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Ecology |
Department of Biology and 3Department of Physics, Universiti Brunei Darussalam, Jalan Tungku Link, Bandar Seri Begawan, Brunei Darussalam, Borneo
ABSTRACT
In rainforests, trunk size, strength, crown position, and geometry of a tree affect light interception and the likelihood of mechanical failure. Allometric relationships of tree diameter, wood density, and crown architecture vs. height are described for a diverse range of rainforest trees in Brunei, northern Borneo. The understory species follow a geometric model in their diameter–height relationship (slope, β = 1.08), while the stress–elasticity models prevail (β = 1.27–1.61) for the midcanopy and canopy/emergent species. These relationships changed with ontogeny, especially for the understory species. Within species, the tree stability safety factor (SSF) and relative crown width decreased exponentially with increasing tree height. These trends failed to emerge in across-species comparisons and were reversed at a common (low) height. Across species, the relative crown depth decreased with maximum potential height and was indistinguishable at a common (low) height. Crown architectural traits influence SSF more than structural property of wood density. These findings emphasize the importance of applying a common reference size in comparative studies and suggest that forest trees (especially the understory group) may adapt to low light by having deeper rather than wider crowns due to an efficient distribution and geometry of their foliage.
Key Words: adaptation comparative studies standardized major axis regression tree adult stature tree architecture wood density
Received for publication April 15, 2007. Accepted for publication October 16, 2007.
FOOTNOTES
1 The authors thank the staff of the UBD Kuala Belalong Field Studies Centre for granting access to the permanent plot and for logistic support. D. Falster and I. Wright provided freely and online the SMA regression software used. Thanks also go to A. Olofinjana for thoughtful discussion on wood strength and tree mechanical design.
4 Author for all correspondence (e-mail: osunkoya{at}fos.ubd.edu.bn or Zegler_au{at}yahoo.com.au ), present address: Department of Biology, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link BE 1410 Bandar Seri Begawan, Brunei Darussalam, phone: +673-2463001 ext. 1374, fax: +673-2461502.
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