifted in the opposite direction of the treated plots, and the change was smaller.

Fig. 18. Nonmetric multidimensional scaling (NMS) ordination (axes 1 and 3) showing similarities among plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, based on species occurrences within them. Plots are grouped by treatment type (control, burn-only, and saw-and-burn) and by year (2001 = pre-treatment, 2005 = 4-year post-treatment). Final stress of the ordination was 19.62, and instability was 0.0003. Species occurring in ≤2 plots were removed prior to analysis. Envelopes delimit pre-treatment (dotted lines) and 4-year post-treatment (solid lines) plots.


Indicator Species Analysis.—A few species were affected by management treatments over the 5 years of the study, as shown by indicator species analysis. Ground lichens (Cladonia and Cladina spp.) and epiphytic bromeliads (Tillandsia spp.) were virtually eliminated in both burn treatments (Table 3). These species are vulnerable to short-term extirpation by fire. Species composition over time was less dynamic for shrubs (Table 4) than for herbs (Table 5) or graminoids (Table 6). Several herb and graminoid species increased in frequency in both burn treatments, and frequently increased more in the saw-and-burn plots. For example, Apalachicola toadflax and coastalplain nailwort were absent pre-treatment in all plots, but increased in frequency to 8% in burn-only plots and to 17% and 13%, respectively, in saw-and-burn plots. Other species that increased in frequency, especially in saw-

Table 3. Results of indicator species analysis (ISA) for Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Species differing in abundance/frequency among treatments in 2001 or 2005 (comparisons made within years). Species that are significantly different (P < 0.05, adjusted with Bonferroni correction for multiple comparisons) in 2005 are denoted with an asterisk. No species were significantly different among treatments in 2001 after the Bonferroni correction. Species are ordered by increasing P-value for 2005 analysis.

2001 2005 IVa IV IV IV IV IVCommon name control burn- saw-and- P control burn- saw-and- P only burn only burn

Apalachicola toadflaxb* 0 1 48 0.001Ballmoss* 31 34 34 >0.999 60 19 0 <0.001Bigflower pawpaw 21 21 19 0.942 23 41 18 0.024Capillary hairsedge 8 7 11 >0.999 3 11 45 0.002Coastalplain honeycombhead 4 0 17 0.144 1 1 26 0.022Coastalplain nailwortb 3 6 31 0.031Cup lichen* 35 23 29 0.298 61 6 7 <0.001Evan’s reindeer lichen 6 7 14 0.591 30 3 1 0.017Garberia 4 32 0 0.006 6 32 0 0.008Lewton’s milkwort 30 1 1 0.007 30 1 4 0.024Pricklypear 29 5 6 0.063 34 8 4 0.022Reindeer lichen* 19 21 19 >0.999 66 11 0 <0.001Sand pine 17 4 4 0.291 23 5 0 0.036Scrub buckwheat 6 5 32 0.020 8 9 20 0.373Showy dawnflower 17 0 1 0.062 37 0 8 0.003Skyblue lupine 1 2 13 0.288 14 12 39 0.017Spanish moss* 32 30 32 >0.999 61 15 0 <0.001Tough bully 0 0 21 0.020 0 0 21 0.022Trailing milkvine 11 7 8 >0.999 31 10 1 0.018Virginia snakeroot 21 0 0 0.019 11 0 3 0.270Whitemouth dayflower 15 1 15 0.568 35 13 11 0.038

aIV = percent of perfect indication of the species within the set of plots defined by the treatment type and census year. bThis species was not recorded in 2001.


Table 4. Species occurrence matrix for the shrubs displaying the percentage of community plots containing each species in the pre-treatment (2001) and 1-, 2-, 3-, and 4-year post-treatment (2002–2005) surveys at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida

Treatment Shrub species 2001 2002 2003 2004 2005

Control Bigflower pawpaw 13 8 13 17 17 Chapman’s oak 21 33 50 54 63 Feay’s palafox 8 8 8 13 13 Florida sensitive brier 0 0 0 0 4 Garberia 4 4 4 4 4 Myrtle oak 50 46 50 50 63 Pigmy fringetree 4 0 0 0 0 Pricklypear 0 0 0 4 4 Sand live oak 88 100 100 100 96 Sand pine 0 0 0 0 4 Saw palmetto 88 88 88 88 88 Scrub palmetto 71 75 75 79 79 Scrub plum 13 8 8 8 8 Turkey oak 79 71 67 75 79Burn-only Bigflower pawpaw 31 23 31 31 31 Chapman’s oak 23 0 15 31 46 Feay’s palafox 23 0 15 38 31 Garberia 8 8 15 8 23 Myrtle oak 46 46 46 46 46 Pigmy fringetree 8 8 8 8 8 Pricklypear 0 0 0 8 8 Sand live oak 92 31 100 100 100 Sand pine 0 0 0 0 8 Saw palmetto 92 77 85 85 85 Scrub palmetto 92 92 92 92 92 Scrub plum 8 8 15 15 15 Turkey oak 23 23 46 54 38Saw-and-burn Bigflower pawpaw 13 4 4 4 13 Chapman’s oak 13 8 54 58 58 Feay’s palafox 4 4 13 13 13 Myrtle oak 25 4 17 21 33 Pigmy fringetree 4 0 4 4 4 Pricklypear 0 0 0 0 4 Sand live oak 92 50 100 100 100 Saw palmetto 79 58 75 79 75 Scrub palmetto 58 67 79 83 79 Scrub plum 4 0 4 4 4 Turkey oak 67 63 96 92 96


Table 5. Species occurrence matrix for non-graminoid herbs, displaying the percentage of community plots containing each species in the pre-treatment (2001) and 1-, 2-, 3-, and 4-year post-treatment (2002–2005) surveys at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida.

Treatment Herb species 2001 2002 2003 2004 2005

Control Britton’s beargrass 4 4 4 4 4 Coastalplain honeycombhead 4 8 4 0 0 Coastalplain nailwort 0 4 4 0 0 Earleaf greenbrier 38 71 67 63 63 Eastern milkpea 46 63 50 46 54 Feay’s palafox 0 4 4 17 17 Florida Alicia 29 33 33 33 33 Florida sensitive brier 4 4 4 4 4 Gayfeather 42 50 33 25 38 Lewton’s milkwort 0 4 4 4 4 Milkweed 0 0 4 0 0 Palmetto seedling 96 100 96 92 96 Pineland scalypink 29 25 21 21 13 Queensdelight 0 4 4 4 8 Sandspur 13 0 0 0 0 Saw palmetto 0 4 4 4 4 Scrub buckwheat 4 4 4 8 4 Scurf hoarypea 29 21 33 25 17 Showy dawnflower 0 21 17 17 21 Skyblue lupine 4 8 8 8 4 Trailing milkvine 8 4 0 8 4 Tread softly 8 8 8 17 17 Virginia snakeroot 0 4 0 0 0 Whitemouth dayflower 13 8 13 0 13Burn-only Apalachicola toadflax 0 8 15 8 8 Canadian horseweed 0 0 8 0 0 Coastalplain honeycombhead 0 8 8 0 8 Coastalplain nailwort 0 8 8 0 8 Earleaf greenbrier 69 77 54 69 54 Eastern milkpea 31 62 62 54 85 Feay’s palafox 0 8 15 15 38 Feay’s prairieclover 0 0 15 8 8 Florida Alicia 15 54 38 46 46 Florida scrub roseling 0 15 0 0 0 Florida sensitive brier 8 15 0 8 0 Gayfeather 23 31 23 23 23 Lewton’s milkwort 0 8 8 15 8 Palmetto seedling 100 100 92 100 100 Pineland scalypink 0 31 31 23 31 Queensdelight 0 15 0 0 0 Scrub palmetto 0 0 0 0 8 Scurf hoarypea 0 8 8 8 8 Sickleleaf silkgrass 8 0 0 0 0 Skyblue lupine 0 23 8 0 8 Tread softly 31 23 23 23 31 Whitemouth dayflower 8 0 0 0 0


Table 5. Continued.

