1. WWF-UK, Panda House, Weyside Park, Godalming, Surrey GU7 1XR, UK
2. School of Geography and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
3. Ecological Processes and Management, NERC Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, UK