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Assessing regional outcomes and drought adaptation management strategies for coastal California grassland restoration

Creative Commons 'BY-NC-SA' version 4.0 license
Abstract

Planetary health has been an increasing concern as the climate and biodiversity crises continue to worsen. Ecological restoration has been suggested as a land practice that could simultaneously mitigate and assist in recovering from these crises. Despite large expenditures supporting grassland restoration and numerous completed projects to date, there has been no systematic assessment of post-implementation outcomes and only a few projects consider which species are most likely to successfully establish in changing climatic conditions. Plant trait characteristics can help elucidate mechanisms that allow certain species to survive and can provide information about which species will have higher mortality risk in response to drought. This could aid with species selection for planting efforts in ecological restoration. I combined approaches ranging from organismal physiology to regional restoration to evaluate grassland restoration outcomes and guide how to adapt management for increasingly arid conditions in California. I assessed the responses of phylogenetically diverse plant communities and found that key functional traits and evolutionary relationships explained plant mortality. Traits that helped plants withstand drought such as higher leaf lobedness and slower growth rates reduced the risk of plant mortality. Phylogenetics indicated that related species experienced lower mortality risk, suggesting that the plants may have similar traits that work towards surviving similar abiotic filters. In greenhouses, I showed that functional traits for plants in this region were shaped more by drought stress than competition with invasive species. Using vegetation surveys, management interviews, and document analysis of 37 restored coastal grasslands spanning a 1000-km north-south gradient, I found that most restoration efforts achieved project-based goals. However, management interviews suggest that preferential use of a few highly successful species may facilitate future biotic homogenization, thereby reducing regional plant richness. Although my research suggests certain species are ideal for restoration during drought, the survey analysis suggests a need for management to balance the use of native species that establish and grow better versus recovering regional plant diversity.

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