Treatment Herb species 2001 2002 2003 2004 2005

Saw-and-burn Apalachicola toadflax 0 25 29 25 17 Brownhair snoutbean 0 4 4 0 0 Canadian horseweed 0 4 13 0 0 Coastalplain honeycombhead 0 8 8 21 29 Coastalplain nailwort 0 4 4 4 13 Earleaf greenbrier 46 46 33 25 29 Eastern milkpea 21 33 42 46 58 Feay’s palafox 4 4 8 8 4 Feay’s prairieclover 0 4 0 0 4 Florida Alicia 17 13 4 13 13 Florida sensitive brier 4 0 0 0 0 Gayfeather 38 38 25 21 38 Lewton’s milkwort 0 8 8 8 8 Longleaf spiderwort 0 0 0 0 4 Milkweed 0 0 4 4 8 Narrowleaf purple everlasting 0 4 0 0 0 Palmetto seedling 100 100 100 100 100 Papery whitlow-wort 0 0 0 4 0 Piedmont blacksenna 0 0 0 0 4 Pineland scalypink 33 46 46 50 54 Queensdelight 8 8 21 17 13 Roundleaf bluet 0 0 0 4 0 Sandspur 4 0 0 0 0 Scrub buckwheat 8 4 4 4 4 Scrub palmetto 0 0 0 0 4 Scurf hoarypea 8 21 21 17 25 Showy dawnflower 0 4 4 0 4 Skyblue lupine 8 38 25 8 13 Tread softly 29 25 21 21 25 Tropical Mexican clover 0 8 0 0 0 Whitemouth dayflower 8 4 0 0 8


and-burn plots, included coastalplain honeycombhead (Balduina angustifolia) (8% in burn-only and 29% in saw-and-burn plots vs. a decline of 4% in controls), pineland scalypink (Stipulicida setacea) (31% in burn-only and 21% in saw-and-burn vs. a decline of 16% in controls), scruf hoarypea (Tephrosia chrysophylla) (8% in burn-only, 17% in saw-and-burn, and a decline of 12% in controls), hairsedge (Bulbostylis spp.) (15% in burn-only, 25% in saw-and-burn, and 5% in controls), and flatsedge (Cyperus spp.) (31% increase in burn-only, 34% in saw-and-burn, and 0% in controls).


Transplant survival.—Overall survival of Florida ziziphus transplants remained high over the course of the study, but it differed among management units. As of the January 2007 annual census, 76.4% of the transplants (110/144) were alive. Survival varied among treatments (Fig. 19), ranging from 89.6% in the control plots to 72.9% in the burn-only plots and 66.7% in

Table 6. Species occurrence matrix for graminoids, displaying the percentage of community plots containing each species in the pre-treatment (2001) and 1-, 2-, 3-, and 4-year post-treatment (2002–2005) surveys at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida.

Treatment Graminoid species 2001 2002 2003 2004 2005

Control Blackseed needlegrass 71 71 75 71 63 Bluestem 63 58 71 67 50 Flatsedge 8 4 4 8 8 Hairsedge 8 17 17 4 13 Lopsided indiangrass 0 0 8 4 0 Sandyfield beaksedge 4 17 13 8 13 Threeawn 96 88 88 88 88 Witchgrass 50 46 46 42 58Burn-only Blackseed needlegrass 62 62 46 62 54 Bluestem 31 38 62 62 62 Flatsedge 0 8 23 23 31 Hairsedge 8 38 31 15 23 Lopsided indiangrass 0 8 0 0 8 Sandyfield beaksedge 8 15 0 0 0 Threeawn 85 85 77 85 85 Witchgrass 38 85 77 85 77Saw-and-burn Blackseed needlegrass 83 38 38 38 38 Bluestem 67 29 33 46 54 Flatsedge 4 0 29 29 38 Hairsedge 8 46 46 33 33 Nutrush 0 0 0 0 4 Sandyfield beaksedge 17 38 21 21 8 Threeawn 75 71 67 71 79 Witchgrass 46 83 71 83 83


the saw-and-burn plots. With the Bonferroni correction for multiple tests (n = 3, α = 0.0167), survival did not differ significantly between the control and burn-only plots (χ2 = 4.376, df = 1, P = 0.036) or the burn-only and saw-and-burn plots (χ2 = 0.445, df = 1, P = 0.505), but it was higher for the control than for the saw-and-burn plots (χ2 = 7.375, df = 1, P = 0.007).

Altogether 34 transplants have died in the 5 years since the introduction. Most mortality (58.8%) took place between the December 2002 and December 2003 censuses, when 7 transplants in the burn-only units and 13 in the saw-and-burn units died. All deaths (n = 5) in the control plots occurred after the 2005 annual census. Seven transplants died back and resprouted during the study, and 5 of these were alive in the 2007 census.

Fig. 19. Survival curves for Florida ziziphus transplants in control, burn-only, and saw-and-burn management units at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2002–2007. The December 2002 and 2003 censuses took place 6 months and 12 months post-introduction, respectively. Beginning in 2005, we censused the population in January, the peak month for flowering.


Transplant Growth and Reproduction.—Surviving transplants did not grow over the 5 years post-introduction, and size was little affected by pre-introduction treatment. Based on the December 2002 census, there were no significant differences among transplants in the 3 treatments for either height (F = 0.099, df = 2, P = 0.905) or maximum crown diameter (mcd) (F = 0.187, df = 2, P = 0.830); transplants were, on average, ~21 cm in height and ~19 cm in mcd. Similarly, there were no significant differences in height (F = 0.023, df = 2, P = 0.877) or mcd (F = 0.162, df = 2, P = 0.850) in the 2007 census, with transplants averaging ~23 cm in height and ~15 cm in mcd. Moreover, growth rates for height and mcd did not differ among the 3 treatments (F = 0.099, df = 2, P = 0.906 and F = 0.419, df = 2, P = 0.659, respectively). There were no significant treatment differences in transplant height between 2002 and 2007 (Table 7), but in all treatments transplants were significantly smaller in mcd in 2007 than in 2002 (Table 7, Fig. 20).

All transplants were small vegetative plants (<50 cm in height) at the time of the introduction and none advanced beyond this stage; no plant flowered during this study. With the exception of resprouts, which occasionally have 2 or more stems, all plants were single-stemmed through the study.

Table 7. Mean ± standard deviation (SD) for height and maximum crown diameter of Florida ziziphus transplants in 3 pre-introduction treatments in 2002 and 2007 censuses at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Also shown are results of paired t-tests for changes in height and mcd between 2002 and 2007.

