In recent decades, woody plants have been prolifically encroaching into grasslands in semiarid and subhumid regions. In the southern and central Great Plains, Juniperus virginiana is encroaching large areas of grassland and has been shown to reduce runoff by 20%-40%. Panicum virgatum, a native warm-season grass, has the potential to serve as a dedicated bioenergy crop but may increase or decrease runoff compared to native prairie. The goal of our research was to investigate how different land uses, and ecosystem conditions affect runoff in the southern Great Plains. In this study, we directly quantified runoff from a juniper-encroached watershed vs. runoff from watersheds that were cut and converted back to either native prairie or planted with Panicum virgatum in north-central Oklahoma. We used a paired watershed method and analysis of covariance to test changes in the runoff between the calibration and treatment periods for the experimental watersheds.
Results/Conclusions
We found that runoff from the restored native prairie and the planted Panicum virgatum watersheds both increased relative to their pre-treatment, juniper-encroached state. Cutting juniper and allowing recovery of native grassland vegetation increased runoff. Conversion of juniper to Panicum virgatum increased runoff substantially in the first year. These results indicate that that loss in water yield from woody plant encroachment can be restored by either allowing native prairie to reestablish or by planting a dedicated herbaceous biofuel crop.