Herbaceous species composition and richness of mesophytic cove forests in the southern Appalachians: synthesis and knowledge gaps
We synthesized the current information on mesophytic cove forests in the southern Appalachians, assessed the range of variation in herb species composition and diversity in stands with different disturbance histories and environmental conditions, identified key knowledge gaps, and suggested approaches to fill these knowledge gaps. The purpose of this synthesis was to provide information to forest managers to help make decisions about conservation assessments and strategies for rich cove forests in the southern Appalachians. An important finding is that no single study or data set can provide conclusive evidence or clear management strategies. However, an overriding conclusion is that the magnitude of impact and the management actions necessary to restore herbaceous communities are directly proportional to the severity of disturbance, current condition (e.g., presence of Rhododendron), site heterogeneity, and historical land use (e.g., agricultural activity). These factors plus a host of other stressors (e.g., climate variability, air pollution, invasives) are likely to have a strong influence on the highly variable patterns observed when comparing herbaceous diversity of ‘old-growth’ or uncut forests to human disturbed forests (e.g., cutting, air pollution, conversion, invasive plants or insects). Results from this review reinforce our premise that factors controlling herbaceous species presence and abundance are highly complex, thus broad generalizations about the impacts of a single factor such as logging should be interpreted with caution. Of the stressors known to affect forest trees (e.g., pests and pathogens, acidic deposition, air pollution, drought, and wind), little to no information exists on how these same stressors will affect herbaceous plants. A limited number of studies have examined the demography or physiology of forest herbs, particularly across all life stages. While the demography of a few genera have been studied (e.g., Hexastylis, Asarum, Trillium, Arisaema, Goodyera, Hepatica), little to no information exists for the majority of woodland herbs. Species identity is important when considering management of rich cove forests. Diversity may increase following canopy disturbances that favor recruitment of early-seral herbaceous species; therefore, simple indices of diversity (H', S, and E) are not the best measure of recovery in mesophytic rich coves, particularly where shade-adapted ‘rich-cove indicator’ species have been replaced by these species. Species-specific life histories and the influence of prevailing site conditions are important lines of research for understanding recovery and sustainability of mesophytic rich cove forests.