Variable Treatment Census Mean ± SD Statistics

Height Control 2002 20.43 ± 7.68 t = 1.516, df = 41, P = 0.137 2007 22.57 ± 10.17 Burn-only 2002 22.27 ± 9.81 t = 1.163, df = 32, P = 0.253 2007 23.73 ± 8.57 Saw-and-burn 2002 23.07 ± 9.28 t = 0.263, df = 28, P = 0.795 2007 23.59 ± 9.76Maximum crown diameter Control 2002 19.33 ± 6.71 t = -4.155, df = 41, P < 0.001 2007 15.21 ± 5.84 Burn-only 2002 19.55 ± 6.76 t = -3.223, df = 32, P = 0.003 2007 15.61 ± 7.25 Saw-and-burn 2002 19.66 ± 5.91 t = -5.088, df = 28, P < 0.001


Microhabitat Effects on Transplant Survival.—The October 2004 microhabitat survey of Florida ziziphus found that the distribution of vegetation cover classes did not differ significantly among the 3 treatments (χ2 = 4.391, df = 4, P = 0.356, 3 cells with expected counts < 5); however, the proportion of transplant microsites with vegetation cover >50% in the saw-and-burn units was twice as great as in the burn-only units and 6 times higher than in the control. The distribution of the litter cover classes was also skewed, with the control and burn-only units having more than 3 times greater frequency of transplant microsites in the <50% litter class than the saw-and-burn units, although the significance of the difference could not be assessed due to low expected frequencies. The frequency of encroaching shrubs did not differ among transplants in the 3 treatments (χ2 = 1.003, df = 2, P = 0.605).

In the October 2004 census, most surviving transplants occupied microsites with <10% vegetation cover (95/122 or 77.9%), >50% litter cover (77/122 or 63.1%), and with no encroaching vegetation (107/122 or 87.7%) (Fig. 21). Survival was lower for transplants with >50% vegetation cover (60.0%) than for plants with 10–50% cover (95.5%) or <10% cover (84.8%) (Fig. 21). Percent transplant survival did not differ much among the 3 litter categories, ranging from 87.5% in the >50% litter cover category to 78.6% in the <10% category (Fig. 21), but was higher in the absence of encroaching oaks or palmettos (87.0% to 71.4%) (Fig. 21).

Fig. 20. Change in maximum crown diameter (mcd) of Florida ziziphus transplants in control, burn-only, and saw-and-burn management units at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, between 2002 and 2007.


Fig. 21. Percent surviving Florida ziziphus transplants in 3 vegetation cover and litter cover classes and with or without encroaching shrubs at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, October 2004.

Table 8. Success of alternate models in explaining Florida ziziphus transplant survival at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. The table shows AICc for each of the 11 binary logistic regression models, a measure of the support for the model. K = number of parameters in the model; -2log likelihood = test parameter from the logistic regression model; AICc = corrected Akaike Information Criterion; ∆ AICc = relative AICc for each model compared to the best-supported model; and wi = Akaike weight indicating the degree of support for each model (values range from 0 to 1).

-2 logModela k likelihood AICc ∆ AICc wi

Vegetation cover + encroachment 4 112.159 120.4468 0.0000 0.467Vegetation cover + encroachment + vegetation cover * encroachment 6 110.244 122.8571 2.4104 0.139Vegetation cover + litter cover + encroachment 6 110.402 123.0151 2.5684 0.129Vegetation cover 3 116.974 123.1454 2.6987 0.121Encroachment 2 120.216 124.3011 3.8543 0.067Vegetation cover + litter cover 5 115.769 126.2038 5.7570 0.026Litter cover + encroachment 4 118.172 126.4598 6.0130 0.023Litter cover 3 121.760 127.9314 7.4847 0.011Litter cover + encroachment + litter * encroachment 6 115.461 128.0741 7.6274 0.010Vegetation cover + litter + vegetation cover * litter cover 8 113.091 130.1577 9.7109 0.003All main effects + all 2-way interactions 14 104.567 135.8228 15.3760 0.000

aN = 144 for all models.


The combination of vegetation cover and encroaching shrubs had the greatest support in the AICc evaluation of 11 binary logistic regression models (wi = 0.467) (Table 8), although there was also support for 3 other models. Based on model averaging, the strongest variable in all supported models was vegetation cover. Transplant survival was higher by 25–35% in microsites with lower vegetation cover and higher by 16% in microsites without encroaching shrubs.

Seed Germination and Seedling Survival.—Overall, 3.6% of the 1,728 introduced seeds germinated. The earliest seedlings were recorded ~1 month post-introduction and the latest ~5 months later; peak germination occurred between late August and late September 2002, when we first recorded 61.3% of the 62 seedlings. There was no significant difference in the number of seedlings among the 3 treatments (χ2 = 1.037, df = 2, P = 0.595). Seedling mortality was high for all treatments and, by 2007, only 3 remained.


Our study of scrub buckwheat demography at Carter Creek included 343 plants (through June 2006) growing in 45 3-m-radius circular quadrats. Most plants were tagged pre-treatment, although we continued to locate new plants each year, suggesting that seedling recruitment was ongoing. However, we found no new seedlings after 2004.

Seedlings.—In years with observed seedling recruitment, management treatments had evident (although statistically not analyzable) effects on the appearance of seedlings within the sampling quadrats. Nearly all seedlings were found in the saw-and-burn quadrats. We found no seedlings in the control quadrats, 1 in the burn-only quadrats, and 19 in 7 (of 15) saw-and-burn quadrats. We found seedlings both in patches that were clearly burned and in areas where we could not confidently assign burn status. We found 10 seedlings in 2002 (7 in burned patches, 3 uncertain), 8 in 2003 (5 in burned patches, 3 uncertain), and 2 in 2004 (uncertain).

Plant Survival and Dormancy.—Scrub buckwheat annual survival was consistently high, ranging from 90% to 94% throughout the study. Although in some years survival varied among treatments, cumulative survival through 2006 was not significantly (χ2 = 2.4, df = 2, P = 0.295) affected by treatment: control areas (77.6%), burn-only areas (70.4%), and saw-and-burn areas (79.4%). Higher 2005-06 mortality in the control (8 of 98 plants previously alive) as compared to burn-only (3 of 80) and saw-and-burn (4 of 98) helped eliminate the previous differences seen through 2005. Overall survival (2001–2006) was also similar (χ2 = 1.5, df = 1, P = 0.226) for plants in unburned vs.


burned patches (78.8% vs.72.7%). Taken together, survival over the course of the study was little affected by treatment or by burn status.

Plant dormancy is an occasional feature of scrub buckwheat’s life history. Dormancy (at any time during the study) varied among treatments (χ2 = 7.13, df = 2, P = 0.028), being lower in the saw-and-burn (2.1%) than in the control (8.9%) or burn-only (12.1%) treatments. Dormancy was non-significantly (χ2 = 1.8, df = 1, P = 0.175) higher in unburned (10.0%) than in burned (5.8%) plants. If fire suppression represents a stress to scrub buckwheat, then this higher level of dormancy could represent a stress-induced dormancy, as found in other species. Of the 18 plants dormant for at least 1 post-treatment year between 2002 and 2005, 17 were dormant for only 1 year, while only 1 was dormant for 2 years. All plants had only 1 episode of dormancy during this time.

New non-seedling scrub buckwheat plants appearing during the study may have been plants coming out of dormancy. We noted this appearance mainly in the 2 burned treatments (10 in burn-only, 6 in saw-and-burn, 4 in the control) in the December 2001 postburn survey (13 of 21). Of all plants emerging from dormancy, 60% were in burned patches, 35% in unburned patches, with the burn status of 1 plant (5%) uncertain.

Growth.—Total basal diameter is an effective size measure for scrub buckwheat. The minimum plant size for flowering was total basal diameter of 8 cm (Satterthwaite et al. 2002). Growth was relatively robust in most years of the study (Table 9), with most plants growing from year to year (Table 9). Total growth from the pre-treatment to the 5-year post-treatment census was, on average, positive, and was positive for 60% of individual plants (Table 9).

Table 9. Statistics on annual and cumulative growth of individual scrub buckwheat plants at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2005. Growth is calculated as the difference in total basal diameter (cm).

