Higher initial planting densities for South African-grown Pinus patula sawlog trees: the effect on stem form and land expectation value

Thesis (MScFor)--Stellenbosch University, 2018.ENGLISH ABSTRACT: There are concerns that the modulus of elasticity (MOE) of Pinus patula lumber in South Africa has decreased mainly due to faster growth and reduced rotation ages. However, a number of recent studies have shown that increased planting densities can improve mean stiffness of wood from several softwood species. Additionally, stem form could possibly also improve with higher planting densities. The objectives of this study were to evaluate the effect of Pinus patula saw log management regimes, based on higher initial planting densities, on land expectation value (LEV) and stem form. Stem form has a large influence on volume and value recovery in sawmills and the influence of stem form characteristics can be considered when calculating log values using software programmes such as Simsaw. This study was conducted using an 18 year-old Pinus patula experimental spacing trial. The trial was located near Barberton on the Mpumalanga escarpment. The experiment consisted of two replications of four planting densities (403, 1 097, 1 808, and 2 981 spha). Stem form characteristics (ovality, straightness, sinuosity, butt-flare, and taper) from each spacing treatment were assessed from Lidar scanning data. The trial was felled and logs processed into structural size lumber which were destructively tested for MOE and modulus of rupture (MOR). The board MOE, together with sawing simulation results, were used to assign a log value recovery to each log class from each spacing treatment. Together with South African forestry cost data, the land expectation value for a range of planting density treatments and thinning regimes were calculated. Spacing treatment had a significant effect on all five stem form characteristics. Over the bottom nine meters of the stem, the lower spacing treatments (403 and 1 097 spha) had mean stem deviations of 132.1 mm and 109.3 mm respectively while the higher planting densities (1 808 and 2 981 spha) had mean stem deviations of 76.4 mm and 82.1 mm respectively. Taper and butt-flare also had a decreasing trend from 403 spha to 2 981 spha. Ovality, on the other hand, increased with increasing planting density and also increased with increasing height along the tree stem. There was an increase in mean MOE of lumber with increasing planting density. Similarly, the structural grade recoveries of similar board positions increased with planting density. This, in turn, resulted in increased log value recovery, for the same log sizes, with increased planting density. The best management regimes for each of the three lower planting densities (403, 1 097, and 1 808 spha) all returned LEV values relatively close to each other. The best LEV was from a spacing treatment of 1 808 spha, thinned at 12 years to 300 spha, and clearfelled at 19 years (R47 693.02/ha. The second best management regime was for the 1 097 spha planting density, thinned to 250 spha at 13 years, and clearfelled at 18 years (R46 677.59/ha). Despite the results showing that higher planting densities result in better value recoveries for the same log sizes, the best LEV was not obtained from the highest planting density but with a medium high planting density and a late thinning.AFRIKAANSE OPSOMMING: Daar is kommer dat die modulus van elastisiteit (MOE) van Pinus patula hout in Suid-Afrika afneem weens vinniger groeikoerse en laer rotasie-ouderdomme. Onlangse studies het egter getoon dat verhoogde plantdigthede die gemiddelde MOE van verskeie naaldhoutspesies kan verbeter. Die doelwitte van hierdie studie was om die effek van Pinus patula bosbestuursregimes, gebaseer op hoër aanvanklike plantdigthede, op die landverwagtingswaarde en stamvorm te evalueer. Stamvorm het 'n groot invloed op volume -en waardeherwinning in saagmeule en die invloed van stamvorm-eienskappe kan oorweeg word wanneer boomwaardes bereken word met die gebruik van sagtewareprogramme soos Simsaw. Hierdie studie is uitgevoer met behulp van 'n 18-jarige Pinus patula eksperimentele spasiëringproef geleë naby Barberton op die Mpumalanga platorand. Die eksperiment het bestaan uit twee herhalings van vier plantdigthede (403, 1097, 1808 en 2981 stamme per hektaar). Stamvorm-eienskappe (ovaalvormigheid, kromming, sinuositeid, onderentverdikking, en spitsing) van elke spasiëringsbehandeling is beoordeel met Lidar skanderingsdata. Die proef is afgekap en stompe verwerk in strukturele hout wat vernietigend getoets was vir MOE en die breekmodulus. Die plank MOE, tesame met saagsimulasieresultate, is gebruik om 'n stomp waardeherwinning vir elke stompklas uit elke spasiëringsbehandeling te bereken. Suid-Afrikaanse bosbou kostedata is gebruik om die landverwagtingswaarde vir 'n verskeidenheid van plantdigtheidbehandelings en dunning regimes te bereken. Spasiëring behandeling het 'n beduidende effek op al vyf stamvorm-eienskappe gehad. Oor die onderste nege meter van die stam het die laer spasiëringbehandelings (403 en 1 097 spha) ‘n gemiddelde kromming van 132.1 en 109.3 mm onderskeidelik gehad terwyl die hoër plantdigthede (1 808 en 2 981 spha) gemiddelde kromming van 76.4 en 82.1 mm onderskeidelik gehad het. Spitsing en onderentverdikking het ook 'n dalende tendens van 403 spha na 2 981 spha gehad. Ovaalvormigheid, in teenstelling, het verhoog met toenemende plantdigtheid en ook verhoog met toenemende hoogte. Daar was 'n toename in gemiddelde MOE van hout met toenemende plantdigtheid. Die strukturele graadherwinning het ook toegeneem met plantdigtheid. Dit het gelei tot verhoogde waardeherwinning vir die ooreenstemmende stompklasse, met verhoogde plantdigtheid. Die beste bosbestuurregimes vir elk van die drie laer plantdigthede (403, 1 097, en 1 808 spha) het landverwagtingswaardes relatief naby aan mekaar gehad. Die beste landverwagtingswaarde was van 'n spasiëringbehandeling van 1 808 spha, gedun op ouderdom 12 tot 300 spha, en kaalgekap op ouderdom 19 (R47 693.02/ha) die tweede beste bosbestuursregime was vir die 1 097 spha plantdigtheid, gedun tot 250 spha op ouderdom 13, en kaalgekap op ouderdom 18 (R46 677.59/ha). Ten spyte van die resultate wat toon dat hoër plantdigthede beter waardeherwinning vir soortgelyke stompklasse gee, was die beste landverwagtingswaarde nie verkry vanaf die hoogste plantdigtheid nie, maar vanaf 'n medium plantdigtheid en 'n laat dunning