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Table 1. Significant Spearman's rank correlations (p)of bee abundance and species richness with habitatvariables following application of a Bonferroni correc-tion (a level 0.05/1 4 = 0.004) for treatm ent units (thinonly, burn only, thin + bu rn, and control) in a pinyon-juniper woodland, Arizona. Nonsignificant findings arenot shown.

Total beesHabitat variable

Bee species

MayFlower cover (per m^^)Number of floweringspeciesAugust

Flower cover (per m^)% cover litter% canopy cover

0.58 < 0.0001 0.54 < 0.0001

0.51 0.0002 0.48 0.0005

0.44 0.0020-0.41 0.0034-0.44 0.0016

variables, was most strongly correlated witb bee abundanceand species richness (Table 1). The bigb flower cover in tbe

tbin plus burn treatments may be attributed to the moreopen canopy found in these units, since canopy cover intbe thin only and thin plus burn treatments was signifi-cantly lower than in the control and burn only plots{p

$ 0.4m

.^ 0.2X

0.0

1

ft 1 I Cassiaazzz2 Tabebuia

ab

1

f l

l

1

anNDControl Edge Interior Plantation

IslandFigure 1. Mean ( SD) percent germination (A), survival (B), and height(C) after one year of Cassia fistuloso an d Tabebuia rosea seeds acrossfour microhabitats: control (abandoned pasture), tree island edge andinterior, and tree plantation (Agua Buena, Costa Rica). Values with thesame letter are not significantly different; ND = no data.

Overall field germination was 20.6% forCassia and17.7% for Tahebuia. Psidium seeds germinated in the shadehouse but not in the field. MoreCassia seeds germinatedat island edges compared to other microhabitats, whereasTabebuia germination did not differ across microhabitats(Figure lA) . .

There was a trend toward higherCassia survival in theisland interior and p lantatio n m icrohab itats after 1 year,but it was not significant given the high variance (FigureIB) . Tabebuia seedling survival was higher at island edgesafter six months, but by the end of the study few seedlingssurvived in any treatment, and none survived in the control(Figure 1B). 'Ihe n um ber of seedlings rema ining after on eyear did not differ by treatment for either species{Cassia:p = 0.474; Tabebuia: p - 0.349). Given low germinationand survival, only a small percentage of seeds resulted insurviving seedlings{Cassia: 3.7% 5 . 1 % ; Tabebuia: 0.88%

1.7%). Cassia seedlings had lower survival in areas of

high grass cover [P- = 0.42, F= 9.3, df = 1,26,; = 0.009),whereas Tabebuia seedling survival was low in most plots.Cassia seedlings were significantly taller in the plantationafter 1 year (Figure lC). Tabebuia seedling height showed asimilar trend b ut it was not significant du e to high variance.

Result uFthis and previous sttidies clearly show that pas-ture grass com petition limits seedling survival and grow th

(Chapman et al. 1999, Holl 2002a). Therefore, restorationefforts in abandoned agricultural land in the tropics shouldaim to reduce grass cover. One of the most effective waysto achieve this goal is to establish a tree canopy that shadesout light-demanding grasses.

Our results are consistent with past research (e.g.,Hooper et al . 2002, Doust et al . 2006) showing that ger-mi nati on of small-seeded species in restored tropical forestsis generally low beneath a range of canopy environments,and this, therefore, is one factor that will slow recovery.Higher Cassia seed germ ination at island edges suggests thatintermediate canopy cover favors seedling establishment in

this species. The intermediate canopy cover of the islandrestoration strategy created broader daily temperaturechanges than in other microhabitats, which may havetriggered germination.

Ot he r factors besides microclim ate, such as high herbiv-ory and seed prdation, may have reduced germ ination andsurvival. Smaller seedlings may also have been smotheredby leaf litter (Vzquez-Yanes and Orozco-Segovia 1993).Seed prdation and poor seed-soil contact (Doust et al.2006) may explain the complete lack of germination inthe field for Psidium, as seeds germina ted in a shade housein trays with soil.

The low seed germinatio n and seedling survival suggestthat small seeds must be dispersed or seeded in large quan-tities for successful establishment in recovering tropicalforests (Holl 2002b, Hooper et al. 2002). Planting treeseedlings, using either the island or plantation strategy,serves to reduce grass cover and enhance survival andgrowth of naturally establishing seedlings. The higherseedling growth in both plantations and island interiorswas likely due to the planting of the two nitrbgen-fixingtree species, which may function as nurse trees (see Holl200 2b). T he island-planting strategy creates m ore heteroge-neous abiotic conditions, which are likely to better mimictropical forests wh ich are quite pa tchy naturally.

AcknowledgmentsWe are grateful for field research help from R. Gomez. M. Loik,J.L. Reid, and J.A. Rosales. Financial support for this project wasprovided by a NSF grant (DE B 05-1 5577 ), the Richard A. CooleyMemorial Endowment, and UCSC College Eight Project Funds.

ReferencesChapm an, C.A., LJ. C hapman , L. Kaufman and A.E. Zanne.

1999. Potential causes of arrested succession in Kibale

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National Park, Uganda: Grow th and mortality of seedlings.African journal ofEcobgy 37:81-92.