Time Median Mean Standard % with 25th to 75th period n growth growth deviation growth > 0 percentiles

2001-02 268 +0.2 +0.2 5.87 51 -3.1 to +3.62002-03 272 -0.4 -0.9 5.86 46 -3.6 to +3.12003-04 268 +1.1 +1.2 5.34 57 -1.5 to +4.22004-05 268 +1.1 +1.2 4.43 55 -1.9 to +3.02001-05 258 +0.7 +0.5 5.34 60 -2.5 to +4.9


Although scrub buckwheat growth was initially enhanced by burning, treatment or individual plant burn status (burned vs. unburned) did not generally affect growth. Neither the saw-and-burn nor the burn-only treatments had any effect on 2005–2006 growth (F = 0.56, df = 2, P = 0.570) or on cumulative 2001–2006 growth (F = 2.80, df = 2, P = 0.063). However, growth in the first post-treatment census was greatest for plants in the saw-and-burn treatment (F = 12.5, df = 2, P < 0.001). Plants in the saw-and-burn treatment had significantly higher initial growth than plants in the other 2 treatments (Tukey’s HSD test, P < 0.05). Compared to unburned plants, burned plants had greater growth through the first year postburn (2001–2002; t = 2.6, df = 1, P = 0.009). However, subsequent growth and cumulative 2001–2006 growth (t = 0.52, df = 205, P = 0.605) were not affected by whether plants had burned.

Flowering.—Burning (especially the saw-and-burn treatment) significantly promoted flowering in each of the 4 years postburn, with significant differences based either on treatment or on the burn status of plants. Before treatments, there were no differences in flowering. In each of the 4 years following treatments, flowering percentages were higher in the saw-and-burn than in the burn-only treatment (Fig. 22). In the fifth post-treatment year,

Fig. 22. Proportion of scrub buckwheat plants flowering by date and management treatment (burn-only and saw-and-burn) at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001 (pre-treatment)–2006 (5 years post-treatment).


flowering percentages were not significantly different among treatments (χ2 = 0.97, df = 2, P = 0.615). The attenuation of flowering with time-since-fire (Fig. 22) is probably the cause of the lessening of flowering differences among treatments.

Likewise, burned plants (vs. unburned) had greater flowering for 4 years postfire. There was no difference in the 5-year postburn census flowering in relation to whether an individual plant was burned in 2001 (χ2 = 0.003, df = 1, P = 0.958).

Treatments affected the number of times plants flowered during the study (Fig. 23). Overall, 46% of plants flowered at least once. Most plants that flowered did so in 1 or 2 years, but 2 plants flowered in all 5 post-treatment years. Considering flowering in 0, 1, 2, or 3+ years, treatments had very strong and significant effects on flowering frequency (χ2 = 85.6, df = 6, P < 0.001). Of plants in unburned areas, only 13% flowered; few plants flowered more than once. Of plants in burned areas, 57% flowered, with a single year of flowering most common, and 8% flowering in 3 or more years. Most (65%) plants in the saw-and-burn treatment flowered, most often twice, with 21% flowering 3 or more times in 5 years. With the control plants excluded, the

Fig. 23. Percent of scrub buckwheat plants not flowering or flowering 1, 2, or 3 (or more) times post-treatment at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2002–2006.


saw-and-burn treatment produced more frequent flowering than the burn-only treatment (χ2 = 14.0, df = 3, P = 0.003).

Flowering also occurred more often in plants that were burned (75%) vs. unburned (23%) regardless of treatment (χ2 = 77.2, df = 3, P < 0.001). The most common flowering frequency for burned plants was twice in 5 years (29%), with 20% flowering 3 or more times during the study.

The median number of scrub buckwheat involucres, each of which subtends a small group of flowers, was the best measure of per-plant reproductive output available. The number of involucres in each year (natural log-transformed to achieve normality) was not affected by treatment in 4 of the 5 post-treatment years (e.g., in 2005, F = 0.162, df = 2, P = 0.851). The only year (2002) that differed showed higher involucre numbers in saw-and-burn than in burn-only (t = 2.57, df = 50, P = 0.013); only 1 control plant flowered. Involucre numbers per plant were never affected by whether the plant was actually burned (t-tests, P > 0.12 for each year 2002–2006).

Herbivory.—We commonly observed herbivory, most apparently caused by insects, on scrub buckwheat plants. Annual herbivory values ranged from about 10–50% of plants. In each year, herbivory (vs. no herbivory) did not generally vary among treatments (e.g., for 2006, χ2 = 4.6, df = 2, P = 0.100) or between burned vs. unburned plants (e.g., for 2005, χ2 = 3.70, df = 1, P = 0.063). Herbivory also had no effects on overall (2001–2006) growth (t-tests, P > 0.05 in each case). Over the 5 post-treatment years, most (75%) plants suffered observable herbivory at least once. Most commonly (34% of all plants), we noted a single year with herbivory. No plants had herbivory in all 5 years. The number of years with herbivory (0, 1, 2, 3, or more) did not vary among management treatments (χ2 = 10.2, df = 6, P = 0.116) nor by plant burn status (χ2 =1.9, df = 3, P = 0.588).


Burn Severity and Postburn Recovery.—Seventy-eight percent (384/492) of scrub plum plants in the 2 burn treatments were burned, but severity differed significantly between the burn-only and saw-and-burn treatments (χ2

= 18.103, df = 3, P < 0.001, n = 2, Bonferroni-corrected α = 0.025) (Fig. 24). The percentage of unburned plants in the 2 treatments was not significantly different (χ2 = 1.456, df = 1, P = 0.228). However, the burn-only treatment had a higher percentage of lightly scorched plants than the saw-and-burn treatment (59.0% vs. 48.6%), while the saw-and-burn treatment had a higher percentage of heavily scorched plants (23.7% vs. 15.1%), and the percentage of consumed plants was 4.6 times greater in the saw-and-burn treatment (7.9% vs. 1.7%).


Overall, 99.2% of scrub plum plants in the 2 burn treatments were alive in the first postburn census (February 2002, 6 months postburn). The only 4 dead plants recorded were small individuals with all aboveground parts consumed in the burn.

Postburn Demographic Trends 2002–2007.—As of the 2007 census, cumulative scrub plum survival was 97.6% across the 2 burn treatments. Survival among the 4 burn severity categories varied from 79.2% in the consumed category (19/24) to 100% in the unburned (108/108); in the lightly scorched and heavily scorched categories survival was 97.7% (258/264) and 98.9% (94/95), respectively. Eighty percent of the mortality in the consumed category was due to plants that failed to resprout following the burn, while dead plants in the lightly and heavily scorched categories died 2 or more years after the burn (Fig. 25). Thus, although fire intensity increased postburn mortality, mortality due to fire was lower than mortality due to other causes.

Fig. 24. Percentage of scrub plum plants in 4 burn severity categories for burn-only and saw-and-burn treatments at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001.


Changes in plant height differed significantly over time among the 4 burn severity categories (Pillai’s Trace: F = 12.868, df = 6, 464, P < 0.001) (Fig. 26), and there was a significant interaction between census and burn severity category (F = 2.905, df = 18, 1,398, P < 0.001), indicating that changes over years were effected by burn severity. Across all 7 censuses, plant height differed significantly among the 4 burn severity categories (F = 18.644, df = 3, P < 0.001), with consumed plants significantly shorter than plants in the other 3 categories (P < 0.001 for all pairwise comparisons).

