The Role of Allelopathic Interference in the Maintenance of Southern Appalachian Heath Balds

Gant, Robert

Allelopathic interference seems to be an important mechanism in the maintenance and persistence of southern Appalachian heath bald communities. Comparative analyses were conducted on two heath balds located in the Balsam Mountains of western North Carolina to distinguish phytotoxic characteristics that enhance persistence. Field studies revealed that one community was a mixed heath bald dominated by Rhododendron catawbiense and the second resembled an immature spruce-rhododendron forest heath dominated by Rhododendron maximum and Picea rubens. Caffeic acid, gallic acid, gentisic acid, hydroquinone, p-hydroxybenzoic acid, 2-pinene, phloroglucinol, rhododendrol, and vanillic acid were isolated and identified from canopy drip, leaves, litter, roots, and soil of the two heath balds. Bioassays run with aqueous leachates of heath bald litter and soil produced varying degrees of radicle reduction in three test species. Long-term inhibition by heath bald soils was confirmed in greenhouse experiments. Field studies demonstrated that environmental forces increased the allelopathic effectiveness of heath bald soils on seedling growth and survival. Influx of seed from the surrounding forests was sufficient to sustain invasion pressure against both heath balds. Allelopathic interference delays successional replacement of Rhododendron maximum heath balds by partially suppressing the establishment and growth of forest competitors. Heath balds dominated by Rhododendron maximum cannot maintain themselves and represent truly successional communities. Rhododendron catawbiense heath balds represent stable communities that employ allelopathic interference to arrest succession and maintain themselves. Communities of this type can be expected to persist in the southern Appalachian forests. Investigations of southern Appalachian heath balds revealed that these communities are more diverse and more involved in the succession of the regional vegetation than has been previously recognized.