Productivity and Stability Relationships in Mowed Pasture Communities of Varying Species Composition

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Plant species composition of most managed pasture lands tends to be dominated by one or two species, usually a perennial grass and a legume. Recent ecological research suggests that increasing this forage diversity could increase pasture productivity and stability. We conducted a 4-yr field experiment to determine whether increasing the diversity of pasture mixtures would increase yields and improve interannual yield stability. Mixtures of cool-season pasture plants ranging from one to 15 species were planted into 2.25-m2 plots in May 1998. Interannual yield variation and yield responses to mowing frequency (2- vs. 4-wk frequency) were used to evaluate stability. Forage yields averaged <400 g m−2 yr−1 in mixtures having one or two species, while mixtures with three or more species averaged >1000 g m−2 yr−1 Increasing the diversity of mixtures beyond three sown species did not consistently improve yields. Interannual yield variation was lowest in the one- and two-species mixtures, and showed no consistent relationship with increasing species diversity. The number of species planted in each mixture declined by approximately 30% from 1999 to 2001, with the mixtures becoming dominated by perennial grasses. Although limitations in our experimental design prevent us from making strong conclusions about relationships between forage diversity and pasture productivity, our findings suggest that increased forage yield and stability may be best achieved by planting two or three forage species that are well matched to specific environmental conditions rather than planting a random assemblage of forage species in a complex mixture.