Evaluating Plant Diversity Effects in Native, Warm-Season Forage Mixtures.

Research suggests that a wide variety of ecosystem services are linked to plant biodiversity.  In May 2008, two field experiments were established in Blacksburg, VA to evaluate use of native, warm-season plants in forage-livestock systems.  A large-scale field experiment was established using three mixtures of native, warm-season plants with 1, 4 or 10 species.  Each mixture was planted in ~0.4 hectare plots with four replicates.  Species included in mixtures were five perennial grasses (e.g., switchgrass, indiangrass), three native legumes (e.g., Illinois bundleflower) and two broadleaf forbs (sunflowers).  The purpose of this experiment was to evaluate establishment dynamics and how defoliation management (biofuel or grazing) affected forage yield, nutritive value and weed biomass.  Using the same 10 species, a small-plot experiment was established concurrently with the large-scale experiment to evaluate how sown plant diversity affects ecosystem functioning.  Small plots were sown with randomly-assembled mixtures containing 1, 2, 4, 6, 10 species.  Yields from the first year of planting increased with increasing sown species richness in both the large and small plots.  More diverse treatments produced as much as 3.5 times more sown biomass than monocultures in the small-plot experiment and over 15 times more sown biomass in the large-plot experiment, while weed abundance was generally unaffected by sown species richness.  We will also present results from the second season describing yield and species composition data from these two experiments.  Initial results suggest that managing for higher plant diversity in these warm-season native mixtures can have positive effects in the year of establishment.