Affiliation: | Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK;;Springhill Farm, Standen Street, Benenden, Cranbrook, Kent TN17 4LA, UK;and;Centre for Ecology and Hydrology, Dorset, Winfrith Technology Centre, Dorchester, Dorset BH20 5AS, UK |