African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals affect the relative abundance of trees and grasses. However, savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages—declining wildlife populations and their displacement by livestock—may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and was consumed in bulk by native browsers during experimental cafeteria trials. In contrast, domesticated ungulates rarely ate lianas. When we experimentally excluded all large herbivores for periods of 8 to 17 y (simulating extirpation), liana abundance increased dramatically, with up to 75% of trees infested. Piecewise exclusion of different-sized herbivores revealed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but herbivores quickly cleared lianas from trees after the removal of 18-y-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without herbivores, the long-term equilibrium could be either endemic (liana–tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by replacing wildlife with livestock.

非洲稀树草原是各种大型哺乳动物群落的最后据点，稀树草原生态学的一个主要焦点是了解这些动物如何影响树木和草的相对丰度。然而，稀树草原支持多种植物生命形式，而人类引起的大型草食动物群落的变化——野生动物种群的减少及其被牲畜取代——可能会导致植物群落组成发生意想不到的变化。我们调查了食草如何影响藤本植物（木本藤本植物）的流行及其对东非稀树草原树木的影响。虽然稀少（<2% 的树冠面积）并且被有毒乳胶保护，但占优势的藤本植物Cynanchum viminale（夹竹桃科）被 15 种野生大型食草动物食用，并在实验性自助餐厅试验中被本地浏览者大量食用。相比之下，驯化的有蹄类动物很少吃藤本植物。当我们实验性地排除所有大型食草动物 8 到 17 年（模拟灭绝）时，藤本植物的丰度急剧增加，高达 75% 的树木被侵染。分段排除不同大小的食草动物揭示了大小类别在抑制藤本植物方面的功能互补性。藤本植物的侵扰减少了树木的生长和繁殖，但在移除 18 岁的封闭围栏（模拟野化）后，食草动物迅速清除了树木上的藤本植物。一个简单的藤本植物传染模型表明，没有食草动物，长期平衡可以是地方性的（藤本植物共存）或全藤本植物的替代稳定状态。我们得出的结论是，野生大型食草动物种群的持续减少将以很少受到关注的方式破坏许多非洲稀树草原的结构和功能，并且可能无法通过用牲畜代替野生动物来缓解。