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Fire-adaptive traits in plants of tropical and subtropical grassy ecosystems have been the subject of considerable global research, but only recently studied in pyrogenic Florida subtropical grasslands. Plant growth forms, belowground organs, and post-fire recovery strategies were studied for 198 grassland specialists in peninsular Florida. Community types (dry-mesic, mesic, wet-mesic, and wet) were sampled with 1m2 plots along the edaphic-hydrologic gradient and the association between these variables and fire-related plant traits was tested using fourth-corner analysis. Caulescent herbs (43), cespitose graminoids (27), and rosette herbs (31) are the most common growth forms among species sampled. Plants with epigeogenous and hypogeogenous rhizomes dominate the sample plots, including matrix graminoids, shrub geoxyles, and an acaulescent rhizomatous fire-resilient palm (Serenoa repens). Most species (163; 82%) exhibit resprouting, including 30 facultative resprouters and 133 obligate resprouters. All woody rhizomatous species are obligate resprouters, and 35 ephemeral herbaceous species are obligate reseeders. Community type was a better predictor of species abundances than hydrology, however, hydrology was significantly associated with species traits measured, particularly rhizome texture, with woody rhizomes prevalent in all but the wet sites. Belowground organs (xylopodia, geoxylic suffructices) and growth form were associated with frequent fire and phylogeny, suggesting fire regime as a driver of community phylogenetic diversity. Persistence, rapid resilience and co-occurrence of geoxyles align Florida subtropical grasslands with other global geoxyle grasslands. The old-growth, pyrogenic grassy ecosystems of peninsular Florida are the center of geoxyle diversification on the southeastern US coastal plain. [ABSTRACT FROM AUTHOR]

Subtropical calcareous wet grasslands (SCWG) are pyrogenic hyper-seasonal grasslands with exceptional vascular plant biodiversity and conservation value in south-central Florida with floristic affinities to southern Florida marl grasslands, and both are dominated by Muhlenbergia sericea. We sampled 62 sites (n = 124 samples), of which 62 were surface soil samples (upper 1–10 cm), and 62 were subsurface soils (above the spodic horizon) across the edaphic-hydrologic gradient of savanna-grassland landscape in south-central Florida. We sought to determine how soil chemistry (17 variables) and texture (7 categories) might correlate with floristic composition and distinguish SCWG from savanna-grassland community types in peninsular Florida. To test which soil PCA axes were associated with plant community types, we used correlations between NMDS plot scores and the scores of significant soil PCA axes. Surface and subsurface soil chemistry were significantly correlated with dimensions of variation in savanna-grassland plant community types. In SCWG, soil chemistry is segregated because of higher Ca, pH, and percentage base saturation in subsurface soils. Lower cation exchange capacity, surface and subsurface soil texture with greater fine sand particles, lower silt, and higher clay content differentiate SCWG. Our results highlight the edaphic-hydrologic distinctiveness of SCWG, which supports previous recognition based solely on floristic and species composition, where calciphilic habitat specialists coexist with plants otherwise characteristic of brackish marsh, acidic grassland, and xeric sands. [ABSTRACT FROM AUTHOR]

Fire seasonality, an important characteristic of fire regimes, commonly is delineated using seasons based on single weather variables (rainfall or temperature). We used nonparametric cluster analyses of a 17-year (1993–2009) data set of weather variables that influence likelihoods and spread of fires (relative humidity, air temperature, solar radiation, wind speed, soil moisture) to explore seasonality of fire in pine savanna-grassland landscapes at the Avon Park Air Force Range in southern Florida. A four-variable, three-season model explained more variation within fire weather variables than models with more seasons. The three-season model also delineated intra-annual timing of fire more accurately than a conventional rainfall-based two-season model. Two seasons coincided roughly with dry and wet seasons based on rainfall. The third season, which we labeled the fire season, occurred between dry and wet seasons and was characterized by fire-promoting conditions present annually: drought, intense solar radiation, low humidity, and warm air temperatures. Fine fuels consisting of variable combinations of pyrogenic pine needles, abundant C4 grasses, and flammable shrubs, coupled with low soil moisture, and lightning ignitions early in the fire season facilitate natural landscape-scale wildfires that burn uplands and across wetlands. We related our three season model to fires with different ignition sources (lightning, military missions, and prescribed fires) over a 13-year period with fire records (1997–2009). Largest wildfires originate from lightning and military ignitions that occur within the early fire season substantially prior to the peak of lightning strikes in the wet season. Prescribed ignitions, in contrast, largely occur outside the fire season. Our delineation of a pronounced fire season provides insight into the extent to which different human-derived fire regimes mimic lightning fire regimes. Delineation of a fire season associated with timing of natural lightning ignitions should be useful as a basis for ecological fire management of humid savanna-grassland landscapes worldwide. [ABSTRACT FROM AUTHOR]