Approaches for sustainable management of Cupressus lusitanica stands on Jabel Marra [Sudan]

The present study involved assessment of the Cupressus lusitanica plantation area/structure, stands diameter distribution and suitability the management option adopted. The results indicated that the present state of C. lusitanica stands can best be managed on selection harvesting system to sustain sawn timber and building poles production. The selection system enhances natural regeneration. The inverted J-shaped diameter distribution constituted the basis for selection system where selected target trees are replaced, with time, by development of trees from the series of DBH classes. Comparisons of various sampling procedures were carried out using the 100 enumeration as a control. A 20-acre, 38-year old, C. lusitanica stand at Beldong Forest, Jebel Mara, was selected for the present study. Systematic and random sampling were used for estimation of basal area based on 10 sampling and 20 circular sample plots. Systematic arrangements of 10 concentric circles were included in the study using circles with 11.3m, 15.6m and 17.8m radii. Strip sampling with 10 intensity, using two strips of one acre area each, was done. In addition, two subjective methods were employed using a sample plot to represent average stocking and two sample plots to represent the maximum and minimum stockings. The DBH obtained by the 100 enumeration for each numbered tree was entered in the computer and used as the basic data for all the sampling methods. For each sample plot located in the field in connection with any of the sampling procedures, the trees were recorded by their numbers to facilitate collection of their DBH in the basic data. One year later, 10 concentric circles with 11.3m, 15.6m, and 17.8m radii were randomly distributed. DBH of the tree were measured. The circles centers were used for basal area counts using a Spiegel Relascope. Average basal area per acre was calculated for the 100 enumeration and for each of the sampling procedures using personal computer. Comparison was carried out between the average basal area per hectare for the 100 and each of the systematic and random sampling procedures and the first 10 concentric circles using the equation Z = X-M /S/n strip sampling and subjective methods were compared on the basis of logic since their sample size were not enough to facilitate a statistical comparison. Duncan multiple range test was applied for significance test for the second group of concentric circles with the relascope methods. Results indicate that the systematic sampling basal area estimates are not significantly different from that obtained by the 100 enumeration but the random sampling and strip sampling are significantly different. The subjective method accuracy depends on experience, and in the present study its results are not significantly different from the 100. The relascope and the concentric circles estimates are not significantly different.