Impact of Eastern Redcedar (Juniperus virginiana L.) Canopy Diameter and Stand Canopy Cover on Aboveground Biomass and Composition in the Northern Great Plains Mixed-Grass Prairie

Eastern redcedar (ERC) (Juniperus virginiana L.) trees are invading prairies throughout the Great Plains. This encroachment poses a threat to native plant communities in terms of their production, regeneration, and diversity. The objectives of this study were to determine how ERC canopies impact herbaceous biomass production and composition. Square quadrats (0.25 m²) were placed in four cardinal directions underneath canopies of ERC trees ranging from 0.1–10 m in diameter and at grassland control locations. We collected herbaceous foliar cover by species and biomass estimates underneath 326 ERC trees and at 240 grassland control locations among two sites totaling 1381 samples overall. We found herbaceous biomass production underneath ERC canopies decreased exponentially with increasing ERC canopy diameter with 63–97% reduction under trees with canopies larger than 2 m. Also, biomass decreased linearly with increasing ERC stand canopy cover (%) at nearly a 1:1 ratio. Mean foliar cover for all species, Floristic Quality Index, species richness, and native species richness decreased as individual ERC canopy diameter increased. Results indicate that ERC encroachment is not only reducing herbaceous biomass production, but it is also altering the composition of plant communities. This highlights the importance of ERC control on grasslands and provides landowners with data that can be applied to their individual operation. To maintain or restore native grasslands, we suggest the removal of ERC through prescribed fire and/or mechanical removal every 5–10 years. Following these management strategies should maintain a healthy grassland system.