Table_1_Maintaining the protective function of mountain forests under climate change by the concept of naturalness in tree species composition.XLSX

In Swiss mountain areas, the protective function of forests is the predominant ecosystem service having high cultural and economic significance. It is assumed that natural forests or close-to-natural forests, i.e., forests being in the equilibrium with environmental conditions are the most resilient and resistant in regard to disturbances and hence best protecting people and assets on the long run. Here, we estimated the naturalness of the tree species composition by comparing Swiss National Forest Inventory (NFI) data with current and future potential Natural forest Site Types (NST). Based on this analysis, we identified species that are under or over-represented in protective mountain forests and derived the subsequent potential for management interventions. The urgency of management interventions is expected be small if all predominant tree species of the idealized potential natural forests are present and only their relative portions in the stand need adjustment. In contrast, interventions are advisable, if predominant tree species of the current and future potential natural forests are absent. Based on NFI data, the tree species composition of 47% of the protective mountain forests were classified as “natural” or “close-to-natural,” while the remaining 53% were classified as “not natural” or “partly natural.” Norway spruce [Picea abies (L.) H. Karst.] and European larch (Larix decidua Mill.) were the two most over-represented species under current and even more so under predicted future climatic conditions. To date, silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) were the two species most frequently absent in protective mountain forests, in which they should prevail. Apart from European beech, the most prominent increase in prevalence is predicted for oak (sessile oak and pubescent oak; Quercus petrea Liebl., Q. pubescens Willd.) and small-leaved lime (Tilia cordata Mill.). These species were currently missing from more than 75% of the stands, in which they are expected to be dominant under future conditions. Our analysis indicates the need to transform tree species compositions of protective mountain forests to optimize fitness under future climates. Some of these transformations will take place naturally, incited by disturbances, others—the majority of them—will need active management interventions.

在瑞士山地林区，森林防护功能是兼具极高文化与经济价值的核心生态系统服务。
学界普遍认为，天然林（natural forest）或近天然林（close-to-natural forest）——即与环境条件处于动态平衡的森林——在应对外界干扰时具备最强的抗性与恢复力，因此从长期来看能最有效地保护民众与资产安全。
本研究通过对比瑞士国家森林清查（Swiss National Forest Inventory, NFI）数据与当前及未来潜在天然林立地类型（Natural forest Site Types, NST），评估了林木物种组成的自然性程度。基于此分析，本研究识别出山地防护林中占比不足或过高的树种，并推导了后续经营干预的可行空间。
若理想潜在天然林的优势树种均已存在，仅需调整林分中各树种的相对占比，则经营干预的紧迫性较低；反之，若当前及未来潜在天然林的优势树种缺失，则需开展经营干预。
基于NFI数据，47%的山地防护林的林木物种组成被归类为"天然"或"近天然"状态，剩余53%则被归类为"非天然"或"半天然"状态。挪威云杉[Picea abies (L.) H. Karst.]与欧洲落叶松（Larix decidua Mill.）是当前占比过高的两大树种，在未来预估气候条件下其占比过剩的情况将更为显著。
迄今为止，欧洲银冷杉（Abies alba Mill.）与欧洲山毛榉（Fagus sylvatica L.）是山地防护林中最常见的缺失优势树种，而这两类树种本应在林分中占据主导地位。除欧洲山毛榉外，预估占比增幅最显著的树种为栎属（无梗花栎与柔毛栎；Quercus petrea Liebl.、Q. pubescens Willd.）以及小叶椴（Tilia cordata Mill.）。目前，这些树种在其预估未来将占据主导地位的林分中，缺失率超过75%。
本研究分析表明，需调整山地防护林的林木物种组成，以优化其在未来气候下的适应性。其中部分演替将由干扰事件诱发自然发生，而绝大多数演替则需要通过主动经营干预来推进。