Background/Question/Methods Short-term restoration outcomes are variable, but little is known about outcomes 5 or more years after initial implementation due to limited funding and monitoring. Quantifying long-term outcomes of California grassland restoration is critical because it is expensive and because grasslands are important for fire resiliency, carbon storage and disproportionately harbor more rare species. A science-practice gap, where field research and management are not iterative, has been identified as a limitation to understanding and improving restoration outcomes. We surveyed 32 restored grasslands along a 1000-km N-S coastal gradient in California that were 3-30 years post-planting or seeding. In 2019 we quantified plant cover at species-level along multiple 50-m transects scaled to site size (0.5-15 ha) and resurveyed two-thirds of the sites in 2020. We analyzed all planning documents for each site prior to vegetation surveys. After field surveys, we conducted semi-structured interviews with one or more land manager from all sites. We set 25% native cover and 6 native species after 5 years as a standard performance metric to compare restoration outcomes across projects.
Results/Conclusions Overall, we found that most coastal grassland restoration projects in California reach the standard performance metric of 25% native cover and 6 native species after 5 years; specifically, 26 of 32 (82%) projects reached those targets, two projects fell within 5%, and four did not meet the metrics. Four projects (of 26) identified as successful were implemented <5 years ago but were >10% relative to the metrics. Ninety-four percent of projects were successful in achieving project-specific goals obtained from documents or interviews. Non-native plant cover was positively correlated with time since restoration, and non-native species cover was strongly negatively associated with native plant cover. Projects with more funding had higher species richness, but not necessarily greater native cover. Moreover, land managers agreed that the primary barrier to meeting restoration targets is limited funding which leads to shortcomings in non-native species management and long-term monitoring. Most land managers indicated they used a subset of the full grassland species palette for restoration. They select species that have a greater likelihood of germinating, surviving, and reproducing to achieve project-based goals. Many selected the same species across the 1000-km gradient which leads to a decrease in regional diversity and potentially ecosystem resilience. Overall, California coastal restoration projects succeed in meeting project-based targets but not in restoring the full species composition of the ecosystem.
