Data from: Radial changes in wood specific gravity of tropical trees: inter- and intra-specific variation during secondary succession

Variation in wood specific gravity (WSG) within and across species of
tropical trees is poorly studied in relation to vegetation change during
tropical forest succession. We investigated WSG of 91 species in eight
long-term plots along a successional chronosequence in northeastern Costa
Rica. Radial changes in WSG were described by the rate of change (slope)
along the stem radius. Significant radial changes were found in 42 of 74
species, with 37 species exhibiting increases from inner to outer wood,
and 5 exhibiting decreases. Radial increases were commonly observed in
species with inner WSG below 0.5, whereas radial decreases were observed
in species with inner WSG above 0.7. Wood specific gravity weighted by
cross-sectional area (wWSG) varied four-fold among species. Species
classified as second-growth specialists had lower wWSG, lower inner and
outer WSG, and higher slopes than old-growth specialists; successional
generalists showed intermediate trait values. Among 18 species sampled in
both second- and old-growth forests, 4 species (22%) showed significant
variation in wWSG between forest types. Of 33 widely sampled species,
seven species (21%) showed a significant effect of stem diameter on wWSG.
Second-growth plots had lower stand-level wWSG and more pronounced radial
increases than old-growth plots. Individual tree biomass for species with
radial increases and low WSG was substantially underestimated when based
on unweighted WSG compared to wWSG. Wood specific gravity varied with
successional stage at multiple levels: within species, among successional
specialist groups, and across plots of varying ages. Radial increases in
WSG are common among trees in early and intermediate stages of tropical
forest succession. This trait may confer growth advantages early in
succession and increased resistance to physical or biotic damage during
later successional stages.