Experimental manipulations of tree diversity have often found overyielding in mixed-species plantations. While most experiments are still in the early stages of stand development, the impacts of tree diversity are expected to accumulate over time. Here, I present findings from a 31-year-old tree diversity experiment (as of 2018) in Japan. I find that the net diversity effect on stand biomass increased linearly through time. The species mixture achieved 64% greater biomass than the average monoculture biomass 31 years after planting. The complementarity effect was positive and increased exponentially with time. The selection effect was negative and decreased exponentially with time. In the early stages (≤ 3 years), the positive complementarity effect was explained by enhanced growths of early- and mid-successional species in the mixture. Later on (≥ 15 years), it was explained by their increased survival rates owing to vertical spatial partitioning — i.e. alleviation of self-thinning via canopy stratification. The negative selection effect resulted from suppressed growths of late-successional species in the bottom layer. The experiment provides pioneering evidence that the positive impacts of diversity-driven spatial partitioning on forest biomass can accumulate over multiple decades. The results indicate that forest biomass production and carbon sequestration can be enhanced by multispecies afforestation strategies.

中文翻译：

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由于空间划分，树木多样性对森林生产力的影响随时间而增加

在混合物种的人工林中，经常发现对树木多样性的实验性操纵过分。虽然大多数实验仍处于林分发育的早期阶段，但预计树木多样性的影响会随着时间而累积。在这里，我介绍了日本一项31年之久的树木多样性实验（截至2018年）的发现。我发现净生物多样性对林分生物量的影响随时间线性增加。种植后31年，该物种混合物的生物量比平均单培养生物量高64％。互补效应为正，并随时间呈指数增长。选择效果为负，并随时间呈指数下降。在早期（≤3年），积极的互补效应可以通过混合物中早期和中期成功种的生长加快来解释。后来（≥15年），可以解释为它们由于垂直空间划分而增加了存活率，即通过树冠分层减轻了自我变薄。负选择效应是由于底层中后期成功种的生长受到抑制。该实验提供了开创性证据，表明多样性驱动的空间划分对森林生物量的积极影响可以累积数十年。结果表明，通过多物种造林策略可以提高森林生物量的生产和碳固存。负选择效应是由于底层中后期成功种的生长受到抑制。该实验提供了开创性证据，表明多样性驱动的空间划分对森林生物量的积极影响可以累积数十年。结果表明，通过多物种造林策略可以提高森林生物量的生产和碳固存。负选择效应是由于底层中后期成功种的生长受到抑制。该实验提供了开创性证据，表明多样性驱动的空间划分对森林生物量的积极影响可以累积数十年。结果表明，通过多物种造林策略可以提高森林生物量的生产和碳固存。