Abstract
The present study aims to compare the allometry and wood density of Goupia glabra Aubl. (Goupiaceae) in two different terra-firme sites in Amazonian forest. A total of 65 trees ≥ 10 cm DBH was sampled in both sites, with 39 trees in Nova Olinda do Norte (NOlinda, near the Amazon River) and 29 trees in Apuí (near the southern edge of the Amazon forest). Except for the relationship between DBH (diameter at breast height) and Ht (total height), allometric relationships for G.glabra differed significantly between sites. Apuí had lower intercept and greater slope for log10 (DBH) versus log10 (Hs - stem height), and, conversely, greater intercept and lower slope for log10 (DBH) versus log10 (Ch - crown height). The slope differed significantly between the sites for DBH versus Cd (crown diameter), with greater slope found for NOlinda. Mean basic wood density in Apuí was 8.8% lower than in NOlinda. Our findings highlight the variation in adaptive strategy of G. glabra due to environmental differences between sites. This is probably because of different canopy-understory light gradients, which result in differentiation of resource allocation between vertical and horizontal growth, which, in turn, affects mechanical support related to wood density. We also hypothesize that differences in soil fertility and disturbance regimes between sites may act concomitantly with light.
Highlights
In tropical forests light is one of the most limiting resources for tree growth
Since there is a gradient of light availability ranging from a low light level in the understory to a high one in the forest canopy, allometric differences are expected among tropical tree species because of their differences in light requirements (Chazdon and Fetcher, 1984)
When diameter at breast height (DBH) was regressed against the two variables that compose Ht (Hs and crown length (Ch)), both intercepts and slopes were significantly different between sites (Figure 2b, c)
Summary
In tropical forests light is one of the most limiting resources for tree growth. The ability of a tree to assimilate light energy depends on the relationships between the size of the tree (height and diameter) and crown size (both vertical and horizontal dimensions), i.e., the tree allometry – the spatial distribution of its components along the verticalBraz. Since there is a gradient of light availability ranging from a low light level in the understory to a high one in the forest canopy, allometric differences are expected among tropical tree species because of their differences in light requirements (Chazdon and Fetcher, 1984). In this sense, low-statured and shade-tolerant understory tree species, which are adapted to low light environments for establishment and growth, tend to have proportionally wider and shallower crowns in order to (i) increase their ability to assimilate light along the horizontal light gradient and (ii) avoid self-shedding. Shade-intolerant pioneer species, which only grow in gaps and/or are highly light demanding, invest proportionally more in height growth, increasing crown depth while reducing crown horizontal expansion (King, 1996; Thomas, 1996; Sterck et al, 2001; Alves and Santos, 2002)
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