Changes in scrub plum maximum crown diameter (mcd) also differed significantly over time among the 4 burn severity categories (Pillai’s Trace: F = 16.332, df = 6, 464, P < 0.001), with a pattern of decline and recovery similar to the pattern for height. There was a significant census * burn severity category interaction (F = 4.710, df = 18, 1,398, P < 0.001). Across all censuses, mcd differed significantly among the 4 burn severity categories (F = 11.191, df = 3, P < 0.001): unburned plants had significantly greater mcd than plants in the other 3 categories (P ≤ 0.020 in pairwise comparisons), while consumed plants had significantly smaller mcd (P ≤ 0.001).

Fig. 25. Percent survival of scrub plum plants at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 4 burn severity categories over 7 annual censuses, 2001 (pre-treatment)–2007 (6 years postburn).


Scrub plum stem number differed significantly over the 7 years (Pillai’s Trace: F = 83.338, df = 6, 465, P < 0.001), initially increasing dramatically for lightly and heavily scorched plants (Fig. 27). There was a significant interaction between census and burn severity category (F = 11.257, df = 18, 1,401, P < 0.001), indicating that the differences over time were affected by burn severity. Across all censuses, stem number differed significantly among the burn severity categories (F = 9.359, df = 13, P < 0.001). The unburned and consumed categories did not differ from one another, but both differed significantly from the lightly and heavily scorched categories (P ≤ 0.014 in all pairwise comparisons); the lightly and heavily scorched did not differ from each other. Variation in stem number within the 3 burned categories was

Fig. 26. Mean height (±95% confidence interval) for scrub plum plants at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 4 burn severity categories over 7 annual censuses, 2001 (pre-treatment)–2007 (6 years postburn).


greatest in the first 3 postburn years. For example, the lightly scorched and heavily scorched categories showed a 2.6- to 3.2-fold increase in mean stem number in the first postburn census, followed by a slow decline. Both the unburned and the consumed categories showed a slight increase in the first postburn year, followed by minor fluctuations over the next 5 years.

The percentage of scrub plum flowering plants differed significantly among the 4 burn severity categories preburn and in all but the fifth and sixth postburn years (Table 10, Fig. 28). Preburn differences reflected the low frequency of flowering individuals within the consumed category, commensurate with the smaller preburn size of those plants. First year postburn differences reflected

Fig. 27. Back-transformed mean stem number (±95% confidence interval) for scrub plum plants at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 4 burn severity categories over 7 annual censuses, 2001 (pre-treatment)–2007 (6 years postburn).


Table 10. Results of chi-square tests on frequency of flowering scrub plum plants in each of 4 burn severity categories preburn and in 6 postburn censuses at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.

Year χ2 statistic df P-value

Preburn (2001) 16.186 3 0.001 1-year postburn (2002) 86.897 3 < 0.001a

2-year postburn (2003) 21.283 3 < 0.001 3-year postburn (2004) 17.312 3 0.001 4-year postburn (2005) 8.379 3 0.039 5-year postburn (2006) 1.563 3 0.668a

6-year postburn (2007) 5.796 3 0.122a

a1 cell (12.5%) had expected frequency < 5.

Fig. 28. Percentage of scrub plum plants flowering at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, in 4 burn severity categories over 7 annual censuses, 2001 (pre-treatment)–2007 (6 years postburn).


the virtual absence of flowering in the 3 burned categories. Second and third year postburn differences were due primarily to much higher percent flowering for the heavily scorched plants relative to the other categories, suggesting that moderate fire intensity may stimulate flowering. However, there have been no significant differences among categories over the last 2 censuses. Thus, fire-stimulated flowering may be a short-lived phenomenon.

Reproductive output was not much affected by fire severity. The percentage of plants in 3 log10 flowering classes (1–9 flowers, 10–99 flowers, and ≥100 flowers) did not differ significantly among plants in the unburned, lightly scorched, and heavily scorched categories in the 2- to 6-year postburn censuses (Table 11). In most years, 50–60% of plants, irrespective of burn severity category, produced <100 flowers. However, in the 2- and 3-year postburn censuses, there was a trend towards higher flower production in the scorched vs. the unburned categories.

We recorded only 2 seedlings within a 1-m radius of tagged plants.

Table 11. Results of chi-square tests on proportion of scrub plum plants in log10 flowering classes in 5 postburn censuses at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2002–2006.

Year χ2 statistic df P-value

2-year postburn (2002) 2.846 4 0.584 3-year postburn (2003) 5.448 4 0.244a

4-year postburn (2004) 8.629 4 0.071b

5-year postburn (2005) 1.856 4 0.762c

6-year postburn (2006) 5.164 4 0.271d

a1 cell (11.1%) had expected frequency < 5. b2 cells (22.2%) had expected frequencies < 5. c4 cells (44.4%) had expected frequencies < 5. d3 cells (33.3%) had expected frequencies < 5.


DISCUSSION

Sandhill Restoration

Some goals of a successful sandhill restoration are to retain longleaf pines and allow for longleaf recruitment, reduce the hardwood subcanopy, decrease shrub cover, increase graminoid and herb cover, and provide habitat (including bare sand) for rare sandhill endemics (Van Lear et al. 2005). Our research suggests that one-time treatment applications will not be successful in restoring all these key components of high-quality sandhill.

Several components were successfully altered by our treatments. The burn-only and saw-and-burn treatments were successful in reducing the subcanopy and increasing bare sand cover. The saw-and-burn treatment resulted in more bare sand and lower graminoid cover than the burn-only treatment. The saw-and-burn treatment increased some vital rates of sandhill plants. Species composition was stable in response to treatments. Key components of the ground layer (herbs and graminoids) increased only slightly in some cases.

On the other hand, the treatments did not always produce desired changes. The saw-and-burn treatment had the unintended negative effect of increasing longleaf pine mortality. No treatments produced reductions in the shrub layer; in fact, shrub densities rebounded strongly with both burn treatments. Shrub densities can not be reduced by single treatments because shrubs are merely top-killed and quickly resprout. The slight increase in graminoid densities will not be enough to substantially facilitate better movement of low intensity fires along the ground. Increases in herb importance seemed largely driven by increases in the frequencies of weedy native species.

Not unexpectedly, the one-time treatment effects did not permanently alter the sandhill ecosystem. By 4 years post-treatment, the 2 burn treatments were structurally similar to the pre-treatment condition represented by the control. In the initial stages of sandhill restoration, repeated burns may be necessary to control shrubs and increase cover of graminoids and herbs. Frequent burns are critical in restoring and maintaining sandhill ecosystems, perhaps on the order of once every 2–5 years in Ridge sandhill.

Our results indicate that most species were retained following the burn-only and saw-and-burn treatments. Only 2 fire-sensitive species groups, terrestrial lichens and epiphytic bromeliads, suffered significant postburn reductions. Many graminoids (e.g., wiregrass, bluestems [Andropogon spp.], flatsedges, and needlegrass [Piptochaetium avenacoides]) and herbs (e.g.,


coastal honeycombhead, scrub buckwheat, Britton’s beargrass, and scruf hoarypea) resprouted following both burn treatments. Herbs killed by fire (e.g., Apalachicola toadflax, coastalplain nailwort, and pineland scalypink) often increased in abundance postburn due to recruitment from persistent seedbanks (see also Menges and Weekley 2002). These species may have benefited from the increase in bare sand and reduction in ground lichen cover following the burn-only and saw-and-burn treatments.

The saw-and-burn treatment, while having the benefit of increasing fire coverage in our study area, had the negative consequence of increasing longleaf pine mortality. Mortality was higher with the saw-and-burn treatment and was concentrated in areas close to the fuel enhancement zones. Decades of fire suppression have so altered the structure of longleaf pine-wiregrass sandhills that the reintroduction of fire is problematic (USFWS 1999). Mechanical pre-treatments, such as the felling of the oak subcanopy to enhance fire propagation in the absence of graminoid fine fuels, may result in elevated fire intensities lethal even to large and healthy longleaf pines.

