Restoring forests has recently received considerable attention in the context of sequestering carbon and supporting biodiversity. Although considering alien species as a tool for natural forest restoration still remains controversial, harnessing alien species when they are already present in an ecosystem might result in overall benefits for nature and society. In this study we evaluated whether the presence of an alien tree species supports or hinders the establishment of naturally regenerating forests in Shiretoko National Park, Japan. In particular, we focused on Larix kaempferi, which is widely present yet non-native to the region, and examined how this alien species affects two factors influencing the success of restoration: wind disturbance and deer herbivory. We examined the following effects of L. kaempferi plantations on natural regeneration: (1) the windbreak function for protecting native tree growth and (2) the nursery function to promote the regeneration of native tree saplings and seedlings under high herbivory pressure. We assessed tree height and regeneration, using large-scale remotely sensed data and terrestrial inventory data in five major vegetation types. We found that L. kaempferi plantations can protect native species from predominant winds. Additionally, L. kaempferi canopy cover promoted abundance and species richness in understory saplings and seedlings compared to other vegetation types such as primary and secondary forests, even under excessive browsing pressure. No regenerating L. kaempferi individuals were observed during the field census, suggesting the species is likely not invasive in our study system. The positive relationship between alien tree species and the regeneration of native tree assemblages emphasizes that existing alien species have the potential to act as nurse plants. Our findings imply that the presence of alien species can contribute to natural forest restoration by improving the local environmental conditions for native species in the short-term. Given the multiple ecological and social needs in our changing world, careful consideration is required to evaluate the long-term consequences of alien species. Especially in ecosystems in which alien species have already established, using their positive functions rather than swiftly eradicating them from the landscape might be beneficial for long-term restoration goals. We conclude that managers need to be aware of the context-dependency of alien species to make restoration more effective.

最近，在固碳和支持生物多样性的背景下，恢复森林受到了相当大的关注。尽管将外来物种作为恢复自然森林的工具仍然存在争议，但是在外来物种已经存在于生态系统中时加以利用可能会为自然和社会带来总体利益。在这项研究中，我们评估了外来树种的存在是否支持或阻碍了日本知床国家公园内自然再生森林的建立。尤其是，我们集中研究了该地区广泛存在但非本地的落叶松（larix kaempferi），并研究了该外来物种如何影响影响恢复成功的两个因素：风扰和鹿食草。我们研究了以下影响L. kaempferi人工林的自然更新：（1）防风功能可保护原生树的生长，（2）苗圃功能可在高食草压力下促进原生树苗和幼苗的再生。我们使用五种主要植被类型的大规模遥感数据和地面清单数据，评估了树木的高度和更新。我们发现L. kaempferi人工林可以保护本地物种免受主要风的侵害。此外，即使在浏览压力过大的情况下，与其他植被类型（例如原始森林和次要森林）相比，kaempferi L. kaempferi的树冠覆盖也促进了林下树苗和幼苗的丰度和物种丰富性。没有再生的L. kaempferi在野外普查期间观察到个体，表明该物种在我们的研究系统中可能不是侵入性的。外来树种与原生树种再生之间的正相关关系强调，现有外来树种具有充当苗木的潜力。我们的发现表明，外来物种的存在可以通过改善短期内当地物种的当地环境条件来促进天然林的恢复。考虑到我们不断变化的世界中多重的生态和社会需求，需要仔细考虑以评估外来物种的长期后果。特别是在已经建立了外来物种的生态系统中，使用它们的积极功能，而不是从景观中迅速消除它们，可能对长期恢复目标有利。我们得出的结论是，管理者需要意识到外来物种的背景依赖性，以使恢复工作更加有效。