Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2003
Publication Date: 6/30/2004
Citation: Sanderson, M.A., Skinner, R.H., Barker, D.J., Edwards, G.R., Tracy, B.F., Wedin, D.A. 2004. Plant species diversity and management of temperate forage and grazing lands. Crop Science. 44(4):1132-1144 Interpretive Summary: Recent ecological research indicates that increased plant species diversity increases primary production in grasslands and benefits other ecosystem functions as well. It is not clear, however, how these results and concepts relate to managed grasslands. Certainly, the potential benefits of biodiversity, such as increased productivity, greater stability of production, and enhanced nutrient cycling, are highly relevant to forage and grazing land management. The limited research data point to benefits of using species-rich mixtures in pastures. Including species from a broader range of functional groups (e.g., broadleaf forbs in addition to grasses and legumes) and targeting species-rich mixtures to environments with highly variable soils, weather, and management are two recommendations supported by the data. More data are needed from grazing trials that measure animal productivity on a range of species mixtures at relevant scales so that practical recommendations can be made for grazing management. Systems research is needed on using diversity at the farm scale where combinations of simple mixtures or monocultures are used in several fields instead of focusing on complex intimate mixtures. Finally, embracing a multi-functional view of grazing lands to include environmental benefits as well as productivity opens the door for greater use of biodiversity in sustainable grazing land management.
Technical Abstract: Postulated benefits of increased species diversity in grasslands include increased primary production, greater stability of production, and more efficient use of nutrients. These benefits have been extrapolated to forage and grazing land systems with little supporting objective data. We explore this debate and discuss the potential application of biodiversity concepts to the management of temperate forage and grazing lands. Plant species diversity refers to the number of species (species richness) and their relative abundance (species evenness) in a defined area. Plant relations influence biodiversity responses through positive interactions (e.g., facilitation, N2 fixation, hydraulic lift) or competitive effects (e.g., competitive exclusion, allelopathy). Grazing animals alter plant diversity through direct effects of biomass removal, altered competitive interactions, deposition of nutrients, and the creation of sward gaps. Most information on the potential benefits of increased plant diversity comes from studies of synthesized grasslands that have not included domestic grazing animals. Early 20th century research on complex mixtures of forage species (limited to grasses and legumes) for pasture indicated equivocal results regarding benefits of species-rich mixtures and typically recommended using the best adapted species in simple grass-legume mixtures. Recent research from the USA, UK, and New Zealand indicate herbage yield benefits from species-rich mixtures for pastures. In the only animal productivity grazing trial with species-rich mixtures, milk yield per cow (35.6 kg d-1) and grazed dry matter intake (13.7 kg d-1) did not differ on pastures of two to nine species. Herbage yield, however, was 50% greater in the species-rich pastures indicating a greater animal productivity per ha. Grazing land productivity is a primary focus for biodiversity benefits because of the direct economic relevance to producers. Taking a broader view of the multi-functionality of grazing lands to include environmental and aesthetic benefits to humans reveals a great scope for using biodiversity in grazing land management. Sustainable use of grazing lands depends on maximizing their functionality.