Abstract: Flowering likely plays an important role in determining the long-term recovery of plant communities after fire. Plants with different growth forms could have different resource allocation strategies post fire, prioritizing either vegetative growth or flower production to maximize fitness, and many may not flower in the immediate years after fire. Previous studies on post-fire recovery in southern Californian shrublands have mainly focused on vegetation, but little is known about whether conclusions from vegetation directly translate into the flowering community. In this study we compared flower abundance, diversity, size, and community composition in coastal sage scrub (CSS) at different post-fire stages. We collected data during the 2021 and 2022 flowering seasons from 22 CSS transects in three post-fire categories across Orange County: recent burn (2020), intermediate (2017), and unburned ( >10yrs). We recorded all species flowering within 1m of the 50m linear transects, and counted all flowers within 1m2 quadrats distributed every 5m along transects. We also photographed flowers in the field against a scale and determined length and area using ImageJ. Transect flower diversity, abundance, and flower size for individual species were analyzed using linear mixed-model methods, while community composition was assessed through constrained ordination methods.
Recently burned sites had higher flower diversity and species richness, similar to previous findings of higher vegetation diversity following fire. Higher raw flower abundance in 2022 was driven by mass-flowering species such as Salvia mellifera in unburned and Acmispon glaber in intermediate sites. However, flowering intensity (# flowers/vegetation area) showed little difference among burn categories, suggesting that the high flower abundance is a direct result of increased plant size. Flowering community composition differed among the three post-burn categories, with recently burned transects composed of more flowers from native and non-native forbs in the first post-fire years, as well as increased presence of fire following species such as Phacelia parryi. Flower size did not differ among post-burn categories for most species, but Salvia mellifera was an exception, with significantly larger flowers in recently burned transects. Overall, flowering patterns after fire largely followed the same patterns gathered from post-fire vegetation studies. The results suggest that future studies of recovery after fire in CSS could often rely on initial post-fire vegetation cover alone, with the caveat that a few changes in flowering intensity and flower size could be missed, especially for shrubs.
