Taper and volume equations for poplar trees growing on farmland in Sweden

Sammanfattning: Effective management of poplar plantations for high yield production would be facilitated by the availability of improved equations for predicting the taper and volume of poplar stems. Therefore, this thesis is based upon a polynomial stem taper equation and two volume equations constructed for individual poplar trees growing on farmland. Data for fitting and evaluate the taper and volume equations were collected from 51 trees growing in 27 stands in central and southern Sweden (lat. 55-60° N). The mean age of the stands was 22 years, mean density 970 stems ha⁻¹, and mean diameter at breast height 24 cm. Validation data were collected from 17 trees growing in ten stands, not used for fitting the equations. The outputs of the polynomial taper equation were compared with five published equations. The statistical evaluation indicated that the variable exponent taper equation presented by Kozak (1988) performed best and can be recommended. Because this equation´s complex construction, alternative recommendations were made. The constructed taper equation and the segmented equation presented by Max & Burkhart (1976) were second and third ranked. The first constructed stem volume equation is a function of diameter at breast height (DBH) and total height (H) as independent variables. In addition to these variables the other is also a function of an upper diameter. The outputs of these two equations were analyzed and compared to those of five published equations developed for, or applied on, poplar or aspen species. Of the stem volume equations examined the best performance was provided by the constructed equation with an additional upper diameter and recommended when precise and accurate volume estimations are required. However, because of difficulties to measure diameters high above ground, this equation is less practical in traditional surveys. For this purpose, the first constructed equation or the equation developed by Fowler & Hussain 1987 can be recommended. The taper and volume equations recommended in the study are likely to be useful in optimizing the efficiency and profitability of poplar plantation management.