Data from: Livestock activity increases exotic plant richness, but wildlife increases native richness, with stronger effects under low productivity

1.Grazing by domestic livestock is one of the most widespread land uses worldwide, particularly in rangelands, where it co-occurs with grazing by wild herbivores. Grazing effects on plant diversity are likely to depend on intensity of grazing, herbivore type, coevolution with plants and prevailing environmental conditions. 2.We collected data on climate, plant productivity, soil properties, grazing intensity and herbivore type; and measured their effects on plant species richness from 451 sites across 0.4 M km2 of semi-arid rangelands in eastern Australia. We used structural equation modelling to examine the direct and indirect effects of increasing grazing intensity by different herbivores (cattle, sheep, kangaroos, rabbits) on native and exotic plant species richness across all sites, and in subsets focusing on three woodland communities spanning a gradient in productivity. 3.Direct effects of grazing by all herbivores were strongest under low productivity but waned with increasing productivity. Increases in the intensity of recent and historic livestock grazing corresponded with greater exotic plant richness under low productivity and less native plant richness under both low and moderate productivity. Rabbit effects were greatest under moderate productivity. Overall effects of kangaroos were benign. Grazing indirectly affected native and exotic plant richness by increasing soil phosphorus and reducing soil health (i.e., nutrient cycling). 4.Synthesis and applications. Our study shows that livestock grazing increases exotic species richness but reduces native richness, while kangaroo grazing increases native richness in environments with low productivity. The results provide clear messages for land managers and policy makers: (1) the coexistence of livestock grazing and plant diversity is only possible within more productive environments and (2) grazing under low or moderate productivity will impact upon native and exotic plant richness.1. 家养牲畜放牧是全球分布最广泛的土地利用方式之一，尤其多见于放牧地（rangelands），该类区域常与野生草食动物放牧活动共存。放牧对植物多样性的影响，大概率取决于放牧强度、草食动物类型、与植物的协同演化关系以及当前的环境条件。 2. 本研究收集了气候、植物生产力、土壤属性、放牧强度以及草食动物类型相关数据，并针对澳大利亚东部451个分布于0.4百万平方公里半干旱放牧地内的样点，测定了上述因素对植物物种丰富度的影响。本研究采用结构方程模型（structural equation modelling），分析了不同草食动物（牛、绵羊、袋鼠、野兔）放牧强度提升对所有样点以及三类沿生产力梯度分布的林地群落子集内本土与外来植物物种丰富度的直接与间接影响。 3. 所有草食动物的放牧直接效应在低生产力环境下最强，且随生产力提升逐渐减弱。近期与历史家畜放牧强度的提升，在低生产力环境下对应更高的外来植物物种丰富度，而在低与中等生产力环境下均对应更低的本土植物物种丰富度。野兔放牧的效应在中等生产力环境下最为显著。总体而言，袋鼠放牧的影响呈良性。放牧可通过提升土壤磷含量与降低土壤健康水平（即养分循环），间接影响本土与外来植物物种丰富度。 4. 综合与应用。本研究表明，家畜放牧会提升外来植物物种丰富度，同时降低本土植物物种丰富度，而袋鼠放牧在低生产力环境下可提升本土植物物种丰富度。本研究结果可为土地管理者与政策制定者提供明确启示：(1) 家畜放牧与植物多样性共存仅能在生产力更高的环境中实现；(2) 低或中等生产力环境下的放牧活动，会对本土与外来植物物种丰富度产生影响。