Abstract A major problem within forestry is winter browsing on young Scots pine (Pinus sylvestris) by European moose (Alces alces). Moose are selective foragers and make foraging decisions on many scales, for example, they avoid trees with high levels of plant defensive compounds, which reduce digestibility. Bark extract from Norway spruce (Picea abies) is known to have high levels of such defensive compounds. The aim of this study was to evaluate the effects of Norway spruce bark extract as a repellent to European moose. Spruce bark was extracted in a conventional way with ethanol as the solvent, creating a solution that was applied to the apical leader of young pine trees in planted forests. In two field trials in northern Sweden (winter 2017–2018 and winter 2018–2019), the apical leader of young pine trees (height 1–2.5 m) were sprayed with bark extract from Norway spruce. A total of 5247 pine trees were included in the study. The field trials showed that spruce bark extract lowered the number of browsed apical leader of pine trees, and directed moose to browse less valuable lateral shoots, and neighboring trees. During the first field trial, apical leaders were treated every second meter along transects with a concentration of the spruce bark extract of 2.8% by dry weight. The level of browsed apical leaders changed from 15.1% to 6.8% of all apical leaders. During the second field trial, apical leaders were treated in circular plots, in which all main stems inside the circle were treated with a concentration of the spruce bark extract of 5.0% by dry weight. The level of browsed apical leaders changed from 19.5% to 4.7% of all apical leaders. Hence, results show that spruce bark extract (a non-toxic forest byproduct) can function as an efficient repellent. The bark extract can control browsing to a level that is considered acceptable – generally a maximum of 5% of all apical leaders browsed every year. This would result in approximately 7 out of 10 trees, in treated small scale areas, having unbrowsed apical leaders when the trees reach a height at which the apical leaders are safe from moose browsing.

中文翻译：

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天然驱虫剂，可保护苏格兰松树 Pinus sylvestris 免受欧洲驼鹿 Alces alces 的侵害

摘要 林业中的一个主要问题是欧洲驼鹿 (Alces alces) 对年轻的苏格兰松 (Pinus sylvestris) 进行冬季觅食。驼鹿是有选择性的觅食者，并在许多尺度上做出觅食决定，例如，它们避开具有高水平植物防御化合物的树木，这会降低消化率。已知来自挪威云杉 (Picea abies) 的树皮提取物具有高水平的此类防御化合物。本研究的目的是评估挪威云杉树皮提取物作为欧洲驼鹿驱虫剂的效果。以乙醇为溶剂，以传统方式提取云杉树皮，制成一种溶液，应用于人工林中松树幼树的顶端。在瑞典北部的两次田间试验（2017-2018 年冬季和 2018-2019 年冬季）中，幼松树的顶端领导者（高度 1-2. 5 m) 用来自挪威云杉的树皮提取物喷洒。该研究共包括 5247 棵松树。田间试验表明，云杉树皮提取物降低了松树顶端被啃食的数量，并引导驼鹿啃食价值较低的侧枝和邻近树木。在第一次田间试验期间，沿横断面每隔一米用浓度为 2.8%（干重）的云杉树皮提取物处理顶端的引线。浏览的顶端领导的​​水平从所有顶端领导的​​ 15.1% 变为 6.8%。在第二次田间试验期间，在圆形地块中处理顶端的领导者，其中圆形内的所有主茎都用浓度为 5.0% 干重的云杉树皮提取物处理。浏览的顶端领导的​​水平从所有顶端领导的​​ 19.5% 变为 4.7%。因此，结果表明，云杉树皮提取物（一种无毒的森林副产品）可以作为一种有效的驱虫剂。树皮提取物可以将浏览控制在一个被认为可以接受的水平——通常每年浏览的所有顶端领导者最多为 5%。这将导致在经过处理的小规模区域中，大约十分之七的树木在树木达到顶端顶端不会被驼鹿啃食的高度时具有未浏览的顶端顶端。