Changes in the direction of the diversity-productivity relationship over fifteen years of stand development in a planted temperate forest

Experiments manipulating diversity in both forests and grasslands have often observed a positive diversity-productivity relationship (DPR) which tends to strengthen during plant community development. This pattern is generally attributed to an increase in niche complementarity or facilitation. Most analyses do not examine species dominance and density, which also change over time. Moreover, how neighbourhood scale interactions among tree species affect the DPR is not well understood.
We analysed growth and mortality data from the Simplex experiment, a part of the BIOTREE tree diversity experiment. Simplex consists of 36 plots each planted with four common and commercially important tree species to create a gradient of tree species evenness at two tree densities (6667 and 3556 trees ha-1). We test whether: i) the effect of evenness on total aboveground biomass productivity increase with stand development (year), ii) the effect of evenness on productivity is stronger in dense plots; iii) ...

在森林与草原群落中开展的物种多样性调控实验，常观测到正向的多样性-生产力关系（diversity-productivity relationship, DPR），且该关系往往会随植物群落的发育进程逐步增强。该格局通常被归因于生态位互补（niche complementarity）或促进作用（facilitation）的增强。多数相关分析未关注物种优势度与密度的动态变化——而二者同样会随时间推移发生改变。此外，林木物种间的邻域尺度互作如何影响多样性-生产力关系，目前仍未得到充分阐释。
本研究对隶属于BIOTREE林木多样性实验项目的Simplex实验的生长与死亡率数据展开分析。Simplex实验共包含36个样地，每个样地均种植4种常见且具有重要商业价值的林木树种，以在两种林木密度（6667株·公顷⁻¹与3556株·公顷⁻¹）下构建林木物种均匀度梯度。本研究旨在验证以下假设：i） 物种均匀度对地上总生物量生产力的影响会随林分发育时长（林龄）的增加而增强；ii） 高密度样地中，物种均匀度对生产力的影响更为显著；iii）……