Experimental rewilding enhances grassland functional composition and pollinator habitat use

1. Semi-natural grasslands are rich in biodiversity and thus important habitats for conservation, yet subjected to rapid declines due to agricultural intensification or abandonment. Promoting a more diverse mammalian herbivore community, including large and megaherbivores, may result in positive cascade effects for biodiversity and ecosystem functioning. Therefore, reintroducing an ecologically functional substitute of an extinct large herbivore could mitigate current biodiversity declines and foster semi-natural grassland conservation. 2. To test this hypothesis, we set up a 3-year rewilding experiment where 12 feral horses were introduced in three 10-hectare enclosure replicates (four horses per enclosure). We used community-weighted mean plant functional traits to elucidate plant community changes induced by grazing through time. We additionally investigated the effects of the experimental treatment on insect pollinated plants and on pollinator habitat use. 3. The grassland community exerted a mixed tolerance/avoidance response to grazing. This resulted in plant functional compositional changes which favoured prostrate plant species with higher specific leaf area, characteristic of ruderal communities. 4. Plant species richness was higher in grazed compared to ungrazed areas. Butterfly and bumblebee habitat use, as well as feeding and resting activities were also higher in grazed areas. Moreover, the number of pollinators increased with plant species richness. 5. Synthesis and applications. This study demonstrates that to enhance the diversity of a given herbivore community with an ecologically functional substitute of extinct wild horses can have significant effects on the functional composition of grasslands, mitigate plant species declines, and boost pollinator habitat use. Thus, rewilding interventions with large herbivores may offset current biodiversity declines by maintaining important functional links between plants and pollinators in grassland ecosystems.

1. 半自然草原（semi-natural grasslands）生物多样性丰富，是至关重要的保护栖息地，却因农业集约化与生境弃耕正经历快速衰退。引入包含大型及巨型草食动物在内的更多元化哺乳动物草食动物群落，或可对生物多样性与生态系统功能产生正向级联效应。因此，重新引入已灭绝大型草食动物的生态功能替代物，有望缓解当前的生物多样性衰退态势，助力半自然草原保护工作。
2. 为验证该假说，我们开展了一项为期3年的再野化实验：将12匹野马（feral horses）投放至3个面积为10公顷的重复围栏样地中，每个围栏放养4匹马。我们通过群落加权平均（community-weighted mean）植物功能性状，解析放牧作用随时间推移对植物群落造成的改变；此外还探究了该实验处理对虫媒植物（insect pollinated plants）以及传粉者（pollinator）栖息地利用的影响。
3. 草原群落对放牧表现出混合的耐受/回避响应，由此引发的植物功能组成变化，更青睐具备更高比叶面积（specific leaf area）的匍匐植物物种——这是杂草群落（ruderal communities）的典型特征。
4. 放牧样地的植物物种丰富度显著高于未放牧对照样地。蝴蝶与熊蜂（bumblebee）的栖息地利用情况，以及其取食、休憩活动频次，在放牧样地中同样更高。此外，传粉者数量随植物物种丰富度的提升而显著增加。
5. 综合与应用。本研究证实，利用已灭绝野生马的生态功能替代物来提升草食动物群落多样性，可显著改变草原的功能组成，缓解植物物种衰退，并提升传粉者的栖息地利用效率。因此，引入大型草食动物的再野化干预措施，可通过维持草原生态系统中植物与传粉者之间的关键功能联系，抵消当前的生物多样性衰退趋势。