During the week of 24 October, 1994, an international group of scientists mel in Uppsala, Sweden, to discuss the problems of understanding and modelling the growth of short rotation forests for energy purposes. Three working groups were formed to study specific aspects of the problem: ecophysiology, competition and modelling strategies. This special issue of Biomass and Bioenergy reports the findings of those groups and presents a series of papers related to the ecophysiology and process modelling of Salix. Copyright (C) 1996 Elsevier Science Ltd.