Tree diversity across multiple scales and environmental heterogeneity promote ecosystem multifunctionality in a large temperate forest region

Aim: Biodiversity across different scales provides multidimensional
insurance for ecosystem functioning. Although the positive effects of
local scale (α-diversity) biodiversity on ecosystem multifunctionality are
widely accepted, species turnover across communities (β-diversity) which
is often an important driver of ecosystem functioning did not receive the
same attention. This study broadens the understanding of how multiple
attributes of biodiversity maintain ecosystem multifunctionality from
local to regional scales, across diverse environmental gradients.
Location: North-eastern China. Time period: 2017. Major taxa studied:
Woody plants. Methods: We estimate ecosystem multifunctionality using both
averaging and modified multiple thresholds (50%, 70% and 90%) approaches.
Multiple dimensions of biodiversity across varying spatial scales were
measured within the framework of Hill‒Chao numbers. Linear and nonlinear
models were used to evaluate the optimal patterns of multifunctionality
and biodiversity along the latitude. Using variance decomposition,
structural equation modeling and linear mixed models, we explored how
multiple attributes of tree diversity at varying spatial scales affect
multifunctionality, and how these relationships are modulated by
environmental drivers. Results: Our results show that multifunctionality
decreased with increasing latitude, mirroring the pattern of tree
diversity along latitudinal gradients. Phylogenetic β-diversity and
species α-diversity emerged as crucial diversity indices for sustaining
multifunctionality in these temperate forests. Soil and climatic
conditions had either direct effects on multifunctionality, or indirect
ones mediated by tree diversity. Environmental heterogeneity played a
pivotal role in maintaining high levels of multifunctionality, exerting
influence both directly and indirectly via phylogenetic β-diversity. Main
conclusions: This study underscores the positive effects of biodiversity
on multifunctionality across multiple dimensions. Based on our findings,
we conclude that any design of a forested landscape that is aimed at
maximizing multifunctionality should consider maintaining high local
diversity as well as forest community heterogeneity at varying scales.

研究目的：不同尺度的生物多样性为生态系统功能提供多维保障。尽管局地尺度的α多样性（α-diversity）对生态系统多功能性的积极效应已被广泛认可，但群落间的物种周转即β多样性（β-diversity）——这通常是生态系统功能的重要驱动因子——却未得到同等程度的关注。本研究旨在深化对生物多样性多维度属性如何维持从局地到区域尺度、跨越多样环境梯度的生态系统多功能性的理解。
研究区域：中国东北地区。
研究时段：2017年。
研究类群：木本植物。
方法：本研究分别采用平均法与改进的多重阈值法（50%、70%与90%阈值）估算生态系统多功能性。基于希尔-曹数（Hill‒Chao numbers）框架，测定不同空间尺度下生物多样性的多个维度。通过线性与非线性模型评估沿纬度梯度的多功能性与生物多样性的最优格局。借助方差分解、结构方程模型（structural equation modeling）以及线性混合模型，探究不同空间尺度下树木多样性的多维度属性如何影响多功能性，以及这些关系如何受环境驱动因子调控。
结果：本研究结果显示，生态系统多功能性随纬度升高而降低，这与树木多样性沿纬度梯度的分布格局相一致。系统发育β多样性与物种α多样性成为维持这些温带森林多功能性的关键多样性指数。土壤与气候条件既对多功能性产生直接效应，也可通过树木多样性介导间接影响。环境异质性在维持高水平多功能性中发挥关键作用，其既可直接作用于多功能性，也可通过系统发育β多样性产生间接调控效应。
主要结论：本研究强调了多维度生物多样性对生态系统多功能性的积极效应。基于本研究结果，我们认为，任何旨在最大化多功能性的森林景观设计，都应兼顾维持高局地多样性以及不同尺度下的森林群落异质性。