Forest patch size, land use, and mesic forest herbs in the French Broad River Basin, North Carolina

The effect of forest fragmentation on cover-forest herbs was studied in the Southern Blue Ridge Province. Patches of mesic forest were sampled with 4 ha study plots. The coverage and density of herb species were greater in large patches (>200 h a) than in small patches (<10 ha). Several ant-dispersed species, such Disporum maculatum and Uvularia grandiflora, were more likely to be absent from small patches than from large patches. Wind-dispersed species, such as ferns and composites, were not affected by patch size and isolation. Small patches had reduced amounts of organic matter in the soil, suggesting that small patches have experienced more disturbance than large patches. Otherwise, there were not other differences in soil characteristics between patch sizes. Mechanisms hypothesized to have affected these populations include (a) disruption of population dynamics due to habitat fragmentation; (b) habitat degradation; and (c) anthropogenic disturbance via land use. Disturbances may have affected herb populations directly by increasing mortality rates and by degrading habitat. These habitat changes were confounded by the small size and isolation of smal forest patches.