Studies on the phenotypic variation in growth stress intensity and its association with tree and wood properties of South African grown Eucalyptus grandis (Hill ex Maiden)

[摘要] ENGLISH ABSTRACT:The level of growth stress in the stems of Eucalyptus grandistrees is apparently not determined by environmental factors toany great extent. A significant positive relationship was foundbetween level of growth stress and rate of growth, but the latteraccounted for only a small proportion of the enormous variationthat characteristically exists among plantation grown trees. Itmay, however, explain to some extent why trees on poor qualitysites tend to develop less end-splitting in their logs ascompared to those from better quality sites.Seasonal fluctuations in the level of growth stress were observed.Attempts to explain these fluctuations in terms ofweather patterns and soil moisture content yieldedcontradictory results. Although not quantitativelythere was some evidence to suggest that the level ofproved,growthstress is intensified in actively growing trees during periods ofsevere soil moisture deficit.Studies on open- and control-pollinated material indicated a verydefinite genetic variation among families. A narrow-senseheritability estimate of 0,56 was obtained. The geneticmanipulation of growth stress therefore seems to const1tute themost promising means of growth stress reduction in trees of thisspecies, and it can be done irrespective of tree characteristics.Since a poor relationship was found between growth stressintensity and rate of growth, the selection for reduced level ofgrowth stress and increased volume growth can be employedsimultaneously.Marked differences in awood density were foundgrowth stress intensities.number of anatomical features andamong trees of widely differentResults suggested that the genetic reduction of the level of growth stress in a tree improvementprogramme would result in a reduction in the pith-to-bark wooddensity and fibre length gradients, causing lower values in theouter parts of the stem for both these properties. Since theseproperties are the most widely usedthis implies that the selection forindices for wood quality,reduced level of growthstress would, apart for a reduction in splitting, result inreduced within-tree variability in wood quality.Furthermore,characteristicsstress suggestthe observedbetween treesthat anatomicaldifferences in anatomicalof different levels of growthdeterminations could be usedas an effective means to separate low-stressed trees fromhigh-stressed trees. Results indicated that the inherentpotential of a tree to generate growth stress of aparticular level may even be assessed at a fairly young agefrom the anatomical characteristics of the wood. However,further research is needed to quantify this in more exact termsbefore they can be used for predicting level o.f growth stresswith sufficient precision.

[发布机构] Stellenbosch University