Investigation of tree height estimation accuracy during 1998-2010 NFI of Lithuania

Abstract

Accuracy of mean tree height estimations per plot changes from 3-5 % in stands with mean diameter of 40 cm and more, up to 5-20 % in stands with mean diameter of 4-20 cm. Mean deviations of modeled heights from measured for trees of all population of prevailing and admixture species do not exceed ± 1-3 cm. Differences between modeled and measured tree heights for stands with mean diameter 4 (2.1)-44 cm statistically are not reliable. Two tree species groups with different character of height deviations, for trees with diameter lower or larger than mean diameter of stand were divided. Systematical deviations up to 9-28 (33) cm were estimated for modeled heights of trees with diameter up to and over the mean diameter in pine, (oak), birch and black alder stands while in spruce, aspen, grey alder and ash stands such deviations had random character, not exceeding 6 (9) cm. In general positively evaluating all the system, used for tree height estimations during NFI, some improvements for tree species of the first group could be done by correcting generalized height- diameter model. Height estimation of every tree, measured on NFI sample plots is based on diameter- height measurements of small size sample trees. Height is measured for every seventh tree on sample plot (Kuliešis et.all, 2003, 2009). Heights and diameters of 3-5 trees of prevailing and 1-3 trees of other, admixture species, are measured in average per plot. Heights of the rest trees are estimated using generalized height- diameter model (Kuliešis, 1993) and data of measured diameters of all trees as well as height-diameter of sample trees. The goal of this study is to estimate accuracy of tree height estimations, using generalized height- diameter model and height-diameter measurements of small size sample trees. Data for this study were used from diameter-height measurements of 47.5 thousands sample trees of prevailing eight tree species – pine, spruce, birch, aspen, black alder, grey alder, oak, ash and 24.6 thousands sample trees of the same tree species, as admixture in stands, on 1998-2010 NFI plots. Deviations of modeled heights from measured and their significance were estimated depending on tree species, tree position - prevailing or admixture, mean diameter and mean height of the trees for all trees and separately for thinner and thicker to compare with the mean stand diameter of trees. The heights of the trees in spruce and oak stands are characterized by the most and in black alder and aspen stands – by the least variation per cell with the range of mean diameter ± 2 cm and range of mean height ± 1 m.