Resistance and resilience: ten years of monitoring shrub and prairie communities in Orange County, CA, USA

Abstract

Mediterranean‐climate natural systems have high ecological value, yet the extent of their cover has diminished greatly due to changes in land use. Other stressors, ranging from intense short‐term disturbances such as wildfire to more gradual events such as extended drought and continuous pressures including competition with invasive species, test the resistance and resilience of community composition and structure. Data from long‐term monitoring provided an opportunity to evaluate the responses of three Southern California plant communities (chaparral, coastal sage scrub, and grassland) to disturbances. We analyzed ten years of point intercept and quadrat data from Orange County to describe trends through time and assess community resistance and resilience. We found that grassland communities, which were more degraded from the start of our study, were generally resistant to change. Chaparral was also fairly resistant to disturbance, while coastal sage scrub exhibited more variation, with some transects exhibiting more resilience than others. Transects with fewer native shrubs experienced less of a decline in shrub cover during drought than those with dense shrubs. Grasslands had the lowest native diversity. There were increases in native diversity in years with more precipitation that were preceded by dry years. There was a decline in native perennial bunchgrasses during our monitoring. Our analyses demonstrated the resilience of native shrub cover to fire and the susceptibility (low resistance) of dense native shrubs and native grasses to drought and increases in non‐native species. We encourage academic ecologists to embrace diverse data sources available for hypothesis testing, especially monitoring efforts associated with regulatory purposes, to advance the goal of understanding long‐term dynamics.

Non-native plant removal and high rainfall years promote post-fire recovery of Artemisia californica in southern California sage scrub

“…Moreover, most previous southern California post-fire research followed large-scale burns in 1978 and 1993, before the onset of recent intense drought conditions (but see [34]). While a few studies document the importance of water availability to native shrubs in sage scrub [35], none have yet developed statistical models that link rainfall with shrub demographic rates.…”

Warming as a Driver of Vegetation Loss in the Sonoran Desert of California

“…Studies of the importance of time lags between precipitation occurrence and vegetation response have often indicated that the legacy of precipitation in prior years influences productivity and other ecosystems processes in the present (Bunting et al., 2017; Kimball et al., 2018; Ogle et al., 2015; Sala et al., 2012). We observed this type of legacy effect in the Landsat record (Figure ), and that the importance of precipitation legacy increased at longer timesteps, underscoring the importance of long‐term precipitation regime in driving vegetation trends.…”

Water availability affects the relationship between pollen intensity and seed production

“…5B ). Thus, we predict the distance from a patch of the highly invasive B. nigra ( Bell and Muller 1973 ) may have a greater impact on seed set in wet than in drought years, all else equal, as these southern California coastal sage scrub communities swing between precipitation extremes ( Kimball et al 2018 ).…”