Data from: Response of mountain Picea abies forests to stand-replacing bark beetle outbreaks: neighborhood effects lead to self-replacement

1. Large, severe disturbances drive many forest ecosystems over the long term, but pose management uncertainties when human experience with them is limited. Recent continent-scale outbreaks of bark beetles across the temperate Northern Hemisphere have raised major concerns as to whether coniferous forests will regenerate back toward pre-outbreak condition and meet possible reforestation objectives. To date, however, analyses of post-outbreak regeneration across broad spatial and temporal scales have been rare, and entirely lacking for many regions. 2. Following a series of large, severe (~99% overstory mortality) outbreaks of spruce bark beetles Ips typographus in Central Europe, we capitalized on an extensive forest inventory data set (n=615 plots across ~7000 ha) to evaluate regeneration dynamics in Norway spruce Picea abies forests across the Bohemian Forest Ecosystem (spanning Germany and the Czech Republic). We asked whether neighbourhood effects (conspecific advance regeneration of spruce) would support prompt regeneration back to spruce forest, or if the rapid, severe canopy mortality would overwhelm this influence and promote pioneer and broadleaf species. We tracked 15 years of post-outbreak regeneration dynamics (occupancy, density, height, composition) of all tree species and evaluated initial variations in successional pathway and structure. 3. Median tree regeneration density increased from ~400 trees ha−1 at the time of outbreak to ~2000 trees ha−1 within a decade, and occupancy increased from 58% to 76%. The increases were driven by spruce, which primarily recruited from advance regeneration, gradually occupying greater height classes. Only one broadleaf/pioneer species increased in relative proportion, for a brief (<3-year) period before declining again. Nevertheless, both pure spruce and spruce-broadleaf stands were common and, coupled with wide variations in density and height, contributed to diverse early-successional structure. 4. Synthesis and applications. Contrary to common expectations, spruce beetle outbreaks in Central Europe effectively promoted their host in the long-term. Outbreak-affected forests are naturally self-replacing even after severe canopy mortality, when positive neighbourhood effects of conspecific advance regeneration lead to rapid replacement of the dominant species. Thus, natural regeneration may be considered among the most effective ways to meet possible reforestation objectives in forests destroyed by beetles.

1. 长期以来，大规模重度干扰驱动着诸多森林生态系统的演替，但当人类对这类干扰的应对经验不足时，便会带来管理层面的不确定性。近期，温带北半球范围内出现了大陆尺度的树皮甲虫（bark beetles）暴发疫情，引发了学界的广泛担忧：针叶林（coniferous forests）能否恢复至虫害暴发前的林分状态，并达成既定造林目标？然而迄今为止，针对跨空间和时间尺度的虫害后森林更新的研究仍较为匮乏，许多地区甚至完全没有相关分析。
2. 在中欧地区发生的一系列大规模重度云杉八齿小蠹（Ips typographus）虫害暴发（冠层死亡率约达99%）后，本研究依托覆盖约7000公顷、包含615块样地的大规模森林清查数据集（forest inventory data set），对横跨德国与捷克共和国的波希米亚森林生态系统（Bohemian Forest Ecosystem）内的挪威云杉（Picea abies）林更新动态展开评估。本研究旨在探讨两个核心问题：一是云杉的同种先期更新苗（conspecific advance regeneration）所带来的邻域效应能否助力林分快速恢复为云杉纯林；二是快速且重度的冠层死亡是否会抵消这一效应，进而促进先锋物种（pioneer species）与阔叶树种的定植。研究团队追踪了虫害暴发后15年间所有树种的更新动态（包括占有率、密度、树高与群落组成），并分析了演替路径（successional pathway）与林分结构的初始变异。
3. 林分更新密度的中位数从虫害暴发时的约400株·公顷⁻¹提升至十年内的约2000株·公顷⁻¹，有更新发生的样地占有率也从58%升至76%。这一增长主要由云杉驱动，其更新株主要源自先期更新苗，并逐渐占据更高的树高层级。仅有一种阔叶/先锋物种的相对占比曾出现短暂上升（持续时长不足3年），随后便再度回落。尽管如此，云杉纯林与云杉-阔叶混交林均较为常见，加之林分密度与树高存在广泛差异，共同塑造了多样的早期演替林分结构。
4. 研究结论与应用启示：与普遍认知相悖的是，中欧地区的云杉小蠹虫害暴发在长期尺度上实则促进了其宿主树种的存续。即便经历了重度冠层死亡，受虫害影响的森林仍可通过自然过程实现自我更新：当云杉的同种先期更新苗带来正向邻域效应时，林分可快速完成优势树种的更替。因此，自然更新可被视为受甲虫破坏的森林达成造林目标的最有效途径之一。