Soil properties drive differences in taxonomic groups among pine forests of the Atlantic coastal plain

Background/Question/Methods

The pine forests of the Atlantic coastal plain have undergone substantial changes in the composition and diversity of both plant and avifaunal communities as a result of human activities. Many native plant species within this ecosystem require bare, mineral soil for germination, yet decades of fire suppression has resulted in the accumulation of leaf litter, soil organic matter, and a dense hardwood mid-story. Such changes inhibit the regeneration of longleaf pine and its diverse array of associated species, and these changes in plant community composition may lead to changes in the composition of organisms in other taxonomic groups. To ascertain the influence of soil characteristics on the composition of different groups of organisms, we collected data on soil properties and the community composition of plants, arthropods, and breeding birds across a gradient of soil characteristics in a series of mature (53-80 years old) pine stands. Based on these data, we developed a structural equation model (SEM) to determine the influence of soil properties on the composition of plant, arthropod, and breeding bird communities. Of particular interest is the sensitivity of native avifaunal species to soil-driven changes in plant community composition, particularly among species of concern such as the Red Cockaded Woodpecker (Picoides borealis) and the Bachman’s Sparrow (Aimophila aestivalis).

Results/Conclusions

The relationship between soil characteristics and plant species richness and composition was quite strong, as was the relationship between vegetation composition and breeding bird composition. However, arthropod composition was not a good predictor of breeding bird composition. Nevertheless, we found some evidence that the specimen abundance of certain arthropod Orders was significantly related to measurements of the breeding bird community. The abundance (quantity) of Araneae (spiders), for example, was significantly related to bird species richness, and Coleoptera (beetle) abundance was significantly related to breeding bird species richness, composition, and abundance, suggesting the possibility that beetle and spider communities may be important in structuring avifaunal communities. However, plant community composition was still the strongest predictor of breeding bird communities, and both bird species of concern showed marked preference for the vegetation found in fire-maintained longleaf pine savannas.