Retention approaches in forest management are today common in several North European countries, integrated into the clearcutting practice as a way to promote biodiversity and maintain ecosystem functions. Individual green trees and retention patches (tree groups) are retained at final harvest, and deadwood is left at site or created. Here, we review research on retention in Sweden, Finland, Norway, the Baltic States, and NW Russia, with special focus on biodiversity. Following the first publication in 1994, about 180 peer-reviewed articles have been published. We present results from a systematic search of the retention literature, separated into the following topics: buffer zones, retention patches, high stumps, other types of deadwood, European aspen Populus tremula, and cost-efficiency. Russian literature is synthesized separately since studies from this region have so far almost exclusively been published in the Russian language. Furthermore, we describe six ongoing large-scale, replicated experiments with varying retention levels, five in Finland and one in Sweden, and summarize their main results. Among main conclusions for practice from the literature and experiments are that retention patches as large as 0.5 ha and 10-m-wide buffers to watercourses are not enough to maintain pre-harvest species composition but survival of forest species is still larger than on conventional clearcuts. Deadwood on clearcuts may present important habitats to saproxylic species, including rare and red-listed ones and a prioritization of tree species per stand is recommended. We identify several important future research directions including switch of focus towards the landscape as well as the species population level. Surveys in parts of European Russia where retention has been unintentionally implemented already for a century would indicate possible future trajectories of biodiversity and their drivers in other regions of Northern Europe. A stronger link to ecological theory would help in study designs and in the formulation of predicted outcomes.

中文翻译：

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北欧保留林研究

如今，森林管理中的保留方法在北欧一些国家很普遍，已被纳入明确实践中，以促进生物多样性和维持生态系统功能。最终收获时会保留个别的绿树和保留斑块（树组），而枯木则留在原地或创建。在这里，我们回顾了在瑞典，芬兰，挪威，波罗的海国家和俄罗斯西北地区的保留研究，特别关注生物多样性。自1994年首次发表以来，已经发表了约180篇经过同行评审的文章。我们通过对保留文献的系统搜索来提供结果，这些文献分为以下主题：缓冲区，保留斑块，高树桩，其他类型的沉木，欧洲白杨毛木和成本效益。俄语文学是单独合成的，因为到目前为止，该地区的研究几乎只以俄语出版。此外，我们描述了六个正在进行的具有不同保留水平的大规模重复实验，其中五个在芬兰，一个在瑞典，并总结了其主要结果。从文献和实验中得出的主要实践结论是，截留面积最大为0.5公顷且在水道上有10米宽的缓冲带不足以维持捕捞前物种的组成，但是森林物种的存活率仍然比常规的伐木方式更大。 。阔叶树上的沉木可能会为saproxylic物种（包括稀有和列入红色名录的物种）提供重要的栖息地，因此建议对每个林分的树木进行优先排序。我们确定了几个重要的未来研究方向，包括重点转向景观以及物种种群水平。在已经无意实施保留一个世纪的欧洲俄罗斯部分地区进行的调查将表明，北欧其他地区生物多样性及其驱动因素的未来可能轨迹。与生态理论的更紧密联系将有助于研究设计和预测结果的制定。