Aboveground biomass (AGB) production is an important ecosystem function and service, especially where livestock feeding is the main human activity. Rangeland managers mainly use grazing exclusion to improve AGB in degraded arid and semiarid rangeland. However, the mechanism by which this nature-based management practice increases AGB and how it influences the mediating effects of biodiversity on AGB remain unclear and little understood. Here, we explored the mechanisms driving AGB in North African semiarid rangeland by using a variety of taxonomic, functional, and phylogenetic diversity metrics, grazing management (grazed vs. ungrazed), and soil surface components as predictors. We then compared the mediating effects of the most essential taxonomic, functional, and phylogenetic diversity measures on AGB under grazing exclusion and unrestricted grazing. We found that biodiversity contributed to up to 44% of the AGB explained variance and many attributes of plant diversity showed contrasting links to AGB. We also found that biodiversity affects AGB mainly through mass ratio (which explained more than 73% of the biotic effects on AGB) rather than complementarity. The increase in AGB under grazing exclusion was not related to an increase in species richness, but it resulted from the increasing abundance of the dominant high-functioning species. Therefore, our findings recommend the focus on dominant species when implementing grazing exclusion since they play an important role in biomass production and ecosystem functioning.

中文翻译：

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放牧排斥调节植物多样性不同组成部分对半干旱牧场生物量生产的影响

地上生物量（AGB）生产是一项重要的生态系统功能和服务，特别是在以牲畜饲养为主要人类活动的地区。牧场管理者主要利用禁牧来改善退化干旱和半干旱牧场的 AGB。然而，这种基于自然的管理实践增加 AGB 的机制以及它如何影响生物多样性对 AGB 的中介作用仍不清楚，也知之甚少。在这里，我们通过使用各种分类学、功能和系统发育多样性指标、放牧管理（放牧与未放牧）和土壤表面成分作为预测因子，探索了北非半干旱牧场 AGB 的驱动机制。然后，我们比较了放牧排斥和无限制放牧下最重要的分类学、功能和系统发育多样性措施对 AGB 的中介作用。我们发现，生物多样性对 AGB 解释方差的贡献高达 44%，并且植物多样性的许多属性与 AGB 表现出相反的联系。我们还发现生物多样性主要通过质量比影响AGB（这解释了73%以上的生物对AGB的影响）而不是互补性。禁牧条件下 AGB 的增加与物种丰富度的增加无关，而是由于优势高功能物种丰富度的增加所致。因此，我们的研究结果建议在实施放牧排除时重点关注优势物种，因为它们在生物量生产和生态系统功能中发挥着重要作用。