Riparian Revegetation Using Native Seed: Feasibility Studies on the Lower Colorado RiverGrabau, Matthew R.1, Milczarek, Michael A.2, Garnett, G.3, Bunting, Daniel P.4, Karpiscak, Martin4, Lewis, Elizabeth4, and David Quanrud4
1GeoSystems Analysis, Inc., Tucson, Arizona, USA, [email protected] Analysis, Inc., Tucson, Arizona, USA
3US Department of the Interior, Bureau of Reclamation, Boulder City, Nevada, USA4The University of Arizona Office of Arid Lands Studies, Tucson, Arizona, USA
Ongoing Efforts:
1. Long-term monitoring of small-scale field study plots to determine irrigation regime effects and long-term vegetation dynamics.
2. Additional small-scale study plots seeded with Goodding’s willow alone to eliminate competition with cottonwood. More intensive weed control is also
being implemented.
Proposed Future Work:
1. Pilot-scale revegetation project on the lower Colorado River to evaluate scaling effects and logistics for large-scale seed collection, storage, and application.
Conclusions:
1. Viability of Fremont cottonwood, Goodding’s willow, and coyote willow seed can be extended to greater than two years by freezing.
2. Soil conditions (bulk density, texture and fertility) and seeding rates can significantly affect plant establishment, growth, and species diversity. In general, sandy or compacted soils reduce plant vigor; higher seeding rates
result in greater plant establishment, although the rate of establishment decreases at higher seeding rates.
3. Direct seeding resulted in dense cottonwood and willow establishment. Best results were observed with hydroseeding of un-cleaned seed onto furrows.
4. Tree establishment rates of approximately 10% were observed in field plots for
Fremont cottonwood seeded at 25 PLS/ft2.
5. Tree establishment rates of approximately 1% were observed in field plots for
Goodding’s willow at 150 PLS/ft2.
6. Saltcedar (Tamarix ramosissima), an introduced species, established at higher density than seeded native species. However, after one growing season
saltcedar was primarily in the cottonwood understory and has experienced higher mortality than Fremont cottonwood.
7. Revegetation by direct seeding appears feasible using standard seed collection,
preservation, application, and irrigation techniques. Additionally, direct seeding can increase genetic diversity and reduce costs compared to vegetative
propagation techniques.
8. Intensive grass and broadleaf weed management is necessary in retired agricultural fields prior to, and after revegetation by direct seeding.
Results
Restoring native riparian plant communities is a major objective of
management agencies in the West, with significant plans to revegetate areas currently farmed or dominated by invasive species with cottonwood and
willow (e.g. USBR 2004). Vegetative propagation and subsequent planting
of potted plants or rooted cuttings is currently the standard method of
revegetation (Raulston 2003). If direct seeding can be achieved, restoration costs might be dramatically reduced while increasing tree density and
maximizing genetic diversity within restoration areas.
Passive revegetation from seed occurs in natural and managed riparian
ecosystems where moist, bare soil is available during seed dispersal as a result of favorable hydrologic conditions. Examples include reintroduction of
periodic flooding (e.g. Nagler et al. 2005) or managed drawdown of ponds
during periods of seed dispersal (e.g. Roelle et al. 2001). Direct seeding of
cottonwood and willow has not yet been implemented in large-scale restoration due to perceived limits of seed viability (Young and Clements
2003) and an unproven record of success (Raulston 2003).
The Bureau of Reclamation is conducting feasibility studies to assess
revegetation of riparian trees along the lower Colorado River using native seed. Feasibility studies conducted to date consist of a three year, phased
germination, greenhouse, and field study program focused on Fremont
cottonwood (Populus fremontii), Goodding’s willow (Salix gooddingii), and
coyote willow (Salix exigua).
Introduction
Methods
DiscussionStudy Locations and Implementation
References
We thank the Bureau of Reclamation LCR office for their continued support and funding of these efforts. In particular thank you to Barbara Raulston for initiating the
project. Thanks to Dr. Stephen P. McLaughlin (The University of Arizona Office of Arid Lands Studies) for his guidance on seed preservation techniques. Thanks to Dr. Leslie Gunatilaka for accommodating research efforts at the University of
Arizona Office of Arid Lands Studies. Thanks to Bill Seese, Mike Oldham and all Cibola NWR staff for their support in implemented field studies. Thanks to Havasu
NWR, Bill Williams NWR, and the Ahakhav Tribal Preserve for permission and guidance for native seed collection. Thanks to Riverbottom Farms for assistance in
field preparation and irrigation. Thanks to all of the University of Arizona student employees for their assistance in all phases of the study. Without all of these
individuals, this project would not have been a success.
Nagler, P. L., O. Hinojosa-Huerta, E. P. Glenn, J. Garcia-Hernandez, R. Romo, C. Curtis, A. R. Huete, and S. G. Nelson. 2005. Regeneration of native trees in the presence of
invasive saltcedar in the Colorado River Delta, Mexico. Conservation Biology 19:1842-1852.
