Short-term growth responses and associated wood density fluctuations in variously irrigated Eucalyptus globulus

Cambial growth and wood properties respond to fluctuating environmental conditions. Understanding the nature of these responses is crucial to understanding their cumulative effect on the wood quality characteristics of a forest stand. This paper reports on a study conducted over a period of 31/2 years in continuously irrigated, alternately irrigated and non-irrigated Eucalyptus globulus, in which changes in wood density occurring in response to short-term growth responses were examined. The study showed that continuous irrigation led to the production of wood with significantly more homogenous density than was the case in situations, where trees experienced large fluctuations in temporal water availability. Although the trees which were not irrigated had the highest wood density overall, trees in which growth was relatively continuous tended to produce the largest volumes of wood with relatively high density, compared to trees in which periodic growth responses were caused by intermittent irrigation, in which wood density was actually reduced. This was largely due to more growth days in summer under the conditions of higher radiation, and a reduction in the number of growth events leading to the production of disproportionately large amounts of low density wood. Soil water deficits contributed to density variation in all treatments, but the effect of energy limitations became more important in continuously irrigated trees.