Interactive Effects of Fire and Microhabitat on Plants of Florida Scrub

Fire, microhabitat, and their interactions affect Florida scrub ecosystems and their plant species. Concepts of vegetation change in the Florida upland landscape have followed successional theory, with recent models emphasizing the resilience of Florida scrub to fire and the interactive effects of the vegetation and fire regime. We extend these models by incorporating greater complexity in vegetation types and emphasizing that departures from modal fire frequencies may alter vegetation. In particular, fire exclusion leads to structural and compositional changes that, in turn, alter vegetation changes following the reintroduction of fire. Individual species responses to fire can be categorized by the demographic mechanisms of the response (e.g., resprouting, clonal growth, seedling recruitment) and by typical patterns of abundance during fire-free intervals. Various types of scrub differ in these life-history traits. For example, xeric rosemary scrub supports more herbs, more endemics, more specialized species, and more seeders increasing in abundance between fires as compared to less xeric scrubby flatwoods. Several of these species are demonstrated specialists for gaps, which are more abundant and persistent in rosemary scrub than in scrubby flatwoods. In scrubby flatwoods, patterns of species abundance are explainable by time since fire and the presence of gaps, and sprouters are more successful than seeders between fires. In rosemary scrub, where gaps remain long after fire, species abundance patterns reflect only gap abundance, and seeders are especially successful between fires. Because fires create or enlarge gaps that are then closed between fires (especially in less xeric habitats), gap specialists may be sensitive to both fire and microhabitat. Alteration of the modal fire regime is hypothesized to affect the proportion of sprouters and seeders, microsite diversity, and the long-term local persistence of species with different specializations for postfire response and between-fire competitive abilities. Metapopulation dynamics in a landscape patterned by edaphic gradients, a patchy and variable disturbance regime, and small-scale gap dynamics produce varied spatial and temporal patterns in species’ abundances.