Raulston, B. E. 2003. Habitat restoration on the lower Colorado River, demonstration
projects: 1995-2002. US Department of the Interior, Lower Colorado Regional Office, Boulder City, Nevada. 36 pp.
Roelle, J. E., D. N. Gladwin, and B. S. Cade. 2001. Establishment, growth, and early survival
of woody riparian species at a Colorado gravel pit. Western North America Naturalist 61:182-194.
USBR. 2004. Lower Colorado River Multi-Species Conservation Plan, Volume II: Habitat
Conservation Plan. Final. December 17. (J&S 00450.00.) Sacramento, CA.
Young, J.A., and C.D. Clements. 2003. Germination of Seeds of Fremont Cottonwood. Journal of Range Management 56:660-664.
0%
20%
40%
60%
80%
100%
Apr-06 Jul-06 Oct-06 Feb-07 May-07 Aug-07 Dec-07 Mar-08 Jun-08
Germination Trial Date
Via
bilit
y
Cleaned, Ambient T, w/ O2 Uncleaned, Frozen, w/ O2
Uncleaned, Frozen, No O2 Seed Collection
Storage
Treatment:
~0% viability for all room
temperature storage
after 19 w eeks.
Phase 1: Germination Study
0%
20%
40%
60%
80%
100%
Apr-06 Jul-06 Oct-06 Feb-07 May-07 Aug-07 Dec-07 Mar-08 Jun-08
Germination Trial Date
Via
bility
Cleaned, Ambient T, w/ O2 Uncleaned, Frozen, w/ O2
Uncleaned, Frozen, No O2 Seed Collection
Storage
Treatment:
~0% viability for all room
temperature storage
after 17 w eeks.
Figure 2: Coyote willow seed viability over time.
0%
20%
40%
60%
80%
100%
Apr-06 Jul-06 Oct-06 Feb-07 May-07 Aug-07 Dec-07 Mar-08 Jun-08
Germination Trial Date
Via
bilit
y
Cleaned, Ambient T, w/ O2 Uncleaned, Frozen, w/ O2
Uncleaned, Frozen, No O2 Seed Collection
Storage
Treatment:
~0% viability for all room
temperature storage
after 17 w eeks.
Figure 3: Goodding’s willow seed viability over
time.
Figure 1: Fremont cottonwood seed viability over time.
Phase 1 and Phase 2Seed Collection: Lower Colorado River
Seed Processing, Germination, and Greenhouse Studies:
The University of Arizona Southwest Center for Natural Products Research and Commercialization, Tucson, Arizona
Germination Studies
7-Gallon Pot Studies
Phase 1: Germination study (April 2006-August 2008).
Objective: Determine potential for long-term seed storage.
● Collection of native seed from various locations on the lower Colorado River (LCR)
● Experimental preservation methods: room-temperature storage, freezing, and oxygen removal.
● Periodic viability analysis over time.
● Germination tests in incubators and on soil beds at different temperatures.
Phase 2: Greenhouse study (May 2006-September 2006).
Objectives: 1) Determine establishment rates from direct seeding of Fremont
cottonwood, Goodding’s willow, and coyote willow. 2) Determine if seed cleaning increases establishment rates. 3) Determine the effects of soil
texture, compaction, and organic fertilizer on establishment and growth.
4) Determine the effect of seeding rates on growth and species
composition.
● Loose soil, compacted soil, or sandy soil.
● Cleaned or un-cleaned seed.
● Biosol (organic fertilizer) at 0 kg/ha or 1680 kg/ha.
● Total seeding rates of 129 PLS/m2, 646 PLS/m2, or 3229 PLS/m2, 1/3 each
of Fremont cottonwood, Goodding’s willow, and coyote willow.
Phase 3: Small-scale field study (May 2007-September 2009).
Objectives: 1) Determine establishment rates for direct seeding of riparian
species. 2) Determine the effectiveness of large-scale seeding and
irrigation methods.
● Seeding rate of 1076 PLS/m2 as 40% Goodding’s willow, 40% coyote
willow, and 20% Fremont cottonwood.
● Hydroseeding and broadcast seeding onto furrowed or level plots.
● Sprinkler irrigation for three weeks or surface irrigation only.
● In-situ soil moisture content, temperature, and EC monitoring network: Soil temperature and EC at 15 cm below ground surface (bgs) in each plot.
Soil moisture at 15, 45, and 91 cm bgs. Groundwater elevation monitoring
through a network of ten piezometers.
● Initial and long-term analysis of vegetation success: Establishment,
growth, and survival.
