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• Pulsed increase in sediment load follows mechanical removal of juniper. • Sediment load declines rapidly during the first growing season. • Converting juniper to grasslands increases water yield without sediment increase. Encroachment of woody plants into grasslands is a global phenomenon of environmental concern. Mechanical removal is often necessary to re-establish herbaceous dominance for heavily encroached watersheds, but its impact on water quality and quantity of runoff into streams and reservoirs has not been vigorously studied. The sediment concentration and load following mechanical removal of juniper (Juniperus virginiana , L.) woodland and subsequent re-establishment of tallgrass prairie or switchgrass (Panicum virgatum L.) biomass production were quantified at the experimental watershed scale in the south-central Great Plains, USA. Impact analysis was used to evaluate the effects of watershed treatment and phase of land use conversion. The annual sediment yield from juniper woodland watersheds averaged<0.10 t ha−1 yr−1 before treatment and increased to 0.28 t ha−1 yr−1 after juniper were cut and left on site. In the second year, removing the dried trees increased the annual sediment yield to 1.14 t ha−1 yr−1 in the prairie restoration watershed and 13.29 t ha−1 yr−1 in the switchgrass watershed that was sprayed with herbicide in preparation for no-till planting. The annual sediment loads averaged 0.44 t ha−1 yr−1 from the restored prairie and 0.29 t ha−1 yr−1 from the established switchgrass, comparable to 0.73 t ha−1 yr−1 from the intact juniper woodland during the third and fourth years after initiation of treatments. While restored grassland watersheds had elevated peak flows and longer flow duration leading to greater runoff, lower sediment yields were due to reduced mean and peak sediment concentration compared to the juniper watershed. Therefore, restoring juniper woodland to native prairie or switchgrass biomass production systems may increase water yield without increasing sediment yield, especially in years with extreme storm events. [ABSTRACT FROM AUTHOR]

• Paired watershed is effective in studying runoff response to woody encroachment. • Rooting zone soil moisture increased after converting juniper woodland to grassland. • Juniper removal in central Great Plains resulted in fivefold increase in runoff. Mechanical removal of encroached juniper (Juniperus spp.) is a common practice to restore native grasslands. However, the hydrological responses to grassland restoration remain mostly unquantified for the climate transition zone in the southern Great Plains of the USA where ecosystem evapotranspiration is highly sensitive to the change of vegetation functional type. We used a paired watershed approach to directly quantify the impact of mechanical removal of eastern redcedar (Juniperus virginiana L., redcedar) and restoration to native prairie or establishment of switchgrass (Panicum virgatum L.) on root zone soil moisture and event-based runoff for eight years including three main phases - calibration, transition, and restored grassland in north-central Oklahoma, USA. Results showed that the root zone soil water storage on average increased 1.6 and 1.9 times for restored prairie and switchgrass, respectively, after juniper removal. The regression model estimation based on the relationships established in the calibration phases between event-based runoff from control watershed and the treatment watersheds found that the restored prairie and switchgrass production system increased annual runoff by 4.46 and 4.54 times, respectively. These results indicated that both soil moisture and runoff are highly responsive to land use change in the southern Great Plains. Reestablishment of herbaceous dominance by mechanically removing encroached woody species is closely followed by restoration of soil moisture dynamics and watershed runoff regime. [ABSTRACT FROM AUTHOR]