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Identifying barriers to successful establishment of post-fire seeding in the Great Basin

Kulpa, Sarah M

Titre : Identifying barriers to successful establishment of post-fire seeding in the Great Basin

Auteur : Kulpa, Sarah M

Université de soutenance : UNIVERSITY OF NEVADA, RENO

Grade : Master of Science (MS) 2010

The shift of Great Basin ecosystems from diverse shrub-grass communities to near monocultures of annual grasses has altered ecosystems, caused more frequent and intense fires, and led to an increased demand for plant material that can restore altered landscapes back to complex, diverse systems. The Bureau of Land Management (BLM) in Nevada currently spends millions of dollars through the Emergency Stabilization and Rehabilitation (ES&R) program each year to re-seed land affected by fire. Seeds used for revegetation face many barriers that often prevent their successful establishment in this semi-arid environment including precipitation and temperature limitation, competition with invasive species, and soil type. Field surveys were done to monitor revegetation patterns between years and across aspects at five fire sites in Elko County, NV. A novel common garden experiment was conducted to determine what plants traits increase establishment success in invaded, post-fire field sites. We collected seeds from drill seeded populations of Elymus elymoides ssp. californicus (Toe Jam Creek bottlebrush squirreltail) at two fire locations in Elko County, NV. Seeds were planted in a common garden environment, where we compared the phenology, size, and reproduction of surviving plants to those of the original restoration material.In our field survey study, we found that vegetation structure within a site changed significantly in the short distance separating flat, north and south facing aspects ; Bromus tectorum (cheatgrass) was more likely to establish on south aspects, residual grasses were more likely to remain on north aspects, and seeded perennial grasses were more likely to establish on flat areas. Over time, the density of B. tectorum and non-seeded perennial grasses and forbs increased, whereas the density of seeded perennial grasses and forbs decreased. We found that for both seeded and residual perennial grass, plant density in 2007 was a good predictor of the plant density in 2009. The density of B. tectorum in 2007 also predicted the density of B. tectorum in 2009, but not as strongly as perennial species. In our common garden experiment, plants grown from the original restoration material were larger, produced larger and more seeds, and produced seeds later in the season, while plants grown from material that successfully established at the restoration sites were smaller, produced smaller and fewer seeds, and produced them earlier. Differences in seed size were observed at the family level and persisted in the common garden environment through the next generation, indicating that seed size is likely a genetic, rather than maternal environment, effect. These results were consistent across two different field sites. Natural selection, rather than genetic drift, is the most likely explanation for trait shifts observed in established seed material, and these results indicate that smaller plants may be better adapted for establishment in arid environments. Our results suggest that altering current monitoring and seed production techniques may increase restoration success in the Great Basin. Modifying management objectives, seed mixes, and seeding efforts for slope-aspect and pre-fire site conditions may result in more cost effective and successful restoration. Restoration practices may also be improved if plant developers select for traits that perform well at restoration sites, rather than in controlled, production environments.

Mots clés  : cheatgrass Elymus elymoides fire Great Basin restoration seed size


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