A compatible tree volume and taper estimation system for juniperus procera hocht. ex endl.: grown at Menagesha Suba State Forest, Central Ethiopia

A volume-based compatible volume and taper estimation system has been developed for Juniperus procera growing at Menagesha Suba State Forest. The system is based on compatible polynomial taper equation derived around standard logarithmic volume equation which was selected as "best" volume equation among four most well known volume equations. Given diameter at breast height and a measure of height, then total tree volume, volume to any height or upper stem diameter and upper diameter at a given height on the main stem can be estimated by the system. Stem analysis data from 229 standing trees measured in natural stands and plantations of Juniperus procera were used to compare the volume functions for ability to predict most accurately and precisely total tree volume. The four volume equations compared were: constant form factor, unweighted and weighted combined variable, Schumacher's logarithmic and Honer's transformed equations. The equations were evaluated on the basis of a number of fit and validation statistics and graphical examinations of the residuals. Results indicate that Schumacher and Hall's logarithmic total volume equation outperformed all other volume equations. Honer's equation ranked behind the logarithmic equation, followed by weighted and unweighted combined variable equation. The constant form factor clearly looked poorer than the rest. Goulding and Murray's a fifth-order compatible polynomial taper equation was constructed around logarithmic total volume equation for estimating total and partial volume and stem taper. Various measures of accuracy and precision were calculated for individual stems using the observed and predicated diameters and volumes at each 10 percent height along the stem, from ground to top. For natural stands independent data set, individual diameter estimation has a bias of minus 0.01 cm and a standard deviation of differences (Sp) of 4.02 cm and volume estimation has a bias of 0.03 m cubic and Sp of 0.468 m cubic. For plantations independent data set, diameter estimate has a bias of 0.39 cm and SD of 1.81 cm and volume estimation has a bias of minus 0.004 m cubic and SD of 0.055 m cubic. These biases and standard deviation of differences indicate a good fit based on comparison with published results of the same equation. The system developed in this study conforms with most of the desirable properties of volume and taper equations, although it shows a slight tendency to produce greater bias in diameter estimation above 80 percent of the total height. This system shows a substantial improvement over existing volume estimation system in Ethiopia, as it avoids inconsistent volume estimates produced for different section volumes of a single tree by different volume equations. It is recommended that higher power term be included to improve the accuracy of the equation and that separate volume and taper equation be constructed for each growth type stand when the system is required for experimental trials.