New Zealand Journal of Botany abstract

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B96051

Received 19 July 1996; accepted 25 August 1997

New Zealand Journal of Botany, 1998, Vol. 36: 135-140

0028-825X/98/3601-135 $7.00 (c) The Royal Society of New Zealand 1998

Branch morphology and abscission in kauri, Agathis australis (Araucariaceae)

VIVIENNE R. WILSON*
KEVIN S. GOULD
PETER H. LOVELL

Plant Science Research Group
School of Biological Sciences
The University of Auckland
Private Bag 92019
Auckland, New Zealand

JENNY AITKEN-CHRISTIE

Carter Holt Harvey Forests Ltd
New Zealand Forest Biotechnology Centre
P. O. Box 2463
Rotorua, New Zealand
*Present address: Centre for Forest Biology, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada.

Abstract  Agathis australis is unusual in that self-pruning of branches occurs. This capability persists throughout the life of the tree and all branches have this potential. Four morphologically different branch types were identified. The first-formed (early) branches on kauri saplings are longer, more slender, and longer lived than those formed later. They also have a juvenile leaf form whereas the later-formed branches on the saplings have a transitional leaf form. In the mature tree, the adult support branches bear foliage branches, which have the shortest life span of all the branch types. Analysis of shed branches showed that both early- and late-formed sapling branches have a greatly enlarged branch diameter at the base, a smooth separation face, and a reduction in cross-sectional area of vascular tissue at the point of separation when the branch abscises. In contrast, adult foliage branches show little indication of swelling of the branch base, no reduction of vascular tissue, a rough separation face, and broken vascular tissue after abscission, apparently from mechanical force breaking the wood. It appears that mechanical force is necessary for abscission to occur in adult foliage branches. When early-formed sapling branches were cut back to 50 mm stumps, the stumps abscised within six weeks in almost all cases. This occurred irrespective of the time of year that the treatment was carried out. Intact control branches did not abscise within the same time period.

Keywords  kauri; Agathis australis; branch abscission; self-pruning

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