Predictors of species richness in northwest Florida longleaf pine sandhills

Soil characteristics, disturbance histories, and species richness among distinct groups of plants and animals may be useful predictors of important conservation areas when data are limited. We used multivariate analysis of covariance to test the hypothesis that the species richness of plants, arthropods, herpetofauna, and breeding birds are correlated and increase with soil fertility (silt and clay content in sandy soils), soil variability, and hardwood midstory reduction in subxeric, nutrient-poor longleaf pine sandhills at Eglin Air Force Base in northwest Florida. During 1994-1995 and 1998-1999, we sampled 30 81-ha plots with varying fire-exclusion histories and at two spatial scales of resolution (10 x 40 m and 81 ha). The relationship between the number of plant species and percent silt and clay and its coefficient of variation was significant and positive at the plot level (81 ha) but not at the subplot level (10 x 40 m). Herpetofaunal species richness was the only faunal variable that increased with silt and clay content, but the coefficient of variation did not. Multivariate effects of hardwood reduction were significant in 1998-1999 but not in 1994-1995, which suggests that the reintroduction of fire increased species richness across taxa. Univariate effects of hardwood reduction were marginally significant for plant species richness at the subplot level and not significant for herpetofaunal species richness at either scale. Plant and arthropod species richness were not correlated. Herpetofaunal species richness was not correlated with that of other taxa (plant and animal). The species richness of plants and arthropods were each significantly positively correlated with the richness of breeding bird species at the subplot level during 1994-1995, whereas only arthropod species richness was positively correlated with bird species richness at the plot level in either year. Our results suggest that the restoration of fire regime may be the most effective tool with which to increase diversity in pyrogenic areas considered for conservation protection.