The replacement of grasses by shrubs or bare ground (xerification) is a primary form of landscape change in drylands globally with consequences for ecosystem services. The potential for wild herbivores to trigger or reinforce shrubland states may be underappreciated, however, and comparative analyses across herbivore taxa are sparse. We sought to clarify the relative effects of domestic cattle, native rodents, native lagomorphs, and exotic African oryx (Oryx gazella) on a Chihuahuan Desert grassland undergoing shrub encroachment. We then asked whether drought periods, wet season precipitation, or interspecific grass–shrub competition modified herbivore effects to alter plant cover, species diversity, or community composition. We established a long‐term experiment with hierarchical herbivore exclosure treatments and surveyed plant foliar cover over 25 years. Cover of honey mesquite (Prosopis glandulosa) proliferated, responding primarily to climate, and was unaffected by herbivore treatments. Surprisingly, cattle and African oryx exclusion had only marginal effects on perennial grass cover at their current densities. Native lagomorphs interacted with climate to limit perennial grass cover during wet periods. Native rodents strongly decreased plant diversity, decreased evenness, and altered community composition. Overall, we found no evidence of mammalian herbivores facilitating or inhibiting shrub encroachment, but native small mammals interacting with climate drove dynamics of herbaceous plant communities. Ongoing monitoring will determine whether increased perennial grass cover from exclusion of native lagomorphs and rodents slows the transition to a dense shrubland.

中文翻译：

---

多种哺乳动物食草动物和气候对奇瓦瓦沙漠草地-灌木地过渡的影响


用灌木或裸露地面取代草（干旱化）是全球干旱地区景观变化的主要形式，对生态系统服务产生影响。然而，野生食草动物触发或加强灌木丛状态的可能性可能被低估了，并且对食草动物分类群的比较分析很少。我们试图阐明家牛、本地啮齿动物、本地兔形目动物和外来非洲羚羊 （Oryx gazella） 对正在遭受灌木侵占的奇瓦瓦沙漠草原的相对影响。然后，我们询问了干旱期、雨季降水或种间草灌木竞争是否改变了食草动物的影响，从而改变了植物覆盖、物种多样性或群落组成。我们建立了一个分层食草动物封闭处理的长期实验，并调查了超过 25 年的植物叶面覆盖率。蜂蜜牧豆树 （Prosopis glandulosa） 的覆盖率激增，主要对气候做出反应，并且不受食草动物处理的影响。令人惊讶的是，牛和非洲羚羊的排斥对当前密度的多年生草覆盖率的影响很小。本地兔形目与气候相互作用，以限制潮湿时期多年生草的覆盖。本地啮齿类动物强烈降低了植物多样性，降低了均匀度，并改变了群落组成。总体而言，我们没有发现哺乳动物食草动物促进或抑制灌木侵占的证据，但本地小型哺乳动物与气候的相互作用推动了草本植物群落的动态。持续的监测将确定因排除本地兔形目和啮齿动物而增加的多年生草覆盖率是否会减缓向茂密灌木丛的过渡。