Biotic and Abiotic Barriers to Dryland Restoration

Karban, Claire Curry

Graduate Thesis Or Dissertation

Biotic and Abiotic Barriers to Dryland Restoration Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/8336h3498

Abstract

Drylands cover ~45% of Earth’s land surface and up to 20% of drylands are severely degraded. Land degradation results in the long-term loss of important ecosystem services and functions such as grazing and cropland, soil fertility, soil stabilization, erosion prevention, primary productivity, and biodiversity. Once degraded, recovery often either does not occur, or occurs too slowly to be relevant for management. In these cases, active restoration is required to restore ecosystem services and functions. Despite the tremendous need for dryland restoration, success is elusive. About 17% of seedings failing to establish any plants and over 90% of seeds used in restoration fail to recruit.

My dissertation looks at biotic (propagule scarcity, granivory, competition) and abiotic (harsh climate, destabilized soils) barriers to restoration in severely degraded drylands. My first chapter investigates the role of granivory in limiting seeded restoration. I find that harvester ants can remove up to 80% of seeds, significantly reducing the number of native seeds in the seedbank. However, foraging behavior occurs primarily in late spring through early fall. Increasing seed germination during the first growing season would protect seeds from ant granivory. In the second chapter, I test several methods to create microsites and stabilize soils while maintaining active grazing. The shifting nature of restoration barriers meant that we were not successful in setting the site on a positive trajectory towards recovery. This project highlights the importance of adaptive management and the need to be realistic when it comes to restoration outcomes under a changing climate. My third chapter investigates microsite limitation in dryland restoration by creating microsites with soil pitting, biochar, and seed pellets. I find that soil pitting and biochar increase native plants, but they also contribute to even larger increases in non-native vegetation. The barriers presented by dryland restoration remain clear throughout this work, as does the importance of continuing to improve our practical understanding of dryland restoration.

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