1. Faculty of Life and Health Sciences, School of Environmental Sciences; University of Ulster, Cromore Road; Coleraine BT52 1SA U.K.
2. Centre for Forestry and Climate Change; Forest Research, Alice Holt Lodge; Farnham GU10 4LH U.K.
3. Centre for Forest Resources and Management; Forest Research, Northern Research Station; Midlothian EH25 9SY U.K.