Cole, R.J., K.D. Holl and R.A. Zahawi. Forthcoming. Seed rainunder cree islands planted to restore degraded lands in atropical agricultural landscape.Ecological Applications.

Doust, S .j., P.D. Erskine and D . Lamb. 2006 . Direct seedingto restore rainforest species: Microsite effects on the earlyestablishment and growth of rainforest tree seedlings on

degraded land in the wet tropics of Australia.Forest Ecobgyand Management234:333-343.Holl, K.D. 2002a. Eifect of shrubs on tree seedling establishment

in abandoned tropical pasture.Journal ofEcology90:179-187.. 2002b. Tropical moist forest. Pages 539-558in M.R.Perrow and A.J. Davy (eds).Handbook of EcologicalRestoration. Cam bridge UK : Cam bridge University Press.

Hooper, E., R. Condit and P. Legendre. 2002. Responses of 20native tree species to reforestation strategies for abandonedfarmland in Panama.Ecological Applications12:1626-1641.

Vzquez-Yanes, C. and A . Orozco-Segovia. 1993 . Patterns of seedlongevity and germination in the tropical rainforest.AnnualReview ofEcology an d Systematics 24:69-87.

Zahawi, R.A. and C.K. Augspurger. 2006. Tropical forestrestoration: Tree islands as recruitment foci in degraded landsof Honduras. Ecological Applications16:464-478.

Ponderosa Pine Understory Response toShort-Term Grazing Exclusion (Arizona)Christopher D. Sorensen (School of forestry, Northern Ari-zona University, Box 15018, Flagstaff, AZ 86011) andChristopher M. McG lone (Ecological Restoration Institute,Northern Arizona University, Box 15017, Flagstaff, AZ8601L 928/556-9004, chris.mcgbne@nau.edu)

Livestock grazing is a pervasive land use practice onpublic lands in rhe American Southwest, making it animportant variable in land management practices. Whilemost grazing allotments are stocked each year, shorr restperiods (1-2 years) are used ro minimize potential negativeimpacts of grazing and to sustain range resources (Curtin2002). Moore and others (1999) specifically recommenddeferment of livestock grazing on ponderosa pine{Pinus

ponderosa) forests after thinning and burning as ecologicalrestoration treatments. Few data are available, however,on the influence of short-term grazing exclusion on theunderstory plant community of pine forest restorationprojects. In this study, we attempt to quantify the impactsof cattle grazing on p lant cover, species richness, and non -native species on a ponderosa pine restoration project innorthern Arizona.

In die summer of 2005, the Arizona Game and FishDe pa rtm ent erected several 35 m x 35 m cattle exclosures atthe M t. Trum bull, Arizona, ecological restoration researchsite on the Grand Gany on-Parashant National M onu men t.

Ungrazed ' ConlroiUng razed ' TreatedGrazed * ControlGrazed * Treated

Figure 1. Median (25t h, 7Sth percentiies) cheatgrass cover per plot,separated by both grazing and restoration treatments. Results ofKruskal-Wallis ran ked signs analysis were sign ificant fo r year x gr azing xrestoration (treated vs. control) interaction (x' = 32.01, p = 0.00 1 ).

W e used these exclosures to evaluate the sh ort-te rm effectsof cattle exclusion on the herbaceous understory in aponderosa pine forest. We established ten paired plotsconsisting of a grazing treatment exclosure and a similarlysized grazed co ntro l. O f the ten pairs, five were located ina thinned and burned forest and five in unrestored areas.The plots were dispersed across the 1,200 ha Little Springpasture of the Mt. Logan allotmen t, where elevations rangefrom 2,000 to 2,250 m, and the mean annual precipitationfrom 2 002 to 2007 was 413 m m (WR GG 2 007) . Gat t legrazing occurs on the Mt. Logan allotment only from Julythrough October at a maximum stocking rate of 13.6 ha/AUM (Whit Bunt ing, BLM , pers. comm .) . In 20 06. how-ever, grazing p ressure was reduced by a break in a fence th atallowed cattle to stray into the adjacent Tuweap allotment.

The unrestored sites within the project are predomi-nantly dense stands of ponderosa pine with thick litterand duff layers and a sparse understory. The restored ateaswere thinned and burn ed to emulate pre-1870 tree densityand distribution. Restoration treatment areas have a morediverse and abundant understory community and substan-tially fewer trees per hectare (399.2) than the prerestorationconditions (784 .6) and the untreated con trols (873.5). All

restoration treatments on our study plots were completedby 2001 (see Roccaforte et al. 2009 for details), and cattlewere reintroduced in the summ er of 200 2 (W hit Bun ting,BLM, pers. comm.).

The dominant tree species is ponderosa pine, thoughthere is a considerable amo un t of Gam bel oak{Quercusgambelii) on site. The m ain native species are silver lu pine{Lupinus argenteus) and the important perennial foragegrasses bottlebrush squirreltail{Elymus elymoides) and west-ern wheatgrass {Pascopyrum smithii). In 2003 , cheatgrass{Bromus tectorum)invaded the site. Gheatgrass is the mostabundant non-native species present, and this annual grass

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