Post-fire resilience of restored coastal sage scrub and grassland communities

California coastal sage scrub (CSS) and native grassland systems are experiencing increased fire frequencies and extreme droughts due to climate change. These stressors, in addition to historical and ongoing disturbances, make native-dominated communities vulnerable to vegetation-type conversion to communities of non-native grassland. The challenge is to restore resilient native plant communities under these shifting conditions. Our study site, Bee Flat Canyon in the Santa Ana mountains, contains CSS, grasslands, and other plant communities degraded by historic agricultural and rangeland use. The area was restored by the Irvine Ranch Conservancy (IRC) over 10 years and burned shortly after project completion in the 2020 Silverado fire, presenting a unique opportunity to assess restoration resilience to fire. We studied how restored CSS communities recovered compared to unrestored degraded and intact areas post-fire, whether physiological traits influence post-fire cover of CSS species, and how restored grassland changed over time in relation to temperature, precipitation, and fire. We found no significant difference between restored and intact CSS sites for abundance and survivorship of crown sprouting shrubs and cover of native/non-native forb seedlings, indicating that restored sites were as resilient as intact sites. Degraded sites remained in a degraded state post-fire and contained almost zero native shrubs. There were differences in CSS plant community composition amongst degraded, intact, and restored CSS sites such that restored sites contained some native species that were seeded but absent from intact sites and vice versa. Plant physiological traits did not correlate with cover of CSS species, indicating that traits were not predictors of fire response. In restored grassland, cover did not significantly correlate with temperature and precipitation. Forbs and non-native grasses recovered post-fire, but the native grass Stipa pulchra continued to decline, possibly due to competition. Grassland plant community composition shifted significantly toward a higher dominance of non-native grasses in the second year post-fire compared to previous years, indicating a need for non-native control measures after fire. From these assessments, we recommend the IRC to (1) continue monitoring and managing weeds in CSS and grasslands, (2) enhance the diversity of their restoration seed mixes with additional native species, and (3) develop a post-fire recovery plan to limit the reestablishment of non-native species and support resilience of native species.