Temperature restraints on energy forestry in Sweden

Temperature sums (TSUM) and growth units (GU) were used as driving variables in the modelling of energy forest production in Sweden. To construct regional maps of forest production for years with good, average and poor weather conditions, it was necessary to deduce formulae of TSUM and GU on a regional basis for a growing season, defined by daily mean temperatures exceeding 5 ÐC. Temperatures north of the 900 day-degrees line are too low for intensive growing of energy forests of willow clones studied so far. With an average production of 10 tonnes dry matter per hectare per year on one million hectares, available for energy farming in the remaining part of Sweden, energy forests could replace about 20% of the Swedish oil import.