Data from: Disentangling relationships between plant diversity and decomposition processes under forest restoration

1. Biodiversity has been elucidated to be one of the major factors sustaining ecosystem functioning. The vast majority of studies showing a relationship between biodiversity and ecosystem functioning have come from experiments, and this knowledge has not yet been applied to most real-world cases of conservation and management. This is especially true in forest ecosystems, characterized by the dominance of long-lived organisms (trees) and high levels of structural complexity and environmental heterogeneity. 2. To apply biodiversity-function relationships to actual forest management, there are several issues to be considered. These include employing a cross-taxon perspective, as some functions (e.g. soil biogeochemical processes) cannot be maintained by a narrow set of organisms, as is usually the case with experimental systems. More specifically, although the interaction between above- and below-ground diversity is important for many functions in forests, there are few studies that evaluated the roles of diversity in both subsystems in a manner that could be informative in practice. 3. To evaluate the roles of above- and below-ground diversity to support natural soil ecosystem functions, we conducted a decomposition experiment in the northern forests of Japan, which are currently under restoration management. The restoration area consists of mosaics of different vegetation types by various re-vegetation activities and establishment of ungulate exclosures. Using structural equation modelling and linear mixed effects models, we assessed direct and indirect pathways from diversity to functions by focusing on both of taxonomic and functional diversity indices. To put our findings into practice, we utilized a trait-based approach, which provides a link between the functional consequences of human influences and ecosystem structure. 4. We found little direct effects of tree diversity on below-ground functions such as decomposition rate and litter stabilization. However, once the diversities of understorey herbaceous plants and soil fungi were considered as a possible mediating explanatory factor, we found a significant effect of tree diversity to indirectly support these functions by supporting these other types of biodiversity. Particularly, we found that the models based on functional trait diversity, rather than on taxonomic species richness, best explained the variation in below-ground processes. 5. Synthesis and applications. Forest restoration in the northern forests of Japan has had no explicit objective to restore soil functions. Nevertheless, afforestation, and the associated increase in tree diversity as a measure of forest restoration was, although often unintentionally, proven effective for the maintenance of multiple ecosystem functions, such as soil biogeochemical processes. This finding suggests a great potential for management to make local tree assemblages functionally dissimilar and diverse for the sake of supporting and enhancing fundamental ecosystem functions in forests.

1. 生物多样性已被阐明为维持生态系统功能的核心驱动因素之一。绝大多数揭示生物多样性与生态系统功能间关联的研究均来自控制实验，而该认知尚未应用于多数实际保护与管理场景中，这一情况在森林生态系统中尤为突出——森林生态系统以长寿生物（树木）为优势类群，且具备极高的结构复杂度与环境异质性。
2. 若要将生物多样性-功能关联应用于实际森林管理，需考量多项关键问题：其一，需采用跨类群视角，因为部分生态功能（如土壤生物地球化学过程）无法仅由狭窄类群的生物维持，而这正是多数实验系统的常见局限。具体而言，尽管地上与地下生物多样性的交互作用对森林诸多功能至关重要，但目前鲜有研究以具备实际应用价值的方式，同时评估了两类子系统中生物多样性的作用。
3. 为评估地上与地下生物多样性在维持自然土壤生态系统功能中的作用，我们在当前正实施恢复管理的日本北部森林开展了凋落物分解实验。该恢复区域经多种植被恢复活动与有蹄类动物禁入围栏（ungulate exclosures）的设置，形成了不同植被类型镶嵌分布的格局。本研究采用结构方程模型（structural equation modelling）与线性混合效应模型（linear mixed effects models），同时聚焦分类学与功能多样性指数，解析了生物多样性影响生态功能的直接与间接路径。为将研究成果转化为实践应用，我们采用了基于功能性状（trait）的研究方法，该方法可联结人类活动的功能效应与生态系统结构。
4. 我们发现树木多样性对分解速率、凋落物固持等地下功能的直接影响微弱。但当将林下草本植物与土壤真菌的多样性作为潜在中介解释因子纳入考量后，树木多样性可通过促进这两类生物多样性，间接对上述地下功能产生显著正向作用。尤为重要的是，相较于基于分类学物种丰富度的模型，以功能性状多样性为基础的模型能够最优解释地下生态过程的变异。
5. 综合与应用：当前日本北部森林的恢复工程并未将恢复土壤功能列为明确目标，但人工造林及作为森林恢复措施的树木多样性提升（尽管常为无意之举）已被证实可有效维持土壤生物地球化学过程等多项生态系统功能。该研究结果表明，通过优化本地树木群落的功能异质性与多样性，可有效支持并增强森林的核心生态系统功能，这一思路具备巨大的管理应用潜力。