Forest clear-cuts support diverse moth fauna but lack common grassland species

Forests ecosystems sustaining most of the terrestrial biodiversity are under increasing anthropogenic pressure. Both the protection of the remaining natural forests and the mitigation of the negative effects of silviculture are of primary conservation concern. Clear-cut areas are the main open habitats in production forests, potentially offering temporary refuge for species from declining semi-natural grasslands. Although several groups of flower-visiting insects, including butterflies, have been reported to thrive in clear-cuts, a taxonomically comprehensive understanding of the insect fauna utilising these habitats is lacking. In this study, we examined the assemblages of nocturnal macromoths (Lepidoptera: Marcoheterocera) in forest clear-cuts of varying age (2–6 years) and regeneration regimes (natural vs. artificial) in Northern Europe. Using automatic sugar-bait traps, we sampled 50 clear-cuts and three pairs of forest-grassland reference sites over two summers. Nocturnal moths of the clear-cuts were highly diverse, harbouring 50% of the regional species pool of noctuids. However, several common grassland-associated species, as well as a few forest species, were nearly absent. Although the similarity between clear-cut and forest assemblages increased with clear-cut age, the recorded characteristics of the clear-cuts had little overall influence on moth assemblages. Artificially regenerated clear-cuts, characterised by a more open vegetation structure, supported slightly higher moth species richness and diversity compared to naturally regenerating sites.

Policy implications: Our results highlight the role of forest clear-cuts in supporting insect biodiversity. As such, clear-cuts warrant special consideration as a distinct habitat type. However, the effects of clear-cut regeneration and maintenance methods on assemblages of moths appear weaker than in various other insect groups. More importantly, the absence of several common grassland species highlights that clear-cuts cannot fully replace traditional open habitats. This underscores the importance of conserving semi-natural grasslands.

支撑绝大多数陆地生物多样性的森林生态系统，正面临日益加剧的人为活动压力。保护现存天然林，以及缓解营林（silviculture）活动带来的负面影响，均为生物多样性保护的核心议题。皆伐迹地（clear-cut areas）是用材林内的主要开阔生境，可为日渐衰退的半自然草地（semi-natural grasslands）中的物种提供临时庇护场所。尽管已有研究证实，包括蝴蝶在内的多个访花昆虫类群在皆伐迹地中种群繁茂，但目前学界对利用该类生境的昆虫区系仍缺乏分类学维度的全面认知。
本研究针对北欧地区林龄2~6年、更新方式各异（天然更新与人工更新）的森林皆伐迹地，调查了其夜行性大型蛾类（鳞翅目：Marcoheterocera）的群落组成。研究依托两个夏季的野外采样工作，通过自动糖诱陷阱，对50处皆伐迹地与3对林草对照样地进行了样本采集。结果显示，皆伐迹地内的夜行性蛾类多样性极高，其所承载的夜蛾科（noctuids）物种数占区域物种库的50%。但与此同时，多种常见的草地关联物种，以及少量森林特有物种，在皆伐迹地中几乎未见分布。尽管皆伐迹地与原生林的蛾类群落相似性随迹地林龄增长而提升，但整体而言，皆伐迹地的各项特征对蛾类群落的影响较为有限。人工更新的皆伐迹地因植被结构更为开阔，其蛾类物种丰富度与多样性略高于天然更新样地。

政策启示：本研究结果凸显了森林皆伐迹地在支撑昆虫生物多样性方面的关键作用。据此，皆伐迹地作为一类独特的生境类型，应当获得特殊的关注与政策考量。不过，皆伐更新与抚育方式对蛾类群落的影响，似乎弱于其对其他多数昆虫类群的影响。更为重要的是，多种常见草地物种的缺失表明，皆伐迹地无法完全替代传统的开阔生境。这进一步强调了保护半自然草地的必要性与紧迫性。