Woody encroachment is ubiquitous in grassy ecosystems worldwide, but its global impacts on the diversity of herbaceous plants that characterise and define these ecosystems remain unquantified. The pervasiveness of encroachment is relatively easily observed via remote sensing, but its impacts on plant diversity and richness below the canopy can only be observed via field-based studies. Via a meta-analysis of 42 field studies across tropical to temperate grassy ecosystems, we quantified how encroachment altered herbaceous species richness, and the richness of forbs, C₃ graminoids and C₄ graminoids. Across studies, the natural logarithm of the response ratio (lnRR) of herbaceous species richness ranged from −3.33 to 0.34 with 87% of encroached ecosystems negatively impacted. Assessment of the extent of encroachment, duration of encroachment, mean annual rainfall, latitude, and continent demonstrated that only extent of encroachment had relevance in the data (univariate model including a random effect of study explained 45.4% of variance). The global weighted mean lnRR of species richness decreased from −0.245 at <33% of woody cover increase, to −0.562 at 33%–66%, and to −0.962 at >66%. Continued encroachment results in substantial loss of herbaceous diversity at medium and high extents, with a loss of richness that is not replaced. Although all functional groups are significantly negatively impacted by encroachment, forb richness is relatively more sensitive than graminoid richness, and C₄ graminoid richness relatively more than C₃ graminoid richness. Although no geographic or climatic correlates had relevance in the data, encroachment as an emergent product of global change coalesces to decrease ground layer light availability, lead to loss of fire and grazers, and alter hydrology and soils. Encroachment is accelerating and grassy ecosystems require urgent attention to determine critical woody cover thresholds that facilitate diverse and resilient grassy ecosystems.

中文翻译：

---

侵占减少了全球草本生态系统中的草本植物多样性

木本侵占在全球草本生态系统中无处不在，但其对表征和定义这些生态系统的草本植物多样性的全球影响仍未量化。通过遥感可以相对容易地观察到侵占的普遍性，但它对冠层下植物多样性和丰富度的影响只能通过实地研究来观察。通过对热带到温带草地生态系统的 42 项实地研究的荟萃分析，我们量化了侵占如何改变草本物种的丰富度，以及杂草、C ₃禾本科植物和 C _{4的丰富度}禾本科。在所有研究中，草本物种丰富度的响应比 (lnRR) 的自然对数范围为 -3.33 至 0.34，87% 的被侵占生态系统受到负面影响。对侵占程度、侵占持续时间、年平均降雨量、纬度和大陆的评估表明，只有侵占程度与数据相关（包括研究随机效应的单变量模型解释了 45.4% 的方差）。物种丰富度的全球加权平均 lnRR 从 <33% 的木本覆盖增加的 -0.245 下降到 -0.562 的 33%–66% 和 -0.962 的 >66%。持续侵占导致草本多样性在中等和高度范围内大量丧失，而丰富度的损失无法弥补。尽管所有功能组都受到侵占的显着负面影响，₄禾本科植物丰富度相对高于C ₃禾本科植物丰富度。尽管数据中没有地理或气候相关性，但作为全球变化的新兴产物，侵占会降低地层光的可用性，导致火灾和食草动物的损失，并改变水文和土壤。侵占正在加速，草生态系统需要紧急关注，以确定关键的木本覆盖阈值，以促进多样化和有弹性的草生态系统。