CUMULATIVE MERCHANTABLE STEM VOLUME EQUATIONS FOR POPLAR (POPULUS. SPP.) PLANTATIONS ON FARMLAND IN SWEDEN
03 - Bioenergy: Economy, Market and Policy
1 BIRGER HJELM, 2 THEO VERWIJST
1 DEPT. OF CROP PRODUCTION ECOLOGY - SWEDISH UNIVERSITY OF AGRICULTURAL SCIENCE
2 DEPT. OF CROP PRODUCTION-SWEDISH UNIVERSITY OF AGRICULTURAL SCIENCE
In Sweden there is an increasing interest in the use of poplar, mainly as a future bioenergy supplier. Effective management of poplar plantations for high yield production would be facilitated by equations providing better predictions of commercial stem volume than currently available equations. Two equations were developed for estimation of commercial stem volume for poplar trees (Populus. Spp.) The commercial stem volume can, with these equations, be estimated for either any given top diameter or any bole length, in contrast to traditional volume equations that give one estimate, only, for the whole tree. The independent variables used in the equations are diameter at breast height (DBH), total stem height (H) for both equations and given top diameter (d), for (Eq. 1) and given bole length (h) for (Eq. 2). Data for fitting the equations were collected from 107 poplar trees growing at 39 stands in central and southern Sweden (lat. 55–60° N). The mean age of the stands was 17 years (range 7–30), the mean density 980 stems·ha−1 (190–3 404), and the mean diameter at breast height (outside bark) 24.2 cm (range 12.1–40.8). The stands were growing on former farmland and all stands were located on sites with clay sediments, with textures ranging from light to medium clay. The management of the stands varied; some had not been thinned at all, while the others had been moderate to heavy thinned.To verify the tested equations, performance of accuracy and precision in the cumulative stem volume predictions at five points along the stem were closely analysed, as well as an overall performance for the whole tree. Statistics used for evaluation of the equations show that the commercial volume equation based on any given top diameter (Eq. 1) performed better than the equation based on any given bole length (Eq. 2) with R2 of 0.992 and 0.990 respectively, Absolute Bias 0.046 and 0.051 (m3) respectively and Root Mean Square Error (RMSE) of 0.0663 and 0.0717 respectively. The commercial stem volume equations developed in the study is likely to be beneficial for optimising the efficiency and profitability of poplar plantation management when having trees with larger diameters within the plantations that can be harvested for additional timber assortments other than bioenergy.
Keywords: forest management; forest production; commercial volume equations; bioenergy
Acknowledgments: This work acknowledges all the people that has carried out the time consuming and hard work to collect the field data for this study, especially to mention is Mr Jonas Johansson and Mr Lars Hedman.
