Abstract

The restoration of forest structure and function is increasingly being used in boreal forests in order to halt the loss of biodiversity. Often ecological restoration is aimed at increasing the volume of dead and dying trees to enhance the biodiversity of deadwood-dependent organisms, but it may also increase population sizes of pest bark beetle species, even several years following restoration. Herein, we used a large-scale restoration experiment in Northern Sweden to assess the 5 years post-restoration effects of restorative gap cutting and prescribed burning on the populations of a set of economically harmful pest bark beetles (Ips typographus, Polygraphus poligraphus, Tomicus piniperda and Pityogenes chalcographus) and the most important predators of bark beetles, Thanasimus spp. In addition, we assessed the effects of forest stand characteristics at stand and landscape scale on the abundance of I. typographus. Five years post-restoration, gap-cut stands supported the highest abundances of P. poligraphus and contained the highest count of spruce trees newly attacked by bark beetles. By contrast, prescribed burning generally sustained the lowest abundances of pest bark beetles, especially I. typographus and P. poligraphus, and the highest abundance of their natural predators Thanasimus spp. The population abundance of I. typographus was also positively affected by the area of clear cuts within a 500 m radius from the stand. In conclusion, prescribed burning appears to be a safer method for ecological restoration than gap cutting in the long-term. According to our results, a risk of a local bark beetle outbreak still remains 5 years following the initiation of ecological restoration treatments on spruce-dominated mature gap-cut stands.

中文翻译：

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用于生物多样性保护的生态恢复引发树皮甲虫害虫及其天敌

摘要

为了阻止生物多样性的丧失，在北方森林中越来越多地使用恢复森林结构和功能的方法。生态恢复通常旨在增加死树和垂死树木的数量，以增强依赖枯木的生物的生物多样性，但它甚至可能在恢复数年后增加害虫树皮甲虫物种的种群规模。本文中，我们在瑞典北部进行了一次大规模的修复实验，评估了修复间隙切割和处方烧伤对一组经济上有害的害虫树皮甲虫（Ips typographus，Polygraphus poligraphus，Tomicus piniperda和Pityogenes chalcographus）和树皮甲虫最重要的捕食者，Thanasimus spp。另外，我们评估了林分特征在林分和景观尺度上对I. typographus丰度的影响。恢复五年后，砍伐的林分支持了最高的P. poligraphus丰产，并且拥有数量最高的新近被树皮甲虫袭击的云杉树木。相反，规定的燃烧通常使害虫树皮甲虫，尤其是I. typographus和P. poligraphus的丰度最低，而其自然捕食者Thanasimus spp的丰度最高。I.Typographus的人口数量展位半径500 m以内的净切面积也对展位产生积极影响。总之，从长远来看，处方燃烧似乎是一种比间隙切割更安全的生态恢复方法。根据我们的结果，在以云杉为主的成熟裂隙林开始生态修复治疗后的5年内，当地树皮甲虫暴发的风险仍然存在。