UC Irvine

Post-fire recovery in terrestrial ecosystems is a complex, long-term process with outcomes that depend on the interaction of abiotic and biotic factors before and after fire. Understanding these processes helps to inform conservation efforts so that these natural ecosystems and the services they provide may be preserved. With anthropogenic activities changing fire regimes worldwide, there has been increasing interest in investigating the dynamics of recovery post fire. While comparisons of vegetation at different stages post fire are well documented, less is known about recovery in the form of comparisons of post-fire vegetation to pre-fire stands. Furthermore, recent fire history can not only affect vegetation cover, but also flowering and pollinator interactions. These effects on flowering and pollination should also be examined to better understand recovery patterns in the long-term. The first chapter examines vegetation recovery in two southern California ecosystems through a long-term (15Y) monitoring dataset and compares pre- and post- fire differences in plant community composition with chronosequence differences from the 2017 canyon 2 fire. Burned areas in coastal sage scrub had lower native shrub cover and greater forb cover, along with higher vegetation diversity from greater forb diversity, with changes in species composition persisting four years after fire. In contrast, vegetative cover recovered quickly in grasslands. The inclusion of pre-fire data allowed identification of a pre-existing difference in non-native grass composition between grassland field sites that would have otherwise been interpreted as a direct effect of fire. These results demonstrate the importance of long-term monitoring to allow for the separation of the effects of disturbance vs pre-existing differences. The second and third chapters focus on flowering and pollination in coastal sage scrub. I sampled 22 transects with three burn statuses (recent = 0.5-1.5 y after fire, intermediate = 3.5-4.5 y after fire, and old burned = >10 y after fire) across two years. Chapter 2 explores how recent fire history affects flowering abundance, diversity, and flower size. Recent burn history increased flowering diversity and affected flowering community composition, but in a way that was mostly predicted by vegetation recovery rather than changes in flowering patterns, suggesting vegetation can serve to predict flowering diversity and composition. Flower abundances differed across the two sampling years rather than burn statuses, and most species showed no change in flowering intensity after fire. The third chapter explores how recent fire history impacted flower visitation by pollinators and pollen deposition. Burn status alone had little effect on pollinator visits, with visits and number of visitors strongly associated with flower abundance per area observed. Differences across burn statuses and year did impact how pollinator visits increased with flower count. Types of pollinators also differed, with Apis mellifera, the most common visitor, showing the greatest increase in visits in relation to flower count. Pollen deposition on five common flowering species (Salvia mellifera, Gilia angelensis, Eucrypta chrysanthemifolia, Hirshfeldia incana, Erodium cicutarium) was mostly not affected by burn status, expect for conspecific pollen deposition in S. mellifera, which was higher in intermediate burn sites. Overall, we saw that while grasslands recovered quickly in both cover and composition, coastal sage scrub remained changed for longer after fire. Increased forb diversity in CSS after fire contributed to increased flowering diversity, and though effects of burn status on pollinator diversity were not directly detected, we did find an increase in pollinator diversity with increased flowering diversity at our sites. However, overall flowering abundances and their positive effects on pollinator visits were impacted by the annual changes in flower production in native forbs and shrubs, and less clearly associated with recent burn history. Combined, these chapters help to highlight facets of post-fire recovery beyond burned/unburned comparisons and vegetation recovery, including the importance of separating the effects of burn from pre-fire community differences, and impacts of flower number on pollinator visits.