Direct Seeding for Riparian Habitat Revegetation Feasibility Study Lessons. 23 February, 2010

Transcription

1 Direct Seeding for Riparian Habitat Revegetation Feasibility Study Lessons 23 February,

2 Presentation Overview 1. Why direct seeding? 2. Methods and results for 4-year study on seeding. 3. Suggestions for next steps. 2

3 Perceived Problems with Vegetative Propagation Genetic bottlenecks (Winfield and Hughes, 2002). Lack of habitat design criteria. Tree density, soil moisture, etc. Low diversity and little heterogeneity in restoration areas. High costs. $1.77 per tree = >$10,000/ha (>$4,000/acre). For trees only. Does not include site preparation, project management, or irrigation costs. (Bureau of Reclamation, 2007) 3

4 Potential Benefits of Native Seed Application Preservation of remaining genetic diversity. Potential for very high plant densities: Improved native species habitat? Increased competitive advantage over saltcedar and other undesired species? Economic efficiency. Direct seeding might reduce revegetation costs by over 90% (Schuman et al., 2005). 4

5 Challenges of Native Seed 1. Seed Biology: Periods of viability for Fremont cottonwood, Goodding s willow, and coyote willow unknown. Literature speculates one month maximum (Stromberg, 1993; Young and Clements, 2003). 2. Seed Placement: Fluffy seed very difficult to handle and keep in place (Raulston, 2003). 3. Irrigation challenges. Maintain high soil moisture. Minimize overland flow. 4. Volunteer (weed) species. 5

6 Study Objectives Analyze the feasibility of direct seeding of riparian species for revegetation: 1. Determine effects of seed treatment and storage methods on long-term viability and vigor of riparian tree seed. 2. Determine the effects of: soil conditions; seeding rates; seed cleaning; and seeding methods on tree establishment and growth. 3. Optimize irrigation methods for tree establishment. 4. Determine establishment rates for different seed application methods and rates. 6

7 Study Phases Four phases for the analysis of direct seeding methods for revegetation: 1. Laboratory and greenhouse study of seed storage. 2. Controlled environment (greenhouse) seeding study. 3. Small-scale field study plots at Cibola NWR. 4. Large-scale demonstration plots (proposed). 7

8 Phase 1: Long-term Viability and Vigor Analysis Collect riparian seed from natural and planted trees on the lower Colorado River (April 2006). Evaluate seed storage techniques: Frozen vs. room-temperature storage. Ambient oxygen vs. oxygen removal. Seed cleaning (hair removal) versus no seed cleaning. Monitor germination rates over time (May 2006-July 2008). Greenhouse study of seed vigor after one year of storage in freezers (Summer 2007). 8

9 Conclusions: Phase 1 Germination Study 1. Riparian tree seed can be stored in freezers for at least two years after collection while maintaining greater than 80% viability. 2. Seed cleaning or storage in oxygen-free containers is unnecessary. 9

10 Phase 2: Greenhouse Studies of Soil Conditions, Seed Treatments, and Seeding Rates Primary Objective: determine the effectiveness of direct seeding under controlled conditions. Secondary Objectives: determine the effects of seed cleaning, soil compaction, soil texture, seeding rate, and organic fertilizer on tree establishment and growth. Desired high density of seedlings to mimic natural regeneration on the Bill Williams River National Wildlife Refuge. 10

11 Conclusions: Phase 2 Greenhouse Study Seed cleaning approximately doubled tree establishment. Soil compaction resulted in decreased growth rates. Sandy soil resulted in decreased growth rates (w/o organic fertilizer). Organic fertilizer decreased establishment rates, but increased growth rates in sand and compacted soils. Higher seeding rates resulted in increased establishment, but primarily in cottonwood. Fremont cottonwood dominated willow species. 11

12 Phase 3: Small-scale Field Study Overview 12

13 Phase 3 Small-scale Field Study Chronology 2007 Plots: Direct seeding a mix of Fremont cottonwood (20%), Goodding s willow (40%), and coyote willow (40%) discussed here and 2009 Plots: Direct seeding Goodding s willow alone: Different seeding and surface irrigation methods Variable seeding rates Results not presented here, but available by request. 13

14 Field Study Location 14

15 Small-scale Field Study Matrix (2007) Early-Time Sprinkler Irrigation Seeding Method Surface Irrigation Method Seeding Rate Plot Placement Three Weeks (Y) Hydroseed Un -Cleaned Seed (UH) Furrow (F) Block 1 (1) None (N) Hydroseed Cleaned Seed (CH) Broadcast Cleaned Seed (CB) Border (Small- Scale Basin) (B) Variable Block 2 (2) Block 3 (3) Notes: 1. Decreased proportion of Fremont cottonwood in seed mix, design seeding rate of 1350 PLS m Seeding Rate varied due to variable hydroseeding duration. 15

16 2007 Field Study Results: Four Months of Growth 16

17 Seeding Method Effects Results Seed Treatment Un-cleaned Hydroseed Cleaned Hydroseed Cleaned Broadcast Establishment, Stems m A B AB Fremont Cottonwood Above-ground Dry Biomass, g m -2 Least-squared Means and Significant Differences (Student s t-test) A AB B Hydroseeding (un-cleaned seed) resulted in highest cottonwood establishment. 17

18 Sprinklers by Surface Irrigation Treatment Early-Time Irrigation Surface Irrigation Method Saltcedar Density, Stems m -2 Fremont Cottonwood Density, Stems m -2 No Sprinklers Border Furrow 40.4 A 27.1 B 18.4 A 16.9 A Sprinklers Border Furrow 16.6 B 15.7 B 15.5 A 19.8 A Without sprinklers, furrow irrigation resulted in lower saltcedar establishment. Due to higher heterogeneity within border plots? Furrowing did not affect Fremont cottonwood establishment rates. Scaling effects? 18

19 Long-term Vegetation Observations: Crown Cover Over 3 Growing Seasons Crown Cover 100% Survey: 90% 80% 70% 60% 50% 40% 30% 20% 10% September 2007 May 2008 October 2008 May 2009 October % Fremont Cottonwood Saltcedar Grass and Sedge Shrubs and Forbs Vegetation Type 19

20 Conclusions: Phase 3 Small-scale Field Study 1. Cottonwood establishes well in field conditions and competes with weedy species. Establishment rate of 10.8% for un-cleaned hydroseed. 2. Willow species did not establish well: Establishment rate of less than 1% for all treatments. Due to low viability/establishment? Due to competition with cottonwood, grass, and/or saltcedar? Note: 2008 and 2009 studies indicated establishment of 1.5 to 3% for Goodding s willow. 3. Very high grass and saltcedar establishment compared to greenhouse studies. Note: greater growth and survival of cottonwood than saltcedar! 20

21 Study Conclusions and Recommendations Seed storage is not a limitation for riparian tree direct seeding. Soil conditions (bulk density, texture and fertility) should be analyzed in field restoration sites prior to seeding. Large-scale studies are needed to determine scaling effects and to conduct cost analyses. Fremont cottonwood will likely need to be seeded separately from willow species, or within seed mixes at very low rates. 21

22 Recommendations for Direct Seeding of Riparian Species Determine site soil salinity: Mitigation required if salinity is greater than ~3 ds/m. Maintain high soil water content during seed germination and seedling establishment. Control volunteer vegetation: Reduce the existing seedbank. Apply grass-specific herbicide during the first year. Manage seed dispersal (saltcedar specifically) near the site. Actively weed unwanted species during the first year. 22

23 Questions? 23