If the saw-and-burn treatment was to be applied widely over a large area, pine mortality could be substantially higher than reported here. Our saw-and-burn treatments were applied only within a 15-m radius of the community plots, while pine mortality was measured throughout the saw-and-burn management units. By area, 18% of the saw-and-burn units were chainsawed (range 15–22%). Whether getting fire through a stand is worth this increase in pine mortality will depend on the restoration goals and the density of pines on the site. Because the saw-and-burn treatment may mainly be used to “jump-start” sandhill restoration, elevated pine mortality may be tolerable. Alternatively, techniques to minimize pine mortality (pre-burning around pine trees, using water to minimize residence time, removing fuel from the bases of trees) could alleviate this problem.


Florida ziziphus transplant survival was affected by the pre-introduction sandhill restoration treatments imposed on the Carter Creek site, although not in the ways anticipated at the outset. Surprisingly, transplant survival was higher in the control units than in either the burn-only or the saw-and-burn units. Based on observations of robust Florida ziziphus populations occurring in shade-free pasture sites, we anticipated that reduction (by the burn-only treatment) or removal (by the saw-and-burn treatment) of the oak subcanopy would favor higher rates of transplant survival than the control treatment, which left the subcanopy intact.


However, most Florida ziziphus mortality at Carter Creek occurred ~2 years after the burn-only and saw-and-burn treatments. By 2 years post-introduction (3 years post-treatment), when ~60% of Florida ziziphus transplant mortality occurred, microhabitat conditions around transplants reflected the rapid postburn recovery of co-occurring shrubs. It is possible that lower transplant survival in the treated units reflects competition from re-establishing oak clones and other recovering shrubs. Thus, the 1-year gap between the restoration treatments and the introduction may have nullified the potentially beneficial effects of the treatments for the survival of introduced transplants. On the other hand, it is noteworthy that in the 2005 experimental introduction at The Nature Conservancy’s Tiger Creek Preserve, 1-year post-introduction transplant survival was greater in less open than in more open sites (Weekley et al. 2007a). Recent discoveries of Florida ziziphus in sites ranging from very open to densely vegetated also suggest that it may be able to tolerate a range of vegetation structure.

Over 90% of the transplants used in the Carter Creek introduction originated as seedlings propagated at Historic Bok Sanctuary between 1999 and 2001. Thus, most transplants were between 1 and 3 years of age at the time of the introduction. Although we know from data collected from the in situ populations and from the Bok ex situ population that resprouts and vegetatively propagated plants grow quickly and may flower within 3–5 years, no data are available on seedling growth rates or on how long it takes a seedling to reach sexual maturity. Given the available evidence that Florida ziziphus historically occupied sandhill sites subject to frequent (every 2–5 years) fire, young plants may have routinely burned and resprouted prior to flowering.

Nevertheless, the lack of growth among introduced transplants is worrisome and raises the possibility that nursery-propagated seedlings transplanted to natural sites may not be capable of developing into viable, sexually reproducing populations. Poor growth may reflect these plants being root-bound at the time of transplanting, since transplants had been in pots for as long as 3 years. It is also possible that transplant growth is taking place below ground and that young plants invest more heavily in roots than in stems and leaves as a strategy for dealing with the likelihood of being top-killed within the first few years of life. Fire may stimulate rapid resprouting and flowering in these individuals.

Florida ziziphus transplant survival was >65% even in the saw-and-burn treatment. On the other hand, seed germination was <5%, much lower than the 15–20% germination that we often obtain in lab or greenhouse conditions, and seedling survival was <10%. Five years post-introduction, we recorded 3 live seedlings from the 1,728 introduced seeds (<0.002% establishment rate).


Thus, transplants were more successful than seeds for the establishment of a new population. We obtained similar results from the 2005 experimental introduction at Tiger Creek, where 79% of transplants survived to the 2007 census, but only 1.9% of introduced seeds were represented by live plants (Weekley et al. 2007a).

The Florida ziziphus introduction was designed as an experiment to evaluate the effects of 2 sandhill restoration treatments—burning with and without prior felling of the oak subcanopy—on the survival and growth of transplants, germination of introduced seeds, and survival and growth of seedlings. The Carter Creek project was the first experimental introduction of Florida ziziphus. Although the results were not necessarily what we anticipated, they will inform the design of future experimental introductions.


Both the current research and our previous work (Satterthwaite et al. 2002) indicate that scrub buckwheat populations are well adapted to fire. High long-term (2001–2006) survival was similar in the control, burn-only, and saw-and-burn treatments. Although overall survival of active plants appeared stable among treatments, fires may encourage dormant plants to re-activate. This difference is not likely to have strong effects on demographic responses of scrub buckwheat populations to fire because dormancy (for the Carter Creek plants) appeared rarely and nearly always lasted for only 1 year. This is consistent with patterns seen in a longer-term study of scrub buckwheat at Archbold Biological Station.

As well as survival, several other scrub buckwheat vital rates were unaffected by management treatments. Long-term plant growth rates were unaffected by fire, although growth was initially higher in the saw-and-burn treatment. Herbivory, while common, was unaffected by treatment and did not appear to have serious effects on demographic performance.

Our study is consistent with earlier research (McConnell and Menges 2002) in showing that fire promotes flowering in scrub buckwheat. The proportions of plants flowering were highest within a year of fire and remained higher in burned than in unburned areas for 1–4 years after fire (McConnell and Menges 2002, this study). The saw-and-burn treatment created a higher proportion of flowering plants, partly because of more complete spatial coverage of fire in areas with a chainsawing pre-treatment. Plants in the saw-and-burn treatment flowered more often than plants in the burn-only treatment. Although management treatments affected the proportion of plants flowering, they did not appear to affect the level of reproductive output per plant.


In both burn treatments, flowering percentages attenuated with time-since-fire. The general pattern of decreasing flowering postfire is broadly similar to past patterns with fire in scrub buckwheat (McConnell and Menges 2002). However, in this study, enhanced flowering in the burned treatment continued through 2005 (4 years postfire), while previous research (McConnell and Menges 2002) suggested that enhanced postfire flowering often lasted for shorter periods of time.

Fire appears to favor occasional scrub buckwheat seedling recruitment. Although we recorded few seedlings in this study, nearly all were located in the saw-and-burn treatment. In general, scrub buckwheat seedling recruitment is also highest after fire (Satterthwaite et al. 2002). Litter removal encourages seedling survival and growth (McConnell and Menges 2002), while germination appears high under a variety of conditions (Satterthwaite et al. 2002). Higher seedling recruitment after fires may be due to a combination of seed supply and environmental conditions (e.g., litter removal). The postfire burst of flowering provides germinable seeds to a favorable seedbed in the years after fire. A previous population viability analysis (PVA) established that scrub buckwheat populations should be burned at 5- to 20-year intervals (Satterthwaite et al. 2002).

Given the advantages of fire, mechanical pre-treatments to facilitate the application of fire may be important to scrub buckwheat and other species. In this experiment, the saw-and-burn treatment created a hotter (Wally et al. 2006), more complete fire and more open post-treatment canopies. This had generally favorable effects on scrub buckwheat. The saw-and-burn treatment enhanced seedling recruitment, release from plant dormancy, initial plant growth, and flowering. The flowering effect lasted 4 years post-treatment. Survival, a key vital rate for scrub buckwheat population persistence (Satterthwaite et al. 2002), was not reduced by fire. Therefore, it appears that the saw-and-burn treatment is favorable for the threatened scrub buckwheat.

