Grasslands, grazing and biodiversity: editors' introduction.
This paper serves as an introduction to a special journal section on grazing and biodiversity in grasslands. Natural, semi-natural and artificial grasslands occur extensively around the globe, but successful management for production and biodiversity poses several dilemmas for conservationists and farmland managers. Deriving from three continents (Africa, Australia and Europe), papers in this Special Profile interface three specific issues: plant responses to grazing, plant invasions and the responses to management of valued grassland biota. Although pivotal in grassland management, plant responses to grazing are sometimes difficult to predict. Two alternative approaches are presented here. The first uses natural variations in sheep grazing around a water hole to model the dynamic population response of a chenopod shrub. The second analyses a long-term grazing experiment to investigate the links between plant traits and grazing response. Linked often crucially with grazing, but also driven sometimes by extrinsic factors, invasions are often cause for concern in grassland management. The invasions of grasslands by woody plants threatens grassland habitats while the invasions of pastures by alien weeds reduces pasture productivity. The papers in this section highlight how a complementary range of management activities can reduce the abundance of invaders. A final paper highlights how global environmental change is presenting new circumstances in which grassland invasion can occur. The impact of grassland management on biodiversity is explored in this Special Profile with specific reference to invertebrates, increasingly recognized both for the intrinsic conservation value of many groups and for their role in ecosystem processes. The potential for manipulating flooding in wet grasslands to increase the soil invertebrate prey of wading birds is illustrated, together with the roles of management and landscape structure in enhancing insect diversity. In the face of climate change and growing demands for agricultural productivity, future pressures on grassland ecosystems will intensify. In this system in which productivity and conservation are so closely bound, there is a need both to raise the profile of the issues involved, and to improve our understanding of the applied ecology required for successful management.