Fire and Flood: Why Are South-central Florida Seasonal Ponds Treeless?

Abstract

While seasonal ponds in the scrub landscape of the Lake Wales Ridge in south-central Florida are favorable for establishment of small south Florida slash pines (Pinus elliottii var. densa), few seasonal ponds have mature trees. We hypothesize that disturbances (fire and/or flooding) periodically exclude trees from seasonal ponds. We studied the demography of slash pines in relation to water level and fire for a decade from 1992–2001 in four seasonal ponds, two with long and two with short hydroperiods. Seasonal ponds were favorable for pine growth (0.1–0.6 m increase in height annually, growth from grass-stage to one meter in about 7 y) and annual survival (survival generally over 80% in years without fires). Most recruitment (appearance of seedlings in a “grass stage”) occurred in drier ponds. Flooding episodes occurred in most years and lasted 3–11 mo. Mortality increased with flooding intensity (summed flooding depth) in 3 of 9 y and was concentrated in pines <1 m tall. Growth rates were unaffected by flooding. A low-intensity prescribed fire created 72% mortality, while a large intense wildfire caused nearly 100% mortality. Although South Florida slash pine can survive short-term flooding and moderately intense fire, both flooding and fire can exclude trees from many seasonal ponds. Fire was a stronger force during our study. Seasonal ponds in south-central Florida are usually treeless not because conditions are generally unfavorable for growth and establishment of south Florida slash pines, but because episodic flooding and fire cause massive mortality of seedling and sapling pines.