Submitted to: Basic and Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2009
Publication Date: 4/29/2010
Citation: Sanderson, M.A. 2010. Stability of production and plant species diversity in managed grasslands. Basic and Applied Ecology. 11(3):216-224.
Interpretive Summary: Complex mixtures of many forage grasses and legumes in pastures have been viewed as being more stable in terms of forage yield with time and more efficient in the use of environmental resources than monocultures or simple mixtures. A retrospective analysis was conducted of three studies in which 181 mixtures of forages were compared for several years. The objective was to determine the relationship between the number of species sown in mixtures and the resulting herbage yield along with an examination of whether increasing mixture complexity contributed to yield stability with time. The analysis of forage yield variability in 181 mixtures of temperate grasses and legumes revealed that monocultures and two-species mixtures had lower yield stability year to year than more complex mixtures. Within forage mixtures, however, there was no consistent relationship between forage yield or yield stability and measures of plant species diversity or mixture complexity. Results of this research revealed that forage species identity and composition of forage mixtures may be more important determinants of herbage yield than simply the number of species included in a mixture.
Technical Abstract: Plant biodiversity theory suggests that increased plant species diversity contributes to the stability of ecosystems. In managed grasslands, such as pastures, greater stability of herbage production would be beneficial. In this retrospective study, I used data from three reports from the 1930s, 1940s, and 1960s to determine whether increasing mixture complexity contributed to yield stability with time. Yield data from a total of 181 mixtures of grasses and legumes (two to seven species per mixture) in experiments of 3 to 6 yr duration in Connecticut, Pennsylvania, and Utah, USA were used in the analysis. Regression was used to examine relationships among herbage yield, stability of yield [measured as the interannual coefficient of variation (CV)], and diversity measures [Shannon diversity index (H), species richness (S), and evenness, (J)]. In several instances there was no relationship between herbage yield or yield stability and the complexity (number of species) of the mixture. In one experiment, the proportion of legume in the sward seemed to be the controlling factor regarding herbage yield and yield stability. Monocultures and binary mixtures frequently had the highest interannual CV (e.g., less yield stability) than more complex mixtures. Within forage mixtures, however, there was no consistent relationship between herbage yield or yield stability and measures of species diversity. Species identity and composition of forage mixtures may be more important determinants of herbage yield than simply the number of species.