Researchers:
Kristen Pekas, Ecology M.S., 2010, Utah State University
Gene Schupp
Study Dates:
Summer 2006 to Spring 2009
SageSTEP Study Plots:
Study Design and Objectives:
This study examined the relationship between soil seed pools and aboveground vegetation in areas threatened by cheatgrass invasion as well as the impacts of prescribed fire on seed pools.
Data were collected an analyzed to address the following questions:
- What is the relationship between the seed pool and the aboveground vegetation?
- Does prescribed burning affect the seed pool species composition and abundances?
- Does cheatgrass abundance influence the seed pool composition?
Methods:
- Line-point intercept data was used to quantify the presence and relative abundance of species aboveground, and seed pool samples were collected before and after prescribed fire from control and burned plots.
- Seed pool soil samples were collected before and after prescribed fire from subplots defined as phase 1 (least invaded by cheatgrass) and phase 3 (most invaded by cheatgrass).
- 11 soil sample points were randomly selected along 4-30m transects per subplot.
- Soil samples were cold-moist stratified for 60 days to initially break dormancy.
- Seed pools were evaluated by direct germination in a greenhouse; samples were kept moist.
- Seedlings were identified, counted and removed.
- After 115 days, samples were dried out, mixed, rewatered and emergence was censused for an additional 21 days.
- Individuals that were not identified as seedlings were transplanted and grown to maturity.
Results:
Researchers found that the seed bank and aboveground vegetation shared 19 of 71 species. Relative abundances of these shared species were similar except that desert madwort (Alyssum desertorum) and bur buttercup (Ceratocephala testiculata) had significantly higher quantities in the seed bank compared with aboveground abundance, and sagebrush (Artemisia tridentata) was significantly more abundant aboveground than in the seed bank. Species that were found either only in the seed bank or only in the aboveground vegetation were all at low abundances.
Although prescribed burning did not alter species composition, it did affect the abundance of some species in the seed bank. Fire reduced the abundance of cheatgrass seeds, especially beneath shrubs. Fire also reduced the densities of bur buttercup and Sandberg bluegrass (Poa secunda) seeds. While Sandberg bluegrass seed densities remained low one year following the burn, it appears that bur buttercup densities can recover quickly.
As has been found in other studies, the seed bank was highly variable in density and composition. Surprisingly, the abundance of cheatgrass seeds was not related to phase. Although phase 1 and phase 3 seed banks were similar overall, phase 1 communities were slightly more diverse and had significantly higher densities of seeds, especially of seeds of perennial grasses, than did phase 3 communities.
This study indicates that understanding the role of seed banks in restoration of sagebrush communities can aid management decisions. Where possible, knowing the seed bank contents in a project area, and incorporating this information into management decisions could improve project success rates. Additionally, managers should consider the potential impacts of management activities on seed stores.
Conclusions:
- The seed pool and aboveground vegetation were moderately similar before fire.
- Fire did affect the seed pool composition and altered the relative abundances of a few annual species.
- The abundance of cheatgrass aboveground was reflected in the seed pool. Communities with low cheatgrass abundance were slightly more diverse. However, seeds of many species were more abundant in communities with higher cheatgrass abundance.
- Land managers and restoration practitioners should consider these effects on the seed pool when making management decisions.
References:
Pekas, K.M. 2010. Seed Pool Dynamics of a Great Basin Sagebrush Community in the Context of Restoration. MS Thesis, Utah State University, Logan, UT. Available here.
Pekas, K. and G. Schupp. 2009. Seed pools, aboveground vegetation, and prescribed fire in the context of sagebrush restoration. Intermountain Graduate Research Symposium, Logan, UT, April 1, 2009. Poster available here.