The growth and knot property implications of a single stage thinning regime for Pinus patula saw log stands

Zhangazha, Francis Tinashe (2019-03)

Thesis (MScFor)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die studie het ten doel gestel om die implikasies vir groei en houtkwaliteit te ondersoek wanneer die konvensionele twee-fase dunningsregime gewysig word na ʼn enkele midrotasie dunning in saaghout opstande beplant met Pinus patula. (Die ondersoek is gedoen onder toestande waar die gepaardgaande vier-fase snoeiregime onveranderd gelaat is vir beide die getoetsde dunningsbehandelings). Analise van die jaarring wydte wys dat individuele bome in die konvensionele regime, in beide hoë en gemiddelde boniteitsklasse (hierna BK1 en BK3) meer deursnee groei en volume produseer het as die behandelings met enkel dunning. Enkel gedunde opstande het egter meer volume per hektaar produseer as die konvensionele regime met twee dunnings, en dit word toegeskryf aan die groter stamtal in opstande behandel met ʼn enkel dunning regime. Konvensioneel gesnoeide opstande met enkel dunning op BK1 het gemiddeld 26.1 m3 /ha meer finale volume produseer as konvensioneel gedunde opstande van dieselfde klas. Dieselfde tendens het gegeld met opstande in BK3, maar hier was die effek nie statisties betekenisvol nie. Die gemiddelde kwasdeursnee op die stam seksie tussen 0 en 7.2 m hoogte in konvensioneel gedunde opstande was 0.36 cm (BK1) tot 0.30 cm (BK3) groter as die ooreenstemmende kwaste in die enkel dunning opstande. Vir die benutbare stam seksie van 7.2 tot 16.8 m hoogte was die kwaste in BK1 van konvensioneel gedunde opstande 0.27 cm groter as in die ooreenstemmende vakke onder ʼn enkel dunningsregime. In BK3 het die gemiddelde kwasgrootte op hoogte van 7.2 tot 16.8 m nie beduidend verskil tussen dunningsregimes nie. Die benutbare stamme van bome in konvensionele dunningsregimes het ’n groter fraksie van vaste, onbevlekte kwaste (76% vir BK1 en 74% vir BK3) vergeleke met ooreenstemmende behandelings in die enkel gedunde opstande (naamlik 68% vir BK1 en 69% in BK3). Die studie bevat ook twee behandelings waar geen dunning uitgevoer is nie, 'of in die afwesigheid of teenwoordigheid van 'n vier-fasige konvensionele snoeiprogram. In beide bonniteitsklasse het die snoeiprogram in gelei tot hoër gemiddelde opstandsvolume vergeleke met die ongesnoeide bome (die opstandsvolume in BK1 en BK3 was 194.2 en 95.8 m3 /ha vergeleke met 167,6 en 86.1 m3 / ha, onderskeidelik). Gesnoeide bome het 'n groter persentasie vleklose kwaste asook 'n groter gemiddelde kwasdeursneë as ongesnoeide bome gehad.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105666
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