Factors controlling individual branch development during early growth of an experimental plantation of Eucalyptus pilula
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ORIGINAL ARTICLE
Factors controlling individual branch development during early growth of an experimental plantation of Eucalyptus pilularis in subtropical Australia P. W. West1 · D. A. Ratkowsky2 · R. G. B. Smith1 Received: 12 June 2020 / Accepted: 18 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Key message Branch sizes and their vertical orientation increase progressively further up the lower stem to support a newly developing crown. Abstract Diameter at base, orientation, and height up the stem of live branches on the lower 5 m of tree stems were measured several times over 2.5–5.7 years of age in an experimental plantation of blackbutt (Eucalyptus pilularis) in sub-tropical eastern Australia. Stocking density at planting varied over 816–1667 stems ha-1 and rectangularity of planting (ratio of distance between rows to distance between trees within rows) over 1–6. Tree stem diameters, heights and crown dimensions were also measured. The height above ground at which branches emerged from the stem was a primary factor determining their growth; the higher they were, the greater was their diameter and the more vertical their orientation. This was believed to reflect both a need for newer branches to grow larger than older branches, to support greater amounts of foliage as the crowns expanded towards full size, and for branches to be better oriented to seek sunlight as the crowns of surrounding trees also expanded. Secondary factors determining branch size were tree size and spacing between trees, factors that are likely to interact with each other. Larger trees tended to have larger branches, to support more leaf weight in larger crowns. The direction of emergence of branches from stems seemed little affected by tree or stand characteristics at these early stages of tree development. The results did not suggest any need to modify existing pruning regimes that have been developed for fast-growing eucalypt plantations in Australia. Keywords Branching · Eucalyptus · Stocking density · Rectangularity · Pruning
Introduction The function of branches is to hold aloft the leaves of a tree to expose them to best advantage to the sunlight, so that photosynthesis may occur readily. The more foliage a tree has, and the wider the spread of its crown, the larger must its branches be to carry the weight of its leaves without breaking and to provide a sufficient area of sapwood to allow transport from the roots of the water they need.
* P. W. West [email protected] 1
Forest Research Centre, Southern Cross University, Lismore, NSW 2480, Australia
Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 98, Hobart, Tasmania 7001, Australia
2
At the point where branches emerge from a tree stem, the wood grain becomes distorted, leaving a knot embedded in it. From the point of view of commercial forestry, knots are the chief source of defect in timber that is eventually sawn from the stem; they may affect the strength of the timber or the quality of its surface
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