Development of Volume Estimating Systems for Cupressus lusitanica on Jebel Marra

Abstract

The study was carried out on Cupressus lusitanica at Beldong Forest Reserve, jebel Marra area, Western Sudan. The main objectives of the study included: -Development of height-diameter relationship. -Comparison between Newton's, Smalian's and Huber's formula as used for log volume estimation. -Construction of tree volume tables for three top diameter limits, up to top, up to 7.0 cm and 10.0 cm top diameters. -Development of taper function, relating upper stem diameter to measurable parameters, including diameter and height. A total of 2800 trees were randomly selected from all over the forest and their diameters at breast height and total heights were measured and used to construct height-diameter equation. For the volume table construction a total of 187 trees were randomly selected from the 2800 trees covering all the diameter classes. The selected trees were felled and sectioned into two meters logs. Large end diameter, mid-diameter and small end diameter were measured for every log in cm to the nearest decimal. Sections volumes were calculated using Newton's formula: The total volume, volume to 7.0 cm top diameter and volume to 10.0 cm top diameter were obtained for every felled tree by summation of sections volumes of each tree. Four volume models were tried using regression analysis. The first model was the combined variable model The other three models were produced by adding (d2) and (h) to the combined model respectively. These volume models have been tried for the three utilization levels. The results showed that, the combined variable model resulted in the best fit for all the utilization levels. The addition of (d2) and (h) to the combined variable model, did not develop any significant improvement in explaining volume variability. Tree volume tables for the three utilization levels have been produced for C. lusitanica for Jebel Marra conditions on the basis of diameter at breast height and total height of tree. For the study of taper function for C.lusitanica, the data were collected from the felled trees, where upper diameters were taken at intervals of one meter. Taper functions were developed. Taper models produced will enable the user to determine diameter at a given height, or height at a given diameter for any utilization standards. Comparison of volume formulae (Newton's, Huber's and Smalian's) using different log length of 2, 4 and 6 meters, has been made. No significant differences were found between the three formulae. Huber's formula results in estimates closer to Newton's than Smalian's does. Smalian's formula overestimates the volume while Hubers formula underestimates the volume using Newton's as a control. The error –due Huber's application is consistently half that produced by Smalian's.