Data from: The value of biodiversity for the functioning of tropical forests: insurance effects during the first decade of the Sabah biodiversity experiment

One of the main environmental threats in the tropics is selective logging, which has degraded large areas of forest. In southeast Asia, enrichment planting with seedlings of the dominant group of dipterocarp tree species aims to accelerate restoration of forest structure and functioning. The role of tree diversity in forest restoration is still unclear, but the ‘insurance hypothesis’ predicts that in temporally and spatially varying environments planting mixtures may stabilize functioning owing to differences in species traits and ecologies. To test for potential insurance effects, we analyse the patterns of seedling mortality and growth in monoculture and mixture plots over the first decade of the Sabah biodiversity experiment. Our results reveal the species differences required for potential insurance effects including a trade-off in which species with denser wood have lower growth rates but higher survival. This trade-off was consistent over time during the first decade, but growth and mortality varied spatially across our 500 ha experiment with species responding to changing conditions in different ways. Overall, average survival rates were extreme in monocultures than mixtures consistent with a potential insurance effect in which monocultures of poorly surviving species risk recruitment failure, whereas monocultures of species with high survival have rates of self-thinning that are potentially wasteful when seedling stocks are limited. Longer-term monitoring as species interactions strengthen will be needed to more comprehensively test to what degree mixtures of species spread risk and use limited seedling stocks more efficiently to increase diversity and restore ecosystem structure and functioning.热带地区最主要的环境胁迫因子之一为选择性采伐，该活动已造成大面积森林退化。在东南亚地区，采用优势龙脑香科（dipterocarp）树种幼苗开展的补植造林，旨在加速森林结构与生态功能的恢复。树木多样性在森林恢复中的作用目前仍不明确，但‘保险假说（insurance hypothesis）’指出，在时空动态变化的环境中，混植群落可借助不同物种的性状与生态位差异，维持生态功能的稳定性。为验证潜在的保险效应，本研究基于沙巴生物多样性实验（Sabah biodiversity experiment）前十年的监测数据，分析了单作与混作样地内的幼苗死亡率与生长模式。研究结果揭示了潜在保险效应所需的物种间差异，其中包含一项关键权衡：木材密度更高的树种生长速率更低，但存活率更高。该权衡关系在实验前十年间始终保持稳定，但本500公顷实验样地内的生长与死亡率存在空间异质性，不同物种对环境变化的响应模式各不相同。总体而言，单作样地的平均存活率相较于混作样地更为极端，这与潜在的保险效应相符：存活率较低的物种单作面临种群更新失败的风险，而存活率较高的物种单作则会产生自疏现象，在幼苗资源有限的情况下，这种自疏可能造成资源浪费。随着物种间相互作用不断增强，需开展更长期的监测，以全面验证物种混播在多大程度上能够分散风险、更高效地利用有限的幼苗资源，从而提升群落多样性并恢复生态系统结构与功能。