Tree Diversity Enhances Stand Carbon Storage but Not Leaf Area in a Subtropical Forest.

Research about biodiversity–productivity relationships has focused on herbaceous ecosystems, with results from tree field studies only recently beginning to emerge. Also, the latter are concentrated largely in the temperate zone. Tree species diversity generally is much higher in subtropical and tropical than in temperate or boreal forests, with reasons not fully understood. Niche overlap and thus complementarity in the use of resources that support productivity may be lower in forests than in herbaceous ecosystems, suggesting weaker productivity responses to diversity change in forests. We studied stand basal area, vertical structure, leaf area, and their relationship with tree species richness in a subtropical forest in south-east China. Permanent forest plots of 30 x 30 m were selected to span largely independent gradients in tree species richness and secondary successional age. Plots with higher tree species richness had a higher stand basal area. Also, stand basal area increases over a 4-year census interval were larger at high than at low diversity. These effects translated into increased carbon stocks in aboveground phytomass (estimated using allometric equations). A higher variability in tree height in more diverse plots suggested that these effects were facilitated by denser canopy packing due to architectural complementarity between species. In contrast, leaf area was not or even negatively affected by tree diversity, indicating a decoupling of carbon accumulation from leaf area. Alternatively, the same community leaf area might have assimilated more C per time interval in more than in less diverse plots because of differences in leaf turnover and productivity or because of differences in the display of leaves in vertical and horizontal space. Overall, our study suggests that in species-rich forests niche-based processes support a positive diversity–productivity relationship and that this translates into increased carbon storage in long-lived woody structures. Given the high growth rates of these forests during secondary succession, our results further indicate that a forest management promoting tree diversity after disturbance may accelerate CO2 sequestration from the atmosphere and thus be relevant in a climate-change context.

关于生物多样性 - 生产力关系的研究主要集中在草本生态系统，而关于乔木的实地研究结果直到最近才开始出现。此外，后者主要集中在温带地区。亚热带和热带的树种多样性通常比温带或寒带森林高得多，其原因尚未完全清楚。生态位重叠以及因此在支持生产力的资源利用上的互补性在森林中可能比在草本生态系统中更低，这表明森林对多样性变化的生产力响应较弱。我们研究了中国东南部一片亚热带森林的林分断面积、垂直结构、叶面积以及它们与树种丰富度的关系。选取了30×30米的永久性森林样地，以涵盖树种丰富度和次生演替年龄大致独立的梯度。树种丰富度较高的样地具有较高的林分断面积。此外，在4年的调查间隔内，高多样性样地的林分断面积增加量大于低多样性样地。这些影响转化为地上植物生物量中碳储量的增加（使用异速生长方程估算）。在多样性更高的样地中，树高的变异性更大，这表明由于物种之间的结构互补性，更密集的冠层结构促进了这些影响。相比之下，叶面积不受树种多样性的影响，甚至呈负相关，这表明碳积累与叶面积脱钩。或者，由于叶片周转率和生产力的差异，或者由于叶片在垂直和水平空间的分布差异，相同的群落叶面积在多样性更高的样地中可能在每个时间间隔内同化更多的碳。总体而言，我们的研究表明，在物种丰富的森林中，基于生态位的过程支持正的多样性 - 生产力关系，并且这转化为长寿木本结构中碳储存的增加。鉴于这些森林在次生演替过程中的高生长率，我们的研究结果进一步表明，在干扰后促进树木多样性的森林管理可能会加速从大气中吸收二氧化碳，因此在气候变化背景下具有重要意义。