Data from: Logging increases the functional and phylogenetic dispersion of understorey plant communities in tropical lowland rainforest

1. Logging is a major driver of tropical forest degradation, with severe impacts on plant richness and composition. Rarely have these effects been considered in terms of their impact on the functional and phylogenetic diversity of understorey plant communities, despite the direct relevance to community reassembly trajectories. Here, we test the effects of logging on functional traits and evolutionary relatedness, over and above effects that can be explained by changes in species richness alone. We hypothesised that strong environmental filtering will result in more clustered (under-dispersed) functional and phylogenetic structures within communities as logging intensity increases.
2. We surveyed understorey plant communities at 180 locations across a logging intensity gradient from primary to repeatedly-logged tropical lowland rainforest in Sabah, Malaysia. For the 691 recorded plant taxa, we generated a phylogeny to assess plot-level phylogenetic relatedness. We quantified 10 plant traits known to respond to disturbance (dispersal mode, fruit type, life-history mode, pollination syndrome, reproduction strategy and seed number) and affect ecosystem functioning (plant growth form, plant height, specific leaf area and wood density), and tested the influence of logging on functional and phylogenetic structure.
3. We found no significant effect of local- or landscape-scale forest canopy loss, or configuration of logging roads on species richness. By contrast, both the trait dispersion index (FDis) and net relatedness index (NRI) for phylogenetic dispersion showed strong gradients from clustered towards more randomly-assembled communities at higher logging intensity, independent of variation in species richness. All functional traits showed significant phylogenetic signals, indicating strong concordance between functional and phylogenetic dispersion.
4. Synthesis. We found a strong logging signal in the functional and phylogenetic structure of understorey plant communities, over and above species richness, but this effect was opposite to that predicted. Logging increased, rather than decreased, functional and phylogenetic dispersion in understorey plant communities. This effect was particularly pronounced for functional response traits, which directly link disturbance with plant community reassembly. Our study provides novel insight into the way logging affects understorey plant communities in tropical rainforest and highlights the importance of trait-based approaches to improve our understanding of the broad range of logging-associated impacts.

1. 森林采伐是热带森林退化的主要驱动因素之一，对植物物种丰富度与群落组成造成严重影响。尽管这些影响与林下植物群落（understorey plant communities）的重建轨迹直接相关，但此前极少有研究从其对林下植物群落功能多样性（functional diversity）与系统发育多样性（phylogenetic diversity）的影响角度开展相关探讨。本研究旨在探究，在仅由物种丰富度变化所能解释的影响之外，采伐对植物功能性状（functional traits）与进化亲缘关系的作用。我们提出假设：随着采伐强度（logging intensity）提升，强烈的环境过滤（environmental filtering）作用将导致群落内功能与系统发育结构呈现更为显著的聚集（clustered）与低分散（under-dispersed）状态。
2. 我们在马来西亚沙巴州，沿从原始林（primary forest）到反复采伐的热带低地雨林（tropical lowland rainforest）的采伐强度梯度（logging intensity gradient），于180个样点开展了林下植物群落调查。针对记录到的691个植物分类单元，我们构建了系统发育树（phylogeny）以评估样方水平的系统发育相关性（phylogenetic relatedness）。我们量化了10种已知对干扰有响应且影响生态系统功能（ecosystem functioning）的植物性状：其中响应干扰的性状包括传播方式（dispersal mode）、果实类型（fruit type）、生活史模式（life-history mode）、传粉综合征（pollination syndrome）、繁殖策略（reproduction strategy）与种子数量（seed number），影响生态系统功能的性状涵盖植物生长型（plant growth form）、植株高度（plant height）、比叶面积（specific leaf area）与木材密度（wood density），并检验了采伐对群落功能与系统发育结构的影响。
3. 研究发现，局域或景观尺度的森林冠层损失（canopy loss），以及采伐道路（logging roads）的布局，均未对物种丰富度产生显著影响。与之相反，性状分散指数（FDis）与用于表征系统发育分散度（phylogenetic dispersion）的净亲缘关系指数（NRI）均呈现显著梯度变化：随着采伐强度升高，群落结构从聚集状态逐渐转向更为随机的组合状态，且该变化与物种丰富度的变异无关。所有功能性状均表现出显著的系统发育信号（phylogenetic signals），表明功能分散度与系统发育分散度之间存在高度一致性。
4. 综合分析：我们在林下植物群落的功能与系统发育结构中发现了显著的采伐效应信号，且该效应独立于物种丰富度的变化，但与我们的预测结果恰好相反。采伐提升了而非降低了林下植物群落的功能与系统发育分散度。该效应在功能响应性状（functional response traits）中表现得尤为显著——这类性状直接将干扰与植物群落重建（plant community reassembly）联系起来。本研究为理解热带森林采伐如何影响林下植物群落提供了全新视角，并强调了基于性状的研究方法的重要性，有助于深化我们对各类采伐相关影响的认知。