Eastern redcedar (Juniperus virginiana, ERC) is encroaching tallgrass prairie ecosystems in the southern Great Plains which increases aboveground biomass and reduces water runoff. These lands could be converted to switchgrass (Panicum virgatum) or restored to native prairie. Our objective was to determine the water use efficiency (WUE) of ERC, switchgrass and native tallgrass prairie. We hypothesized that 1) ERC would have greater aboveground net primary productivity (ANPP) than switchgrass or native prairie and 2) WUE will be similar among ecosystems because the greater ANPP of ERC will be balanced by greater evapotranspiration (ET). Data were collected in northcentral Oklahoma on six experimental watersheds, four of which were initially ERC and two of which were native prairie. ERC was cut from two watersheds and removed. One watershed was allowed to reestablish as native prairie and the other was planted as switchgrass. Tree aboveground biomass was determined annual diameter measurement and allometric equations. Herbaceous biomass was determined using clop plots sampled towards the end of each growing season. Runoff was measured using H-flumes. Annual ET was estimated as the difference between precipitation and runoff. Annual WUE was calculated as the ratio between ANPP and annual ET.
Results/Conclusions
In 2018, ANPP of the switchgrass growing on the cut ERC watershed (10.05 Mg ha-1) was significantly greater than for the other watersheds. The ANPP of the switchgrass growing on the converted prairie (7.12 Mg ha-1) greater than one of the ERC watersheds (3.21 Mg ha-1) and the native prairie watershed (4.92 Mg ha-1). Runoff was greater from the switchgrass watersheds and least from the ERC watersheds meaning less water flowing to streams with ERC encroachment. ET was greatest on ERC watersheds, with up to 99% of precipitation being lost to ET in certain years. WUE(s) of switchgrass watersheds were greater than those of native prairie and ERC watersheds indicating more biomass production per unit of water use. Therefore, restoring ERC encroached watersheds to native grassland or switchgrass systems can increase water yield, ANPP and WUE which have positive environmental and economic benefits.