Development of Volume Estimating System for Cupressus lusitanica Plantation on Jebel Marra, Sudan

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Date
2004
Authors
Elsiddig, E.A.
Idris, E. A.
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Faculty of Agriculture, University of Khartoum, Shambat, Sudan
Abstract
For log volume computation and tree volume equations construction, 187 trees from Cupressus lusitanica plantation were randomly selected, covering the range of diameter at breast height classes (dbh) from 7.0 cm to 38.0 cm. The selected trees were felled and sectioned into 2.0, 4.0 and 6.0 metres logs. Large end diameter, mid-diameter and small end diameter were measured in cm for every log. Section volumes were calculated, using Newton's, Huber's and Smalian's formulae. Comparison between Huber's and Smalian's equations was made using Duncan's multiple range test and Newton's as control. No significant differences were found between the three equations. When applied to the pooled log population within each log class, Huber's formula resulted in log volume estimates closer to Newton's than Smalian's did. The error due to application of Smalian's formula was consistently higher than that produced by Huber's formula but not significantly different, and the latter was more accurate than the former and required less measurements and computation. Regression technique was adopted for the derivation of tree volume equations for C. lusitanica plantation for total volume, volume up to 7.0 cm and up to 10.0 cm top diameter utilization limits, using the 187 sample trees. During the fitting process of the regression model to the data, the combined variable equation v = b0+ b1d2h constituted the starting formula to which d2, h or both were added in step-wise process. The combined variable equation resulted in the best fit for all the utilization levels. The addition of d2 or h did not result in any significant change in the combined variable equation as indicated by R2. The equations of best fit were selected for the three utilization levels for C. lusitanica in Jebel Marra conditions.
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Page(s):12 (2), 235-248, 24 Ref.
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