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Conference abstract, 2010

Comparison of three models for estimation of poplars stem taper

Hjelm, Birger; Johansson, Tord


In Sweden, poplar has until now only been planted on small areas. The plantations have been established mainly in 1980-1990 when some of the farmland areas were laid down. Most of the planted areas have been arranged for exposing the capacity of the specie. Today there are about 300 hectares of poplar plantations in Sweden. The plantations are dominated by the clone OP 42 (P. maximowiczii x P. trichocarpa). Due to high and increasing demand for biofuel in Sweden, the interest for poplar as suitable short rotation specie has increased. However, equations for prediction of volume for individual poplar, taper equations and yield tables for poplar stands for Swedish conditions are missing. In a newly started project dealing with poplar as promising specie for future production of biomass, mainly for pulpwood and bio fuel, the present study is one important part. Construction of tables and equations is of great importance as base for presenting practical recommendations aiming an efficient forest management for high biomass production combined with an economical outcome. The objective of the study was to develop a taper model easy to use, not segmented, yet applicable for all stem sections, predicting diameter at a given height or a height at a given diameter. Field data were collected from 33 stands where 68 trees in total were sampled. The stands were localized on three areas in central and southern Sweden (Lat. 55-60˚ N.). Most of the stands have not been managed properly. As damages by wild games are intense in Sweden, fencing the plantation is an important way to decrease the damages. The stands have not been thinned in time, which cause strong competition and in some cases self thinning. The sampled trees were felled and diameters, tree heights and crown heights were measured. The total age and age of different segments of the stem was defined through annual ring counting. Stem number per hectare ranged between 155 and 3493, tree age between 14 and 73 years, tree height between 10 and 32 m and the stem diameter at breast height between 124 and 512 mm. The output of a four degree polynomial taper equation (Hjelm 2010) was compared and analyzed with two published equations (Kozak et al 1969, Benbrahim & Gavaland 2003) for predicting stem form. The results show that Kozaks quadratic equation had less adaptation for predicting diameter in the lowest neiloid shaped stem section than the other equations. The polynomial equation in the study showed a significantly better adaptation along the main stem with parabolic form than the other equations. The correlation was high for all three equations with R2 = 0.99 for Kozaks and Benbrahim & Gavalands equations respectively and R2 = 0.98 for the polynomial equation. The root mean square error (Rmse) was 0.0718 for Kozaks equation and 0.0601 for Benbrahim & Gavalands equations and 0.0494 for the constructed polynomial equation. Data from the present study will be used in a later study on stem volume and yield tables for poplar. Taper equations and form factors from the present study will be important inputs for the construction of the volume equations. The forest owner will then have a tool for estimating the future yield of poplar plantations on former farmland

Published in

Book title: Fifth International Poplar Symposium : poplars and willows: from research models to multipurpose trees for a bio-based society : 0 – 25 September 2010 Palazzo dei Congressi Orvieto (Italy) : book of abstracts
Publisher: IUFRO


Fifth International Poplar Symposium

Authors' information

Hjelm, Birger
Swedish University of Agricultural Sciences, Department of Energy and Technology
Johansson, Tord
Swedish University of Agricultural Sciences, Department of Energy and Technology

UKÄ Subject classification

Renewable Bioenergy Research
Forest Science

URI (permanent link to this page)