School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia.
School of Biology and Environmental Science, Queensland University of Technology, Brisbane, Queensland, Australia.
Ecol Appl. 2023 Dec;33(8):e2909. doi: 10.1002/eap.2909. Epub 2023 Sep 21.
Herbivore exclusion is implemented globally to recover ecosystems from grazing by introduced and native herbivores, but evidence for large-scale biodiversity benefits is inconsistent in arid ecosystems. We examined the effects of livestock exclusion on dryland plant richness and reproductive capacity. We collected data on plant species richness and seeding (reproductive capacity), rainfall, vegetation productivity and cover, soil strength and herbivore grazing intensity from 68 sites across 6500 km of arid Georgina gidgee (Acacia georginae) woodlands in central Australia between 2018 and 2020. Sites were on an actively grazed cattle station and two destocked conservation reserves. We used structural equation modeling to examine indirect (via soil or vegetation modification) versus direct (herbivory) effects of grazing intensity by two introduced herbivores (cattle, camels) and a native herbivore (red kangaroo), on seasonal plant species richness and seeding of all plants, and the richness and seeding of four plant groups (native grasses, forbs, annual chenopod shrubs, and palatable perennial shrubs). Non-native herbivores had a strong indirect effect on plant richness and seeding by reducing vegetative ground cover, resulting in decreased richness and seeding of native grasses and forbs. Herbivores also had small but negative direct impacts on plant richness and seeding. This direct effect was explained by reductions in annual chenopod and palatable perennial shrub richness under grazing activity. Responses to grazing were herbivore-dependent; introduced herbivore grazing reduced native plant richness and seeding, while native herbivore grazing had no significant effect on richness or seeding of different plant functional groups. Soil strength decreased under grazing by cattle but not camels or kangaroos. Cattle had direct effects on palatable perennial shrub richness and seeding, whereas camels had indirect effects, reducing richness and seeding by reducing the abundance of shrubs. We show that considering indirect pathways improves evaluations of the effects of disturbances on biodiversity, as focusing only on direct effects can mask critical mechanisms of change. Our results indicate substantial biodiversity benefits from excluding livestock and controlling camels in drylands. Reducing introduced herbivore impacts will improve soil and vegetation condition, ensure reproduction and seasonal persistence of species, and protect native plant diversity.
食草动物的排除被全球用来从引入和本地食草动物的放牧中恢复生态系统，但在干旱生态系统中，大规模生物多样性益处的证据并不一致。我们研究了牲畜排除对旱地植物丰富度和繁殖能力的影响。我们收集了 2018 年至 2020 年在澳大利亚中部乔治娜金吉（Acacia georginae）林地 6500 公里范围内的 68 个地点的植物物种丰富度和播种（繁殖能力）、降雨、植被生产力和覆盖、土壤强度和食草动物放牧强度的数据。这些地点位于一个正在放牧的牛站和两个无牛的保护区。我们使用结构方程模型来检验两种引入的食草动物（牛、骆驼）和一种本地食草动物（红袋鼠）的放牧强度对季节性植物物种丰富度和所有植物的播种、四种植物群（本地草、野花、一年生 chenopod 灌木和可食用的多年生灌木）的丰富度和播种的间接（通过土壤或植被的改变）与直接（食草）影响。非本地食草动物通过减少植被地面覆盖，对植物丰富度和播种有很强的间接影响，导致本地草和野花的丰富度和播种减少。食草动物也对植物的丰富度和播种有小而负面的直接影响。这种直接影响可以通过放牧活动下一年生 chenopod 和可食用的多年生灌木丰富度的减少来解释。对放牧的反应取决于食草动物；引入的食草动物放牧减少了本地植物的丰富度和播种，而本地食草动物放牧对不同植物功能群的丰富度或播种没有显著影响。在牛放牧下土壤强度降低，但骆驼或袋鼠放牧下则没有。牛对可食用的多年生灌木的丰富度和播种有直接影响，而骆驼则通过减少灌木的丰度产生间接影响。我们表明，考虑间接途径可以提高对生物多样性受干扰影响的评估，因为仅关注直接影响可能掩盖关键的变化机制。我们的结果表明，在干旱地区，排除牲畜和控制骆驼可以带来大量的生物多样性益处。减少引入的食草动物的影响将改善土壤和植被条件，确保物种的繁殖和季节性持续存在，并保护本地植物多样性。
