Original Articles

The Relationship between Soil Water Status, Rainfall and the Growth of Eucalyptus grandis

Published in: South African Forestry Journal
Volume 156, issue 1, 1991 , pages: 49–55
DOI: 10.1080/00382167.1991.9629087
Author(s): D.I. BodenInstitute for Commercial Forestry Research, South Africa

Abstract

Available soil water is recognised as the main factor influencing the growth of commercial plantations in southern Africa. This is of strategic importance as successive rotations of demanding species such as Eucalyptus grandis may be depleting the soil water reserves leading to possible declining yields. In this study the soil water status (SWS) was measured under three plots of seven-year-old E. grandis which were part of a site preparation experiment. Tree vigour on these plots, expressed in terms of Mean Annual Increment, was recorded at 26, 16 and 6 t/ha per annum. Soil water was measured to a depth of 1,4 m at varying distances from the trees at weekly intervals for 20 months using a neutron moisture meter. Tree vigour was found to be inversely proportional to SWS. While there was a large seasonal variation in SWS, the status under the largest trees was consistently and substantially drier than under the smallest trees. Weekly measurements of tree growth indicated that the least vigorous trees were, notwithstanding their smaller crown and root system, growing marginally more quickly than the largest trees. It is assumed that the latter have utilised sufficient amounts of soil water resulting in a slowing down of their current growth.

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