Variation in highway woody plant communities and soils along urban-rural gradients in Louisville, KY

 Linear vegetation patches are important landscape elements, promoting connectivity between urban and rural areas, providing barriers and filters for air and water pollutant movement, and serving as corridors for species movements. Species composition of the plant communities in these linear elements is an important determinant of their landscape functionality. Woody plant communities and soils were studied along three interstate highway corridors in Louisville, Kentucky. Woody plant communities along these interstates exhibited plant composition and soil differences that correlated with the abundance of the exotic shrub, Amur honeysuckle (Lonicera maackii). Communities dominated by honeysuckle had lower mean tree seedling and sapling density (27±0.8 100m^-2 with 33% exotic tree species) compared to plots dominated by native tree species (seedling/sapling density 271±72 100m^-2 with 0.31% exotic tree species). Woody plant species richness also differed, with native plant communities having nearly twice the diversity (18 species) of the honeysuckle communities (10 species). Soil characteristics also differed between communities dominated by honeysuckle versus native tree species. Honeysuckle plots had higher bulk density (1.104 vs 1.091 g cm^-3), soil pH (6.6 vs 5.7), and clay content (25.1% vs 19.5%) than low honeysuckle plots. These initial correlative studies suggest that shrub honeysuckle may be negatively affecting seedling regeneration of native woody tree communities in these highway forests and soil processes. In addition, the surprising existence of communities with valued native tree and shrub species provides optimism that native highway verge plant communities can be maintained even when edge-to-interior ratios and pollutant inputs are high.