Florida scrub is a fire-maintained shrub vegetation of well-drained, sandy soils; dominant species include several species of Quercus and Serenoa repens. This shrubland is unique to Florida and supports many rare plants and animals. Most scrub has been lost to urban and agricultural development. Scrub vegetation is associated with ridge systems that originated as coastal dunes and soils are typically highly leached, acidic, and low in nutrients. On some aggrading barrier islands, scrub occurs on younger soils with shell material that results in neutral to alkaline soil pH. The Cape Canaveral-Merritt Island barrier island complex in east-central Florida supports dune ridges that range from relatively recent to > 30,000 years old with a range of soil leaching and reaction. Between 1992 and 2005, we sampled 30 stands of long-unburned scrub across the barrier island complex with 196 line-intercept transects (15 m length) and recorded community composition in ≤ 0.5 m and > 0.5 m strata. We determined mapped soil type for all transects; for 151 transects we determined soil pH of the 0-15 cm and 15-30 cm layers.
Results/Conclusions
Hierarchical cluster analysis of stands (N = 30) and transects (N = 196) using 41 species (of 53) present in ≥ 2 transects gave two groups: coastal scrub with Quercus virginiana (shrub form) and Serenoa as dominant species on the most alkaline soils, and oak-saw palmetto scrub with Quercus chapmanii, Q. geminata, Q. myrtifolia, and Serenoa on the strongly to somewhat acidic soils. Myrcianthes fragrans occurred only on alkaline soils, and ericaceous shrubs only on acid soils. Soils show a progressive leaching of shell material from the surface horizons followed by podsolization; this process takes ca. 4000 years. Non-metric multidimensional scaling (NMS) ordination at the stand level separated the two groups along the first axis. NMS ordination of the transect data showed the gradient of coastal to oak-saw palmetto scrub. Position of transects on the first axis was related to soil pH class, rs = -0.793, p < 0.001 (soil series coded as acid, neutral, alkaline) and to measured pH of the 0-15 cm layer (rs = -0.616, p < 0.001) as well as to pH of the 15-30 cm layer (rs = -0.623, p < 0.001).