While the saw-and-burn treatments resulted in complete burns, the burn-only treatment at Carter Creek was incomplete. Therefore, we have also considered whether an individual plant being burned affected demographic responses. Burned plants had higher initial growth and flowered more times over the course of the study than unburned plants. Most seedling recruitment was found in burned areas. The advantages of the saw-and-burn treatment over the burn-only treatment lies, in part, with better fire coverage, so that more individual plants are burned. In addition, the increased fire intensity in the saw-and-burn area did not have negative effects on scrub buckwheat plants growing there. For scrub buckwheat, the saw-and-burn treatment is favorable.



The research presented here further supports our characterization of scrub plum as a strong postburn resprouter (Weekley and Menges 2003a). Resprouting rates recorded at Carter Creek were 100% except for plants in the most severely burned category (83%). Plants consumed by fire were significantly smaller (both before and after burning) than plants in the other 2 burn categories, suggesting that the smallest individuals are most vulnerable to the higher fire intensities associated with the saw-and-burn treatment (Wally et al. 2006).

The most obvious manifestation of scrub plum’s response to fire is the dramatic postburn increase in stem number. As time-since-fire increased, stem number declined as postburn plants rapidly recovered aboveground biomass through growth in height and maximum crown diameter. Fire also stimulates flowering, particularly as measured by the percentage of flowering individuals.

Our data also support previous estimates of low mortality in unburned scrub plum populations (Weekley and Menges 2001). Based on all tagged plants censused over the last 7 years, overall survival was 98%. Of the 20 plants confirmed dead, 5 failed to resprout following fire and 1 apparently died from fallen hurricane debris. The remaining 14 deaths were due to unknown causes. In a restored sandhill maintained by frequent (every 2–5 years) fire, the oak subcanopy would be minimal and the likelihood of shrub mortality or damage due to hurricane debris would be much reduced.

While mortality was low, and scrub plum was resilient to catastrophic events other than fire, our results also support earlier reports that seedling recruitment is negligible (USFWS 1999). To determine the causes of low seedling recruitment, we are investigating the reproductive biology and seed ecology of scrub plum, including a large-scale field germination experiment being conducted at Carter Creek.


MANAGEMENT IMPLICATIONS AND RECOMMENDATIONS

1. Fire is important to sandhill restoration and has generally positive or neutral effects on the endemic shrubs and herbs that were studied. The particular effects vary depending on the restoration component considered (Table 12) and on whether one is considering immediate or longer-term responses. Burning had favorable effects in reducing subcanopy density and lichen cover, increasing bare sand, and promoting resprouting of scrub plum and scrub buckwheat. Burning also promoted flowering in scrub buckwheat for several years. Scrub buckwheat seedling recruitment occurred mainly in the burn-only and saw-and-burn areas. For scrub plum, flowering responses were delayed until the second postburn year.

2. Intense fires, created by the saw-and-burn treatment, have some benefits (e.g., in increasing flowering and growth in scrub buckwheat, propagating fire over larger areas, removing more of the subcanopy than fire can do alone). The intense fires also

Table 12. Summary of the effects of 2 management treatments (in comparison to control) on key components of sandhill restoration, based on data collected at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida, 2001–2007.

Restoration component tested Burn-onlya Saw-and-burn Comments

Reduction of subcanopy + ++ Reduction persisted for 4 yearsReduction of shrub density 0 0 Decreased, then increasedHerb density 0 0 Nonsignificant increases for 4

yearsGraminoid cover 0 0 Temporarily decreasedBare sand + ++ Key microsite for herbsDecreased lichen cover + + Persistent for 4 yearsSurvival of longleaf pines - -- Undesirable effectZiziphus transplant survival - -- Prefers minimal resprouting

coverScrub plum survival 0 - >98% overallScrub plum growth 0 0 High intensity: decreased, then

rapidly recovered preburn sizeScrub plum flowering + + Low first year, then higherScrub buckwheat seedlings + ++ Few seedlings overallScrub buckwheat survival 0 0 Control had marginally higher

survivalScrub buckwheat growth 0 0 Temporary positive effectsScrub buckwheat reproduction + ++ Differences persist for 4 yearsScrub buckwheat herbivory 0 0 Most herbivory minor

a+ = positive effect, ++ = additional positive effect compared to other treatment, - = negative effect, -- = additional negative effect compared to other treatment, 0 = no significant effects or conflicting effects.


created similar benefits to less intense fires on the shrub and herb strata. However, intense fires can have negative effects on longleaf pine survival and the establishment of new populations of Florida ziziphus. Fire temperatures in the saw-and-burn treatment were significantly higher and residence times were longer (Wally et al. 2006) than in the burn-only treatment. Fire managers should take steps to control the fire intensities in initial restoration burns. These steps could include limiting the spatial extent of felled canopy areas, reducing residence time, or reducing fuels (e.g., by raking duff) around longleaf pines.

3. Repeated fires at 2- to 5-year intervals are recommended as sandhill restoration is continued. Subsequent fires should be of lower intensity to avoid some of the problems seen in intense fires. Although we have no data on repeated fires’ effects on Florida ziziphus, they could help revive stagnant populations of this species, and will be beneficial for scrub buckwheat, scrub plum, and other endemic plants. Subsequent fires are likely to be patchy, allowing refugia for fire sensitive species and life history stages. The additional fires will also create favorable post-fire conditions for herbaceous plants and strong resprouters, and they will have positive feedbacks in creating fine fuel that will better carry subsequent fires.

4. At Carter Creek, in collaboration with land and fire managers from the USFWS, we continue to make preparations for a second prescribed burn to take place in management units 1–4 and 7–9 (Fig. 1). (This fire was conducted in December 2007.) The targeted area includes 2 burn-only units (4 and 8) from the 2001 burn, 2 saw-and-burn units (3 and 9), and 3 control units (1, 2, and 7). We are not planning any new saw-and-burn treatments.

5. We recommend further work on longleaf pine responses to mechanical treatments and fires. In the 2001 prescribed fire, longleaf pine mortality was greater in the saw-and-burn treatment than in burn-only treatment. To further investigate the effects of burning on longleaf pines, we have increased our sample of longleaf pines at Carter Creek and are planning to survey all marked pines after the next fire to record their status (e.g., unburned, lightly scorched, heavily scorched) and subsequent survival. This work is ongoing as of February 2008.


6. Similarly, we will monitor Florida ziziphus responses to the next burn, which will include approximately half of the introduced Florida ziziphus population. Florida ziziphus is a vigorous postburn resprouter. We will record postburn status of plants within the burned areas and monitor postburn recovery. We will also compare growth rates of burned and unburned Florida ziziphus plants.

7. We recommend that land managers at Carter Creek sandhill and other sandhill sites work toward re-establishing a natural fire regime, as mandated in the USFWS 1999 recovery plan for Lake Wales Ridge sandhill sites. Historically, longleaf pine-wiregrass sandhills on the Lake Wales Ridge may have burned as often as every 2–5 years (Myers 1990, Menges 1999). Restoration of sandhills degraded by decades of fire suppression requires the re-imposition of frequent fire (K. W. Outcalt, U.S. Forest Service, personal communication). In early restoration phases, it may be beneficial to burn at the frequent end of the natural fire return interval, perhaps with several successive fires at 2-year intervals, to deplete carbon reserves of clonal oaks. Prior to the 2001 prescribed burn at Carter Creek, the sandhill had not burned for several decades. The 2001 burn was successful in reducing the oak subcanopy and in promoting populations of endemic herbs. However, these gains will be lost without the continuing application of prescribed fire at intervals no greater than once every 5 years (the USFWS accomplished a burn in the fall of 2007). In its current biological review (USFWS 2006), the USFWS, which manages the Carter Creek site as part of the Lake Wales Ridge National Wildlife Refuge, recognizes that additional burning needs to take place on the site at the earliest opportunity.


