Browsing by Author "Zhangazha, Francis Tinashe"
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- ItemThe growth and knot property implications of a single stage thinning regime for Pinus patula saw log stands(Stellenbosch : Stellenbosch University, 2019-03) Zhangazha, Francis Tinashe; Du Toit, Ben; Wessels, Brand; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: The objective of the study was to analyse the growth and knot property implications of changing from the conventional two-stage thinning regime in Pinus patula saw log stands to a single stage mid-rotation thinning regime. (The investigation was done under conditions where no changes were made to the accompanying four-stage conventional pruning regime). The analysis of the growth ring widths showed that although individual trees in conventionally thinned stands, in both high and average site quality classes (hereafter SQ1 SQ3), yielded more individual mean DBH and more individual mean tree volume than conventionally pruned single thinned trees, single thinned stands yielded higher mean stand volume per hectare owing to a higher final stand density than the conventionally thinned stands. Single thinned stands on SQ1 have on average 26.1 m3 /ha greater mean stand volume than conventionally thinned stands of the same site quality class. The difference between conventionally thinned stands and single thinned stands in SQ3 was however not statistically significant. The mean knot diameter for the log unit ranging in length from 0 -7.2 m in conventionally thinned stands was on average either 0.36 cm (SQ1) or 0.30 cm (SQ3) larger than the mean knot diameter for the corresponding treatment in single thinned stands. Higher up the merchantable stem, the mean knot diameter for log unit of length range 7.2 -16.8 m in conventionally thinned stands was on average 0.27 cm larger than the corresponding value in conventionally thinned stands of SQ1. In SQ3, the difference in the mean knot diameter for log unit 7.2 -16.8 m in both treatments was not statistically significant. The merchantable stems of trees conventionally thinned have a higher share of sound knots (76 % for SQ1 and 74 % for SQ3) compared to that of merchantable stems of trees conventionally pruned single thinned (68 % for SQ1 and 69 % for SQ3, respectively). The study also contained two additional treatments where no thinning was carried out, either in the presence (P4T0) or in the absence (P0T0) of a conventional, four-stage pruning regime. In both site qualities, the pruning done in P4T0 led to an unexpectedly higher mean stand volume in P4T0 (194.2 m3 /ha for SQ1 and 95.8 m3 /ha for SQ3) compared to that of P0T0 (167.6 m3 /ha for SQ1 and 86.1 m3 /ha for SQ3, respectively). With a comparably higher percentage of sound knots, P4T0 also had a larger mean knot diameter compared to P0T0.