Joe J Landsberg1, Richard H Waring2, Mathew Williams3. 1. `Withycombe' Church Lane, Mt Wilson, NSW 2786, Australia. 2. College of Forestry, Oregon State University, Corvallis, OR 97330, USA. 3. Centre for Sustainable Forests and Landscapes, School of GeoSciences, NCEO, The University of Edinburgh, Edinburgh EH9 3FF, UK.