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Appendix A. List of species occurring in 5-m-radius community plots at Carter Creek, Lake Wales Ridge National Wildlife Refuge, Highlands County, Florida. Latin binomials and common names follow Wunderlin and Hansen (2003) unless otherwise noted.

Common name Scientific name Family

Adam’s needle Yucca filamentosa AgavaceaeAmerican burnweed Erechtites hieraciifolius AsteraceaeApalachicola toadflax Linaria floridana VeronicaceaeBallmoss Tillandsia recurvata BromeliaceaeBigflower pawpaw Asimina obovata AnnonaceaeBlackseed needlegrass Piptochaetium avenaciodes PoaceaeBluestem Andropogon spp.a PoaceaeBluestem Schizachyrium spp.a PoaceaeBritton’s beargrass Nolina brittoniana AgavaceaeBrownhair snoutbean Rhynchosia cinerea FabaceaeButterflyweed Asclepias tuberose ApocynaceaeCalloose grape Vitis shuttleworthii VitaceaeCanadian horseweed Conyza canadensis AsteraceaeCapillary hairsedge Bulbostylis ciliatifolia CyperaceaeCarter’s pinelandcress Warea carterii BrassicaceaeChalky bluestem Andropogon virginicus var. glaucus PoaceaeChapman’s gayfeather Liatris chapmanii AsteraceaeChapman’s oak Quercus chapmanii FagaceaeCoastalplain hawkweed Hieracium megacephalon AsteraceaeCoastalplain honeycombhead Balduina angustifolia AsteraceaeCoastalplain nailwort Paronychia hernarioides CaryophyllaceaeCommon dandelion Taraxacum officinale AsteraceaeCommon ragweed Ambrosia artimisiifolia AsteraceaeCorkscrew threeawn Aristida gyrans PoaceaeCup lichenb Cladonia leporinab CladoniaceaeCurtiss’ milkweed Asclepias curtisii ApocynaceaeDarrow’s blueberry Vaccinium darowii EricaceaeDogtongue wild buckwheat Eriogonum tomentosum PolygonaceaeEarleaf greenbrier Smilax auriculata SmilacaceaeEastern milkpea Galactia regularis FabaceaeElliott’s bluestem Andropogon gyrans PoaceaeEvan’s reindeer lichenb Cladina evansiib CladoniaceaeFeay’s palafox Palafoxia feayi AsteraceaeFeay’s prairieclover Dalea feayi FabaceaeFlatsedge Cyperus spp.a CyperaceaeFlattop mille graines Hedyotis corymbosa RubiaceaeFlorida Alicia Chapmannia floridana FabaceaeFlorida greeneyes Berlandiera subacaulis AsteraceaeFlorida perforate cladoniab Cladonia prostratab CladoniaceaeFlorida scrub frostweed Helianthemum nashii AsteraceaeFlorida scrub roseling Cuthbertia ornata CommelinaceaeFlorida sensitive brier Mimosa quadrivalvis FabaceaeFlorida ziziphusc Ziziphus celata RhamnaceaeGarberia Garberia heterophylla AsteraceaeGayfeather Liatris spp.a AsteraceaeGopher apple Licania michauxii ChrysobalanaceaeHairy dawnflower Stylisma villosa ConvolvulaceaeHemlock witchgrass Dichanthelium sabulorum PoaceaeHog plum Ximenia americana OlacaceaeLargeflower jointweed Polygonella robusta Polygonaceae


Appendix A. Continued.


Lewton’s milkwort Polygala lewtonii PolygalaceaeLongleaf pine Pinus palustris PinaceaeLongleaf spiderwort Tradescantia roseolens CommelinaceaeLopsided indiangrass Sorghastrum secundum PoaceaeMichaux’s hawthorn Crataegus michauxii RosaceaeMilkweed Asclepias spp.a ApocynaceaeMuscadine Vitis rotundifolia VitaceaeMyrtle oak Quercus myrtifolia FagaceaeNarrowleaf purple everlasting Gnaphalium falcatum AsteraceaeNutrush Scleria spp.a CyperaceaePanicgrass Panicum spp.a PoaceaePapery whitlow-wortd Paronychia chartacea spp. chartacead CaryophyllaceaePartridge pea Chamaecrista fasciculata FabaceaePennsylvania everlasting Gnaphalium pensylvaticum AsteraceaePiedmont blacksenna Seymeria pectinata ScrophulariaceaePigeonwings Clitoria fragrans FabaceaePigmy fringetree Chionanthus pygmaeus OleaceaePineland pinweed Lechea sessilifolia CistaceaePineland scalypink Stipulicida setacea CaryophyllaceaePinewoods milkweed Asclepias humistrata ApocynaceaePitted stripeseed Piriqueta caroliniana TurneraceaePricklypear Opuntia humifusa CactaceaeQueensdelight Stillingia sylvatica EuphorbiaceaeReindeer lichenb Cladina subtenuisb CladoniaceaeRoundleaf bluet Houstonia procumbens RubiaceaeSand live oak Quercus geminata FagaceaeSand pine Pinus clausa PinaceaeSand spike-moss Selaginella arenicola SelaginellaceaeSandspur Krameria lanceolata KrameriaceaeSandyfield beaksedge Rhynchospora megalocarpa CyperaceaeSavannah milkweed Asclepias pedicellata ApocynaceaeSaw palmetto Serenoa repens ArecaceaeScrub buckwheat Eriogonum longifolium var. gnaphalifolium PolygonaceaeScrub hickory Carya floridana JuglandaceaeScrub palmetto Sabal etonia ArecaceaeScrub plum Prunus geniculata RosaceaeScurf hoarypea Tephrosia chrysophylla FabaceaeShiny blueberry Vaccinium myrsinites EricaceaeShortleaf gayfeather Liatris tenuifolia AsteraceaeShowy dawnflower Stylisma abdita ConvolvulaceaeSickleleaf silkgrass Pityopsis graminifolia AsteraceaeSkyblue lupine Lupinus diffusus FabaceaeSlenderleaf clammyweed Polanisia tenuifolia BrassicaceaeSouthern needleleaf Tillandsia setacea BromeliaceaeSpanish moss Tillandsia usneoides BromeliaceaeTexas signalgrass Panicum texanum PoaceaeThreeawn Aristida ssp.a PoaceaeTough bully Sideroxylon tenax SapotaceaeTrailing milkvine Matelea pubiflora AsclepiadaceaeTread softly Cnidoscolus stimulosus EuphorbiaceaeTropical Mexican clover Richardia brasiliensis RubiaceaTurkey oak Quercus laevis Fagaceae


Appendix A. Continued.


Velvetleaf milkweed Asclepias tomentosa ApocynaceaeVirginia snakeroot Aristilochia serpentaria AristolochiaceaeWare’s hairsedge Bulbostylis warei CyperaceaeWavyleaf noseburn Tragia urens EuphorbiaceaeWhitemouth dayflower Commelina erecta Commelinaceae

aClosely related species difficult to distinguish in field. bPlants Database (USDA 2007). cName commonly used by Archbold Biological Station Plant Ecology Lab and co-workers. dU.S. Fish and Wildlife Service (1999); Paronychia chartacea used by Wunderlin and Hansen (2003).

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