Split-block factorial design:
Phase 2: Greenhouse Study
Without Organic Fertilizer
Loose Soil Compacted Soil Sandy Soil Loose Soil Compacted Soil Sandy Soil
With Organic Fertilizer (BiosolTM)
Results
POFR
Stems/m2
SAGO
Stems/m2
SAEX
Stems/m2
POFR
g/m2
SAGO
g/m2
SAEX
g/m2
Soil Type
Loose 238 A 110 A 93 B 435 A 122 A 13 AB
Compacted 265 A 117 A 175 A 258 B 86 A 20 A
Sand 244 A 95 A 114 B 217 B 9 B 7 B
Seed Type
Cleaned 328 A 137 A 207 A 368 A 74 A 20 A
Un-Cleaned 170 B 78 B 48 B 239 B 71 A 6 B
Biosol Rate
0 kg/ha 284 A 140 A 161 A 268 B 67 A 13 A
1680 kg/ha 214 B 74 B 93 B 339 A 78 A 14 A
Seeding Rate
129 PLS/m2 32 C 16 C 51 B 116 C 41 B 13 A
646 PLS/m2
119 B 82 B 105 B 229 B 78 AB 15 A
3229 PLS/m2
596 A 223 A 226 A 566 A 98 A 12 A
Least-Squared Means
Table 2: Linear ANOVA model results after one growing season for Fremont cottonwood (POFR), Goodding’s willow (SAGO), and
coyote willow (SAEX).
Major Findings:
• Soil type affected tree biomass (loose>compacted>sand).
• Compacted soil decreased root penetration.
• Application of cleaned seed resulted in twice the establishment of un-cleaned seed.
• Organic fertilizer increased growth rates in sand, but did not
increase growth rates in loose or compacted soil.
• Organic fertilizer decreased tree establishment rates.
• Higher seeding rates resulted in higher stem density, but
favored POFR dominance (out-competition of willow species).
• Higher seeding rates resulted in reduced POFR growth rates.
• Higher seeding rates reduced establishment and growth of
volunteer species.
Phase 3: Small-Scale Field Study
0
2
4
6
8
10
12
14
16
Border Furrow Border Furrow Border Furrow
Broadcast Hydroseed Hydroseed
Cleaned Seed Un-Cleaned Seed
Treatment
Dry
Bio
ma
ss, g
ram
s/m
2
POFR
TARA
Grass and Sedge Average Dry Biomass: 106 g/m2
Figure 4: Fremont cottonwood (POFR) and saltcedar (TARA) dry biomass after four months of growth.
July 2007-Two Months of Growth in Furrow
Plot: Cottonwood Establishment Along
High-Water Mark
June 2009-POFR Density and
Height After Two Growing Seasons
Table 3: Linear ANOVA model results after two growing seasons for Fremont cottonwood (POFR), Goodding’s willow (SAGO), and coyote willow (SAEX).
Results
POFR
Stems/ m2
SAGO
Stems/m2
SAEX
Stems/m2
TARA
Stems/m2
POFR
Crown
Cover
TARA
Crown
Cover
POFR
Canopy
Cover
TARA
Canopy
Cover
POFR
Average
Height, cm
TARA
Average
Height, cm
Sprinklers
No Sprinklers 13.9 A 0.288 A 0.113 A 22.4 A 0.74 A 0.11 A 0.76 A 0.47 A 212 A 76 A
Sprinklers 11.8 A 0.082 A 0.072 A 6.39 B 0. 41 B 0.13 A 0.43 B 0.25 B 150 B 75 B
Seed Treatment
Un-cleaned Hydroseed 17.9 A 0.437 A 0.166 A 14.9 A 0.62 A 0.13 A 0.65 A 0.38 A 176 A 80 A
Cleaned Hydroseed 10.4 A 0.004 B 0.105 A 17.0 A 0.57 A 0.12 A 0.59 A 0.38 A 199 A 77 A
Cleaned Broadcast 10.2 A 0.115 B 0.007 A 11.3 A 0.54 A 0.10 A 0.56 A 0.32 A 167 A 69 A
Surface Irrigation Method
Border 10.3 A 0.152 B 0.035 A 16.2 A 0.46 B 0.13 A 0.48 B 0.34 A 154 B 74 A
Furrow 15.3 A 0.218 A 0.150 A 12.6 A 0.69 A 0.10 A 0.72 A 0.38 A 207 A 76 A
Least-Squared Means
Major Findings:
• POFR establishment of 7% of PLS rates.
• SAGO and SAEX establishment of less than 1% of PLS rates.
• Sprinklers did not increase tree establishment and decreased growth rates.
• Hydroseeding eliminates the need for seed
cleaning.
• Furrow irrigation encouraged higher growth
rates and more even tree distribution.
• Higher growth and survival rates for Fremont cottonwood than Goodding’s or coyote willow.
• Volunteer saltcedar establishment was higher than seeded tree establishment.
• Saltcedar growth rates were lower than
cottonwood.
Acknowledgements
Phase 3
Small-Scale Field Studies:
Cibola National Wildlife Refuge, Cibola, Arizona
Site Characterization
Small-Scale Study Implementation
Soil TextureSoil Salinity
Vegetation MonitoringSite Preparation and Seeding
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