The influence of land use on forest structure, species composition, and soil conditions in headwater-slope wetlands of coastal Alabama, USA

Abstract

Wetlands are impacted by surrounding land use and land cover (LULC), but little information is available specifically on headwater wetlands. A total of 30 headwater wetlands were examined in coastal Alabama, USA, representing a range of surrounding LULC. Percent cover by forest, agriculture, and impervious surface area (ISA) (i.e., urban land use) were quantified in each corresponding watershed. Principal component analysis (PCA) was used to eliminate collinearity within land use data and produce orthogonal variables that represented gradients of forest cover, agriculture, and urban land use. Canopy tree density, diameter, species cover, importance values, and soil value/chroma were measured in each wetland. Exotic species cover was significantly related to land use change with increases in exotic shrubs associated with decreases in watershed forest cover. Field observations and analysis suggest that extensive colonization by the exotic shrub Ligustrum sinense may inhibit tree recruitment and alter wetland forest structure. Increases in shrub/sapling prevalence index (a measure of hydrophytic vegetation) and soil chroma were positively correlated to increased watershed conversion to agriculture (and concurrent loss of forest cover). Strategies for conserving the services associated with these wetlands should include minimizing surrounding forest loss and maintaining groundwater inflow.