Abstract
Radial increases in wood specific gravity have been shown to characterize early successional trees from tropical forests. Here, we develop and apply a novel method to test whether radial increases are determined by tree age or tree size. The method compares the slopes of specific gravity changes across a short radius and a long radius of trees with eccentric trunks. If radial changes are determined by size, then the slope of the change should be the same on both radii. If radial changes are determined by age, then the slope should be greater on the short radius. For 30 trees from 12 species with eccentricity of at least 4%, the ratio of the slopes of the linear regressions of specific gravity on radial distance (short radius slope/long radius slope) was regressed on the ratio of radii lengths (long radius/short radius). The regression was highly significant, and the faster increase in specific gravity on the short radius was sufficient to compensate for the difference in radius lengths, so the specific gravity of wood along the short radius was equal to the specific gravity on the long radius at any given proportional distance on the radius. Therefore, trees that are producing xylem faster on one radius than another produce wood of comparable specific gravity on both radii at the same time, so radial increases in specific gravity are dependent on tree age, not tree size.
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Acknowledgments
This research was supported by the U.S. National Science Foundation (DEB-0639144) and the Michaux Fund of the American Philosophical Society. Sayra Navas, Ana Gómez, Sonia Vargas, Toni Soto and Jacqueline Henrot helped in extracting and measuring the cores. Luis Poveda and Nelson Zamora confirmed the species’ identifications. We gratefully acknowledge the cooperation of the Organization for Tropical Studies.
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Communicated by R. Aloni.
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Williamson, G.B., Wiemann, M.C. Age versus size determination of radial variation in wood specific gravity: lessons from eccentrics. Trees 25, 585–591 (2011). https://doi.org/10.1007/s00468-010-0535-5
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DOI: https://doi.org/10.1007/s00468-010-0535-5