Herbicides Have Variable Effects on Understory Plant and Insect Communities in Southern United States Working Forests

Working pine (Pinus spp.) forests in the southern United States rely on herbicides to remove competing vegetation and improve productivity. We conducted a review of the effects of herbicides on understory plants in southern working forests. We also discuss the impacts of herbicides on insect taxa associated with understory vegetation and its litter layer, including Coleoptera (carabid beetles), Hemiptera (true bugs), Hymenoptera (bees/ants), Lepidoptera (moths/butterflies), and Orthoptera (grasshoppers). Herbicides have few reported long-term impacts on understory herbaceous cover and species richness/diversity when applied according to labeled uses and application rates. However, the method of chemical treatment (e.g., broadcast spray or banded application) may influence understory plant structure and composition. Responses of insects to herbicides were species- and taxa-specific and highly variable given their forage/habitat requirements and life histories. Long-term research is needed to evaluate the effects of herbicides on vegetation-associated insects to provide a comprehensive profile of herbicide nontarget impacts. Study Implications: Land managers rely on herbicides to remove competing vegetation and increase working forest productivity. Given the objective of sustainable forest management to conserve biodiversity, it is important to understand how biological communities respond to chemical applications in intensively managed forest ecosystems. Our review indicated that herbicides have few reported long-term impacts on understory plant communities when applied appropriately. Despite their taxonomic diversity, invertebrates were rarely included in assessments of forest herbicides. Further research is needed to assess the potential nontarget impacts of herbicide applications on forest insect communities.