Dynamics of gaps, vegetation, and plant species with and without fire

Abstract

PREMISE OF THE STUDY: Areas lacking dominant plants, or gaps, can support high diversity and specialist species. Previous chronosequence research in Florida rosemary scrub showed indistinct gap area patterns with fire and the dependence of certain species on gaps. We hypothesized that fire and gap size would affect extinction, colonization, diversity, and vegetation composition. M ETHODS: In 2011-12, we revisited gaps first sampled in 2003, recording vascular plant and ground lichen occurrence by species, gap area, and burn history. We analyzed gap, vegetation, and species dynamics using linear mixed models, with Florida rosemary scrub patch as a random factor. K EY RESULTS: Gap areas declined quickly during the first 10 yr postfire and then stabilized. Between 2003 and 2011-12, unburned gaps usually remained extant or split, whereas burned gaps usually merged. Unburned gaps tended to shrink, whereas burned gaps became larger. Species richness was positively related to gap area, fire, and their interaction. Over time, richness declined in unburned gaps and increased in burned gaps. Local extinction and colonization of individual species were related to fire between 2003 and 2011-12. In burned gaps, ground lichens disappeared, but many herbaceous species, including those killed by fire, increased occupancy. Colonization of most species was favored by burning, large gaps, or both. CONCLUSIONS: In Florida rosemary scrub, fire and increasing gap size increased species richness and many individual species occurrences, reduced local extinctions, and increased colonizations. Therefore, land management activities that encourage the creation and maintenance of large gaps will promote biodiversity in this system.