Spruce-dominated forests are commonly exposed to disturbances associated with mass occurrences of bark beetles. The dieback of trees triggers many physical and chemical processes in the ecosystem resulting in rapid changes in the vegetation of the lower forest layers. We aimed to determine the response of non-tree understory vegetation to the mass dieback of Norway spruce () in the first years after the disturbance caused by the European spruce bark beetle () outbreak. Our study area was the Białowieża Biosphere Reserve covering the Polish part of the emblematic Białowieża Forest, in total 597 ​km. The main data source comprised 3,900 phytosociological relevés (combined spring and summer campaigns) collected from 1,300 systematically distributed forest sites in 2016–2018 – the peak years of the bark beetle outbreak. We found that the understory responded immediately to mass spruce dieback, with the most pronounced changes observed in the year of the disturbance and the subsequent year. Shade-tolerant forest species declined in the initial years following the mass spruce dieback, while hemicryptophytes, therophytes, light-demanding species associated with non-forest semi-natural communities, as well as water-demanding forest species, expanded. , the most common understory species in the Białowieża Forest, showed a distinct fluctuation pattern, with strong short-term expansion right after spruce dieback, followed by a gradual decline over the next 3–4 years to a cover level 5 percentage points lower than before the disturbance. Thus, our study revealed that mass spruce dieback selectively affects individual herb species, and their responses can be directional and non-directional (fluctuation). Furthermore, we demonstrated that the mass dieback of spruce temporarily increases plant species diversity (-diversity).

中文翻译：

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欧洲低地温带森林林下植被对挪威云杉大规模枯死的早期反应

以云杉为主的森林经常受到与树皮甲虫大量出现相关的干扰。树木的枯死会引发生态系统中的许多物理和化学过程，导致较低森林层的植被发生快速变化。我们的目的是确定在欧洲云杉树皮甲虫 () 爆发造成干扰后的最初几年内，非树木林下植被对挪威云杉 () 大规模枯死的反应。我们的研究区域是比亚沃维扎生物圈保护区，覆盖标志性比亚沃维扎森林的波兰部分，总面积 597 公里。主要数据来源包括 2016 年至 2018 年（树皮甲虫爆发的高峰年）从 1,300 个系统分布的森林地点收集的 3,900 个植物社会学相关数据（春季和夏季综合活动）。我们发现，林下植被对大量云杉枯死立即做出反应，在干扰年份和随后的一年观察到最明显的变化。在大规模云杉枯死之后的最初几年，耐荫森林物种减少，而半隐植物、日生植物、与非森林半自然群落相关的需光物种以及需水森林物种则扩大。比亚沃维耶扎森林中最常见的林下树种，表现出明显的波动模式，云杉枯死后短期内扩张强劲，随后在未来 3-4 年内逐渐下降，覆盖水平较之前下降 5 个百分点的干扰。因此，我们的研究表明，大量云杉枯死选择性地影响单个草本物种，并且它们的反应可以是定向的和非定向的（波动）。此外，我们证明云杉的大规模枯死会暂时增加植物物种多样性（-多样性）。