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The restoration of degraded ecosystems is one of the greatest environmental challenges of the 21st century. Dryland ecosystems are particularly difficult to restore once degraded and are home to large, socioeconomically marginalized human populations, heightening the need to improve current restoration practices. Though dryland restoration research efforts are accelerating, no evaluation of these efforts at a global level exists. The Global Arid Zone Project (GAZP) brings together an international research collaboration and has developed a global database of dryland restoration research projects. To-date, the project characterizes restoration outcomes on 365 sites, encompassing 1,825 treatments and 594,065 observations from 671 plant species. We asked how broadscale predictors affected restoration outcomes, focusing on factors such as seed inputs, species traits, abiotic site conditions and management treatments, and their relationships with success, measured as the probability of species occurrence in treated areas. We also compared the motivation for restoration efforts world-wide, and described several stand-out examples of successful dryland restoration. Of the 11,816 observations in this database, the majority were either not at all successful (0% seedling establishment, 68% of the database) or completely successful (100% seedling establishment, 8% of the database). Restoration success varied widely among projects and sites, and random factors (i.e., unmeasured site-specific conditions) explained much of the variance in success. However, global patterns of restoration success emerged. Seeding rate was a major predictor of success: across projects, sites, and species, success rates exceeded 75% whenever seeding rates were higher than 1,200 seeds m-2, but 84% of projects used rates less than 500 seeds m-2 per species. Site aridity also affected outcomes: predicted success rose from ca. 31% to 54% as site aridity index decreased from 0.1 (highly arid) to 0.4 (less arid), then rose more gradually from ca. 54% to 64% between an index of 0.4 to 0.7 (low aridity). Surprisingly, while invasion was a major motivation for restoration, weed control only increased predicted probability of restoration success by 10%. Together, our results quantify several of the factors driving variable levels of restoration success around the globe for the very first time. The GAZP network provides a new opportunity to learn from successes and failures and improve future restoration efforts.
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Presented by Daniel Winkler and Nancy Shackelford
Daniel Winkler is a plant evolutionary ecologist studying how populations respond to global climate change. He is a Research Ecologist with the U.S. Geological Survey's Southwest Biological Science Center, working closely with the BLM's Native Plant Program and National Park Service.
Nancy Shackelford is a restoration scientist who has trained as a community ecologist and data analyst. She has worked in a wide range of global ecosystems, but focuses primarily in grasslands of all sorts, from prairies to drylands.
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