Age-Dependent Radial Increases in Wood Specific Gravity of Tropical Pioneers in Costa Rica

作者：Williamson G Bruce^*; Wiemann Michael C

来源：Biotropica, 2010, 42(5): 590-597.

DOI：10.1111/j.1744-7429.2009.00618.x

• biomass
• Bursera simaruba
• Heliocarpus appendiculatus
• Ochroma pyramidale
• Trema micrantha

Wood specific gravity is the single best descriptor of wood functional properties and tree life-history traits, and it is the most important variable in estimating carbon stocks in forests. Tropical pioneer trees produce wood of increasing specific gravity across the trunk radius as they grow in stature. Here, we tested whether radial increases in wood specific gravity were dependent on a tree's diameter or its age by comparing trees of different diameters within cohorts. We cored trunks of four pioneer species in naturally regenerating, even-aged stands in the lowland, wet forests of Costa Rica. For each core, specific gravity was determined for 1-cm radial wood segments, pith to bark. Increases across the radius were evident in all four species studied, and in four different stands for one species. For any given species in a given stand, the rate of radial increase in specific gravity as a function of radial distance from the pith was greater in smaller diameter trees. As the trees in a stand represent a colonizing cohort, these results strongly suggest that the radial increases in specific gravity in lowland pioneers are associated with tree age, not with tree diameter. Furthermore, the specific gravity of the outermost wood was not associated with tree radius, further negating size dependence. One consequence of these results is that species-specific biomass estimates for trees in secondary forests are likely to be confounded by age, as diameter alone may be a poor indicator of specific gravity in individual trees for pioneers of tropical wet forests.

• 出版日期2010-9