Gap ecology in the Florida scrubby flatwoods: effects of time-since-fire, gap area, gap aggregation and microhabitat on gap species diversity

摘要

Questions: The ecology of landscape gaps is important for the maintenance of species diversity in a variety of plant ecosystems. In the scrubby flatwoods community type of the pyrogenic Florida scrub, we aimed to identify the relationship between time-since-fire, gap area, quality (microhabitat) and aggregation (structural connectivity) with neighbouring gaps on gap species diversity and occupancy.Location: Archbold Biological Station (ABS), Lake Wales Ridge, south-central Florida, USA.Methods: We measured species diversity, gap area, aggregation and microhabitat (percentage bare sand) in 120 gaps divided evenly amongst 1, 2, 4, 8, 16 and 26 yrs since fire in the scrubby flatwoods of ABS (typical fire return interval of 5-20 yrs) throughout the summer of 2011.Results: Gap area and aggregation were significantly highest in the first 4 yrs after fire, but decreased and remained fairly constant at longer times-since-fire. Percentage bare sand gradually decreased with time-since-fire until a strong decline at the 26-yr mark, where litter cover was significantly higher than all previous years. Gap area strongly and positively predicted species richness (total and herb spp.) and total species diversity (H'). Bare sand content was positively correlated with the richness of species that are obligate seeders post-fire. Gap aggregation was generally a poor predictor of diversity components, although it positively influenced the occurrence of Stipulicida setacea, a seeder species that occasionally resprouts after fire. Overall, species richness and diversity peaked at intermediate times-since-fire, probably because long-unburned gaps were too small and inundated with litter to sustain higher richness of herbs and obligate seeders.Conclusion: In a prior gap ecology study, in neighbouring more xeric rosemary scrub, gaps were larger, more persistent and had higher bare sand cover, resulting in higher levels of total species richness and diversity for decades longer after fire than gaps in this study. In both these types of Florida scrub, the threat of fire suppression and its adverse effects on gap area and microhabitat may be detrimental for several endemic species that depend on gaps