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)
Date
1984
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT:
The level of growth stress in the stems of Eucalyptus grandis
trees is apparently not determined by environmental factors to
any great extent. A significant positive relationship was found
between level of growth stress and rate of growth, but the latter
accounted for only a small proportion of the enormous variation
that characteristically exists among plantation grown trees. It
may, however, explain to some extent why trees on poor quality
sites tend to develop less end-splitting in their logs as
compared to those from better quality sites.
Seasonal fluctuations in the level of growth stress were observed.
Attempts to explain these fluctuations in terms of
weather patterns and soil moisture content yielded
contradictory results. Although not quantitatively
there was some evidence to suggest that the level of
proved,
growth
stress is intensified in actively growing trees during periods of
severe soil moisture deficit.
Studies on open- and control-pollinated material indicated a very
definite genetic variation among families. A narrow-sense
heritability estimate of 0,56 was obtained. The genetic
manipulation of growth stress therefore seems to const1tute the
most promising means of growth stress reduction in trees of this
species, and it can be done irrespective of tree characteristics.
Since a poor relationship was found between growth stress
intensity and rate of growth, the selection for reduced level of
growth stress and increased volume growth can be employed
simultaneously.
Marked differences in a
wood density were found
growth stress intensities.
number of anatomical features and
among trees of widely different
Results suggested that the genetic reduction of the level of growth stress in a tree improvement
programme would result in a reduction in the pith-to-bark wood
density and fibre length gradients, causing lower values in the
outer parts of the stem for both these properties. Since these
properties are the most widely used
this implies that the selection for
indices for wood quality,
reduced level of growth
stress would, apart for a reduction in splitting, result in
reduced within-tree variability in wood quality.
Furthermore,
characteristics
stress suggest
the observed
between trees
that anatomical
differences in anatomical
of different levels of growth
determinations could be used
as an effective means to separate low-stressed trees from
high-stressed trees. Results indicated that the inherent
potential of a tree to generate growth stress of a
particular level may even be assessed at a fairly young age
from the anatomical characteristics of the wood. However,
further research is needed to quantify this in more exact terms
before they can be used for predicting level o.f growth stress
with sufficient precision.
Description
Thesis (PhD)--University of Stellenbosch, 1984.
Keywords
Eucalyptus grandis, Trees -- Growth, Phenotypic plasticity