Differential Species Response of Native Warm-Season Grasses to Defoliation Intensity in Pure Stands and Binary Mixtures.

To assess differential responses of native warm-season grasses [Andropogon gerardii Vitman (big bluestem), Tripsacum dactyloides L. (eastern gamagrass), Sorghastrum nutans L. (indiangrass) and Panicum virgatum L. (switchgrass)] to defoliation in pure and mixed binary-species stands, a field experiment was conducted at Virginia State University Research and Demonstration farm in Chesterfield County, near Ettrick, VA. For two consecutive years, strips (1.5 x 6 m) in the stands were harvested once, twice, or thrice a year at 20-cm stable-heights. In mid-June of the third year, three random second-year bunches of each species were separately clipped from the strips into paper-bags. For each bunch, the respective oven-dry (65 °C for 4 days) clipped biomass weight (g) was recorded. After the final harvest in late October, species crown diameters (cm) in respective strips for both stands were recorded. Data were analyzed as a Randomized Complete Block Design for effects of stand composition and harvest regimes on species performance. While pure stand biomass was greater for switchgrass than indiangrass, big bluestem, and gamagrass, in that order, their performances in the mixtures differed notably between harvest intensities. Switchgrass outperformed gamagrass and big bluestem in the one-cut strips, while the reverse was true in the three-cut ones. Gamagrass also remained vegetative longer than switchgrass, indiangrass and big bluestem. Data indicate that, in mixed stands, species contributions to stand biomass and potential changes in composition can be manipulated by intentional strategic defoliation management. Information on how fertility management might influence species response to defoliation in mixed stand is needed.