Data from: Biodiversity as insurance for sapling survival in experimental tree plantations

Biodiversity can insure ecosystems against declines in their functioning by increasing the mean level of ecosystem processes and decreasing the spatial or temporal variance of these processes. On this basis, mixing tree species is expected to be an effective management strategy to reduce the risk of planting failure in young plantations.
We examined the effects of biodiversity insurance on sapling survival in three tree diversity experiments across Belgium. Based on the survival scoring of 89 254 saplings, planted in 126 plots with up to four-species mixtures, we tested two hypotheses: (i) variability in plot-level survival is lower for mixtures compared to monocultures due to compensation among the species (i.e. buffering effect) and (ii) mean survival is higher due to facilitation (i.e. performance-enhancing effect).
Variation in plot-level survival decreased strongly with diversity, indicating a buffering effect. The risk of severe planting failure was reduced in mixtures because species exhibit different survival rates; therefore, mixing ensures that not all trees in the plantation are equally susceptible to environmental stressors. In contrast, the mean plot-level survival did not increase with diversity, and thus, an overall performance-enhancing effect was lacking. However, species-level analyses did show performance-enhancing effects, where some species profited from mixing while others did not.
Synthesis and applications. We conclude that biodiversity through mixing tree species insures young experimental plantations against planting failure and is therefore highly recommended as a planting management strategy. The risk of large mortality gaps is reduced if tree plantation saplings are mixed at the scale of individual trees or small cells of trees.

生物多样性（Biodiversity）可通过提升生态系统过程的平均水平、降低此类过程的空间与时间变异，保障生态系统免于功能衰退。据此，混交林木被视为降低幼龄人工林种植失败风险的有效经营策略。
我们在比利时境内开展的3项林木多样性试验中，探究了生物多样性保障效应对幼树（sapling）存活的影响。本研究基于126个样地（plot）内（最多设置4个树种的混交组合）的89254株幼树存活评分数据，检验了两项假说：（1）由于物种间的补偿作用（即缓冲效应（buffering effect）），混交林样地的存活变异程度低于纯林（monocultures）样地；（2）由于种间促进作用（即性能提升效应（performance-enhancing effect）），混交林的平均存活率更高。
样地尺度的存活变异随多样性水平提升显著降低，印证了缓冲效应。混交林的严重种植失败风险有所降低，这是因为不同树种的存活率存在差异，混交可确保人工林内不会所有林木对环境胁迫的敏感性都一致。与之相反，样地平均存活率并未随多样性提升而升高，因此未观测到整体的性能提升效应。但物种尺度的分析结果显示存在性能提升效应：部分树种可从混交中获益，而其余树种则无此效果。
综合与应用。本研究结论表明，通过混交林木实现的生物多样性可为实验性幼龄人工林抵御种植失败提供保障，因此该经营策略值得大力推广。若以单株林木或小型林木单元为尺度进行幼树混交，可有效降低大规模死亡率差异的风险。