Restoration Solutions for Dryland Vegetation Management

Abstract

Drylands cover 40% of the Earth’s terrestrial surface, house over two billion people, and produce nearly half of all crops and livestock. These regions are critical for providing ecosystem services that support the entire global human population, but over 25% of drylands are already degraded. Active intervention and management through the form of ecological restoration can be used to slow, halt, or even reverse land degradation. In this dissertation, I present results from collaborative, applied research that is aimed at evaluating restoration solutions and providing restoration practitioners with the information needed to make data-driven, science-based decisions. In Appendix A, I review an emerging method of weed control that utilizes carbon as a soil amendment. Applying carbon in the form of sawdust or sucrose has been proposed as a strategy to suppress fast-growing, non-native plants and boost the competitive ability of slow-growing native plants in degraded ecosystems with elevated levels of soil nitrogen. I found that on average, carbon addition significantly reduced non-native weeds, but did not significantly alter the abundance of fast-growing plants. Based on the application rate of at least 210 g of carbon per m2 per year to suppress weed growth, I recommend carbon be used in the form of spot treatments rather than broadcast application. In Appendix B, I analyze the effects of rock detention structures on erosion control and promotion of plant growth using a 10-year case study. Installing rock detention structures increased the cover of grasses and forbs from 11% to 22% over ten years, and increased the drought resistance of shrubs, helping them to maintain stable cover throughout conditions of variable precipitation. Finally, in Appendix C, I examine weedy and native plant responses to large swings in precipitation following restoration seeding. In the Sonoran Desert, desirable species (seeded and non-seeded native species) exhibited a tolerance of about -20% to +25% precipitation deviation from average, indicating moderate flexibility, while weedy, non-native species proliferated during drought, and experienced the highest densities under the driest conditions. These trends were driven by the native volunteers (non-seeded) Lotus humistratus, Logfia arizonica, and Vulpia octoflora, and the non-native weeds Erodium cicutarium, Schismus barbatus, and Bromus rubens. The annual forbs Salvia columbariae and Lupinus sparsiflorus were the most successful seeded species, growing in 40–49% of the plots where they were seeded during very dry conditions, and 88% of plots where they were seeded in very wet conditions.