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.

热带树木物种内部及跨物种的木材比重（wood specific gravity, WSG）变异与热带森林演替过程中的植被变化之间的关联，目前尚未得到充分研究。本研究针对哥斯达黎加东北部沿演替时间序列的8个长期样地，对91个物种的木材比重展开了调查。木材比重沿茎干半径的径向变化，可通过沿茎半径的变化速率（斜率）进行表征。在74个物种中，有42个物种呈现出显著的径向变化：其中37个物种的木材比重从木质部内部向外部递增，剩余5个物种则呈现递减趋势。内部木材比重低于0.5的物种通常表现为径向递增，而内部木材比重高于0.7的物种则多呈现径向递减。按横截面积加权的木材比重（wood specific gravity weighted by cross-sectional area, wWSG）在不同物种间的变异幅度达4倍。次生林专性物种的wWSG、内部及外部木材比重均低于老龄林专性物种，而径向变化斜率更高；演替广适性物种的性状值则介于两类专性物种之间。在同时在次生林与老龄林样地中均采样的18个物种中，有4个物种（占比22%）在不同林型间的wWSG存在显著差异。在33个被广泛采样的物种中，7个物种（占比21%）的茎直径对wWSG存在显著影响。次生林样地的林分水平wWSG低于老龄林样地，且径向递增趋势也更为显著。对于呈现径向递增且木材比重较低的物种，采用未加权木材比重计算得到的单木生物量，相较于基于wWSG的计算结果，被大幅低估。木材比重在多个尺度上随演替阶段发生变异：包括物种内部、演替专性类群之间，以及不同林龄的样地之间均存在差异。热带森林演替早期和中期阶段的树木中，木材比重径向递增现象十分普遍。该性状可在演替早期赋予生长优势，并在演替后期提升对物理或生物损伤的抗性。