AOBPreview published online on May 19, 2009
Annals of Botany, doi:10.1093/aob/mcp118
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Wood density and its radial variation in six canopy tree species differing in shade-tolerance in western Thailand
1 Institute of Botany, University of Natural Resources and Applied Life Sciences, 33 Gregor Mendel Strasse, Vienna 1180, Austria
2 Institute of Wood Science and Technology, University of Natural Resources and Applied Life Sciences, Vienna 1180, Austria
3 Monash University, School of Biological Sciences, Clayton, Victoria 3800, Australia
4 National Parks, Wildlife, and Plant Conservation Department, Chatuchak Bangkok 10900, Thailand
* For correspondence. E-mail charles.nock{at}gmail.com
Received: 19 February 2009 Returned for revision: 17 March 2009 Accepted: 9 April 2009
Background and Aims: Wood density is a key variable for understanding life history strategies in tropical trees. Differences in wood density and its radial variation were related to the shade-tolerance of six canopy tree species in seasonally dry tropical forest in Thailand. In addition, using tree ring measurements, the influence of tree size, age and annual increment on radial density gradients was analysed.
Methods: Wood density was determined from tree cores using X-ray densitometry. X-ray films were digitized and images were measured, resulting in a continuous density profile for each sample. Mixed models were then developed to analyse differences in average wood density and in radial gradients in density among the six tree species, as well as the effects of tree age, size and annual increment on radial increases in Melia azedarach.
Key Results: Average wood density generally reflected differences in shade-tolerance, varying by nearly a factor of two. Radial gradients occurred in all species, ranging from an increase of (approx. 70%) in the shade-intolerant Melia azedarach to a decrease of approx. 13% in the shade-tolerant Neolitsea obtusifolia, but the slopes of radial gradients were generally unrelated to shade-tolerance. For Melia azedarach, radial increases were most-parsimoniously explained by log-transformed tree age and annual increment rather than by tree size.
Conclusions: The results indicate that average wood density generally reflects differences in shade-tolerance in seasonally dry tropical forests; however, inferences based on wood density alone are potentially misleading for species with complex life histories. In addition, the findings suggest that a ‘whole-tree’ view of life history and biomechanics is important for understanding patterns of radial variation in wood density. Finally, accounting for wood density gradients is likely to improve the accuracy of estimates of stem biomass and carbon in tropical trees.
Key words: Radial gradients, shade-tolerance, tree biomass estimates, tree rings, tropical trees, wood density