Saikkonen Kari, Saikkonen Otto, Helander Marjo, Saloniemi Irma
Kevo Subarctic Research Institute, Biodiversity Unit, University of Turku, 20014, Turku, Finland.
Department of Forest Sciences, University of Helsinki, 00014, Helsinki, Finland.
Sci Rep. 2025 Jan 28;15(1):3597. doi: 10.1038/s41598-025-87478-7.
Alpine and Arctic treelines are assumed to be shifting toward higher latitudes and altitudes as a consequence of climate warming. Here, we compared the survival and growth of 1264 silver birch (Betula pendula Roth.) trees representing nine half-sib families. The trees were planted in two arboreta situated in distinct altitudinal environments in northern Finland in 1976 and 1977. The arboreta were located 9 km from each other and approximately 60 km north from the species' most northern natural growth site at that time. They were fenced to prevent vertebrate grazing, which is known to be among the most important factors limiting the expansion and regeneration of forests in European treeline ecotones. Overall, 90% and 81% of the trees were alive five and 40 years after planting in the two arboreta, respectively. Survival of trees varied among the half-sib families, especially in Arboretum 1, situated in a lower altitudinal environment characterized by soils with lower levels of nutrients, a longer growing season, and harsher winter temperatures. Trees were distinctively bigger in Arboretum 2: 50% taller (6.2 m vs. 4.4 m) and 68% thicker (9.5 cm vs. 5.6 cm) compared to trees in Arboretum 1. Furthermore, the performance of half-sib families varied depending on the garden they were grown in. These results demonstrate that the acclimation capacity of B. pendula allows its distribution to expand north from the present range; however, local abiotic environmental conditions (soil fertility and winter temperatures) and other selection pressures (herbivory) are likely to affect the genetic structure and growth of B. pendula populations.
由于气候变暖，高山和北极树线被认为正在向更高的纬度和海拔移动。在此，我们比较了代表9个半同胞家系的1264棵银桦（Betula pendula Roth.）树的存活和生长情况。这些树于1976年和1977年种植在芬兰北部两个处于不同海拔环境的树木园里。这两个树木园相距9公里，距离当时该物种最北的自然生长地以北约60公里。它们被围栏围住以防止脊椎动物啃食，已知这是限制欧洲树线交错带森林扩张和更新的最重要因素之一。总体而言，在两个树木园中，种植后5年和40年分别有90%和81%的树存活。树的存活情况在半同胞家系间有所不同，尤其是在树木园1中，该树木园处于较低海拔环境，其土壤养分含量较低、生长季较长且冬季温度更严酷。树木园2中的树明显更大：与树木园1中的树相比，高50%（6.2米对4.4米），粗68%（9.5厘米对5.6厘米）。此外，半同胞家系的表现因种植所在的树木园而异。这些结果表明，垂枝桦的适应能力使其分布范围能够从当前区域向北扩展；然而，当地的非生物环境条件（土壤肥力和冬季温度）以及其他选择压力（食草作用）可能会影响垂枝桦种群的遗传结构和生长。
