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University of California Santa Barbara (2021)

Restoring Native California Grasslands in a Changing Climate

Nolan, Madeline Pinsonneault

Titre : Restoring Native California Grasslands in a Changing Climate

Auteur : Nolan, Madeline Pinsonneault

Université de soutenance : University of California Santa Barbara

Grade : Doctor Philosophy (PhD) in Ecology, Evolution and Marine Biology 2021

Résumé partiel
Over the last two centuries, there has been a dramatic shift in the composition of grassland communities in California due to anthropogenic disturbances, the cessation of Native American burning and invasion by exotic species. As a result, the majority of grasslands in California are dominated by exotic annual grasses and forbs, with native species making up only a small fraction of the cover at most sites. These exotic dominated grasslands also tend to persist despite the cessation of the disturbances that created them (agricultural tillage, livestock grazing) rather than convert back to perennial communities suggesting that active restoration will be required to reestablish native grassland communities. My dissertation seeks to improve restoration outcomes in California grasslands by exploring the mechanisms that influence the establishment and persistence of native grassland species during restoration and how climate change is likely to interact with these mechanisms. I began with a meta-analysis of previous restoration research to understand if there were certain restoration techniques that consistently improved native plant establishment in grassland and sage scrub ecosystems across California. I categorized techniques by the constraint they addressed (dispersal, abiotic, or biotic) to determine which restoration practices are more likely to improve plant establishment. I explored the impact of these practices on whole communities and on different functional groups (grass, forb, and shrub). In total, I analyzed establishment success in 53 studies and found that in grassland and sage scrub communities addressing the dispersal filter (seed availability at the site) is the best way to improve plant establishment regardless of functional group. This suggests that most native plants targeted in restoration are seed limited and thus adding seeds or seedlings will lead to the greatest improvement in establishment compared to other restoration techniques. Native plant establishment can also be affected by the seed provenance, with many practitioners restricting seed collection to local areas near to a restoration site. This restoration technique, termed “local seed collecting”, is practiced because it is assumed that most plants are adapted to local environmental conditions. There is however, considerable debate about whether local seed collection should be the default seed sourcing strategy as the effects of climate change are increasingly considered in restoration planning. It is especially important to explore whether local seed sourcing is necessary for dominant species often used in restoration. One such species is Stipa pulchra, a commonly planted perennial grass in California projects that is extant across a wide geographic range. In my second chapter, I explore how different seed sourcing strategies affect the establishment and growth of S. pulchra. I established three common garden plots distributed across a latitudinal gradient in California, and into them I planted seeds collected from seven distinct populations of S. pulchra. I then monitored their growth and reproduction for two years. I found limited evidence that restricting seed collection to local populations of S. pulchra resulted in higher performance than using seeds from more distant populations. Instead, I found evidence to support an admixture seed sourcing approach as a way to increase resiliency to environmental variation.

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Page publiée le 7 décembre 2021