Trends and productivity improvements from commercial willow plantations in Sweden during the period 1986–2000

The production trends of commercial willow plantations for bioenergy in Southern and Central Sweden were studied for the period 1986–2000 based on harvest records of the first cutting cycle after the establishment of 1512 plantations. The trends were modelled by using a mixed model in order to include the variability of management options by the growers, which were grouped into four classes according to their performance. The spatial variability of the productivity is included using an agro-climatic index based on the official estimates of oat yields. Results of the study show average yield increments of 2.06 odt ha−1 yr−1 per decade. Areas with high productivity have significantly increased the yields of willow during the period studied, from 1.3 to 5.4 odt ha−1 yr−1. Regarding management, the best growers group shows a national average increment of 2.75 odt ha−1 yr−1 per decade, and the latest plantings reach an average of 6 odt ha−1 yr−1. This group is formed by farmers with previous experience growing willow, who tend to have significantly higher yields. In addition, experienced farmers increased their yields an average of 0.34 odt ha−1 yr−1 regardless of the group they were classified in. It is expected that future improvements of the willow varieties will result in a significant increase in the mean yields in the near future.