Abstract：
A better understanding of the underlying ecological mechanisms of diversity-biomass relationships in forest layers (i.e., overstory and understory) is critical to understand the importance of vertical stratification to the functioning of forest ecosystems. However, it is not clear how multiple abiotic (i.e., climate and geography) and biological (i.e., biodiversity, functional characteristics, and stand structural complexity) factors simultaneously determine the aboveground biomass (AGB) of each individual forest stratum. We used data on 156,270 trees from 1986 plots in North China to explore the relationships among biological diversity, plant functional traits, stand structure, climate and topography on variation in AGB of each stratum. The results showed that different biological factors determined the AGB of overstory and understory, and thus indicating different underlying ecological mechanisms in temperate forests. The effects of forest biodiversity on AGB were only significant in understory stratum. In the overstory of the forest, forests with high tree-size dimension inequality and high dominant tree height had larger AGB, hence mass ratio effect and stand structure complexity were the main ecological mechanisms for high biomass. In understory, diversity and overstory attributes were the main factors affecting biomass. Tree height and AGB of the overstory reduced the AGB of the understory layer. In consequence overstory attributes and niche complementation were the main ecological mechanisms in the understory. The overstory exerted influence on the understory through resource quantity and resource heterogeneity. Our findings have important implications for carbon management, enhancement of forest functions and sustainable forest management in temperate forests.
摘要：
更好地理解森林层多样性-生物量关系的潜在生态机制(即，林上和林下）对于了解垂直分层对森林生态系统功能的重要性至关重要。然而,目前尚不清楚多重非生物(即，气候和地理)和生物(即，生物多样性,功能特征，和林分结构复杂性）因素同时决定了每个林层的地上生物量（AGB）。我们使用华北地区1986年地块的156,270棵树木的数据来探索生物多样性之间的关系，植物功能性状，支架结构,气候和地形对每个地层AGB变化的影响。结果表明，不同的生物因素决定了林下和林下的AGB，从而表明温带森林不同的潜在生态机制。森林生物多样性对AGB的影响仅在林下地层中显著。在森林的故事中，具有高树大小维度不等式和高优势树高的森林具有较大的AGB，因此，质量比效应和林分结构复杂性是高生物量的主要生态机制。在地下，多样性和越层属性是影响生物量的主要因素。树高和林层的AGB降低了林下层的AGB。因此，林下属性和生态位互补是林下的主要生态机制。越层通过资源数量和资源异质性对越层产生影响。我们的发现对碳管理具有重要意义，增强温带森林的森林功能和可持续森林管理。
