Soil carbon and biodiversity response to Scottish Highlands rewilding

通过恢复生物多样性栖息地和增加生态系统规模的碳(C)储存的潜力，重新野生化越来越被认为是限制生物多样性持续下降和减缓气候变化的有力工具。在苏格兰，大约700万只羊和100万只鹿在没有捕食者的土地上吃草，阻止树木的自然再生，通过栅栏移走这些大型草食动物，在几个小规模的实验中允许了天然森林的再生(见下文)。这些举措在视觉上的成功受到了野生动物保护运动的欢迎，并引发了越来越多的呼声，要求将苏格兰高地重新野生。重新保护倡议通常推断将有更广泛的整体利益(例如，华纳等人)。然而，由于缺乏地上和地下的数据，人们对退耕还林的真正好处，特别是生物多样性的恢复和碳封存的信心有限。虽然这些退耕计划可能通过允许树木生长来增加地面碳储量，但生态系统碳储量的整体变化也取决于陆地生态系统中最大的碳储量：土壤碳储量的反应。苏格兰高地植树试验的最新发现表明，虽然植树导致了地上碳的积累，但同时也导致了地下碳固存的减少(Friggen等人。Ben Lawers自然保护区重新开垦的初步数据表明，土壤碳的减少也可能发生在树木的自然再生之后。此外，土壤是全球最大的生物多样性储藏库，拥有地球总生物多样性的25%以上(Bardgett和van der Putten(2014))。因此，退耕还林对生物多样性的整体效益在很大程度上取决于土壤的反应。因此，迫切需要仔细考虑土壤对退耕还林的反应。一旦考虑土壤，退耕还林能否增加生态系统规模的碳储量和生物多样性？

Rewilding is increasingly considered as a powerful tool to limit both the ongoing declinesin biodiversity and mitigate climate change, through its potential to restore biodiversehabitats and increase ecosystem-scale carbon (C) storage. In Scotland, where ca. sevenmillion sheep and one million deer graze the land predator-free and prevent the naturalregeneration of trees, the removal of these large herbivores through fencing has allowednatural forest regeneration in several small-scale experiments (see below). The visualsuccess of these initiatives has been embraced by the rewilding conservation movementand has led to increasingly vocal calls to 'rewild' the Scottish Highlands. Rewildinginitiatives often infer that there will be wider holistic benefits (e.g., Warner et al. 2021),however, confidence in the true benefits of rewilding, particularly biodiversity recoveryand C sequestration, is limited due to a lack of above and belowground data.While these rewilding initiatives likely increase above ground carbon storage by allowingtree growth, the overall change in ecosystem C storage also depends on the response ofthe largest C stock in terrestrial ecosystems: the soil C stock. Recent findings fromexperimental tree planting in the Scottish uplands suggests that while tree planting led toan accumulation of C aboveground, it simultaneously led to decrease in C sequestrationbelowground (Friggens et al. 2020), thereby cancelling out the aboveground benefits.Preliminary data from a rewilding initiative at Ben Lawers Nature reserve suggest that thisdecrease in soil C may also occur following the natural regeneration of trees.Furthermore, soils are globally the largest reservoir of biodiversity, hosting more than25% of the Planet's total biodiversity (Bardgett and van der Putten (2014). Holisticbenefits of rewilding on biodiversity thus largely depend on the response of the soil.There is thus an urgent need to carefully considering the response of the soil to rewilding.Can rewilding the Scottish Highlands increase ecosystem-scale carbon storage andbiodiversity, once the soil is considered?