LONG-TERM EFFECTS OF FoIxEST HEEWCIDES ON PLANT DIVERSITY IN PINE PLANTATIONS IN THE SOUTHEAST

Conservation of biological diversity is an important issue on public and private forests worldwide. As concern for diversity maintenance escalates, more pressure will be placed on the forestry community to understand the efjfects of silvicultural treatments on biodiversity and its sustainable management Biodiversity conservation in intensively managed forested regions will depend (at least partially) on species growing in tree plantations, their margins, SMZs, and rights-of-way. Within the-Southeast, pine plantation acreage is projected to double by 2040, mainly replacing natural pine forests. Replacemeut and establishment occur through intensive harvesting, using herbicides and mechanical treatments, burning, planting closely-spaced genetically-improved seedlings, and often fertilizing. The singular or additive effects of all these treatments lire often assumed to Iimit plant species riclxxss and diversity, yet little had been documcn?eci to support or refute that assumpiiox To learn more ahout di;tersit;l changes following herbicide treatments for site prepamtion and release, I have led two teams in conducting both a region-wide research project at 13 locations in. 7 states, and a study series in Central Georgia on 7 locations in 3 provinces. The following generalizations come tiom the tidings of these studies as well as fkom others’ related research. The Southeast is biologically rich with over 3,@00 species of plants. The richness and diversity of plants associated with pine plantations vary considerably across the region and its numerous physiographic provinces. A common flora does exist of species that range across the region. Non-native invasive plants are increasingly impacting this floristic diversity. Southeastern forests are naturally very resilient because they have developed through a long history of frequent burning, clearing, and harvesting. Most of the flora is composed of perennials that are capable of residing as underground parts, while both perennials and annuals persist in a rich soil seed bank. Plant species richness and diversity rebound rapidly after forestry herbicide treatments, with short and long-term compositional shifts according to the selectivity and effkacy of the herbicide(s) used. Total species richness and diversity are only temporarily reduced after treatment. In the long term (IO+ years) only perennial woody and semi-woody plants appear to be influenced, not total species richness. The density of the pine and/or hardwood canopy eventually dictates the composition, abundance, and spatial pattern of understory plants and their development. National Council for Air and S~reun Improvement, Inc. (NCASI). 2000. Proceedings of the 2000 NCASI Soufhern Regionaf Meefing. Resezcfi Triangle Perk, ?JC: National Couxi! for Air and Streur, Improvement Inc. National Council for Air and Stream lmprovemerll 2000 Southern Regicnal Meeting Proceedings 2 0 9