Abstract

The native bracken fern (Pteridium aquilinum (L.) Kuhn) has become increasingly invasive in abandoned or undergrazed Alpine grasslands. Bracken stands are generally assumed to be poor in species, but there is still very little information about the impact on the fauna. We recorded Orthoptera communities of 24 sample plots with varying bracken cover. Compared to plots with only sparse or medium bracken cover, species richness was highly significantly lower in densely overgrown plots, while the former two did not differ markedly. Multivariate ordination analyses revealed gradients with unequal orthopteran communities, showing distinct patterns of bracken cover clustering. Based on indicator values, 13 of 23 Orthoptera species turned out to be significantly or marginally significantly associated with a single bracken cover stratum or a combination of two strata, whereby all nine Red List species were primarily restricted to sparse or medium bracken cover. However, some generalist species were found to favor denser bracken stands, such as Tettigonia viridissima, contributing to the local Orthoptera beta diversity. Our data suggest that ongoing rotational sheep grazing with temporary paddocks is regarded as the most preferable management system. However, selected parts of the study area, which have only sparse vegetation and no pressure of bracken or scrub overgrowth, are recommended to be alternately left ungrazed for a few years to allow for the coexistence of different successional stages. Low-intensity bracken control measures, situationally by mowing or uprooting, are considered appropriate and should be pursued.

Implications for insect conservation

Even though most specialized and rare Orthoptera species in Western Europe tend to prefer sparsely vegetated areas, subareas with medium to even dense vegetation cover might promote certain generalist species, leading to a higher local species richness.

中文翻译：

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蕨菜（Pteridium aquilinum (L.) Kuhn）在干燥的高山草原上过度生长阻碍了红名单直翅目，但支持当地直翅目β多样性

摘要

原生蕨菜 ( Pteridium aquilinum)(L.) Kuhn) 在废弃或未充分放牧的高山草原中变得越来越具有侵入性。人们普遍认为蕨菜林的物种很少，但关于对动物群的影响的信息仍然很少。我们记录了具有不同蕨类植物覆盖的 24 个样本地块的直翅目群落。与只有稀疏或中等蕨菜覆盖的地块相比，茂密的杂草地块的物种丰富度显着降低，而前两者没有显着差异。多变量排序分析揭示了不等的直翅目群落的梯度，显示出蕨菜覆盖聚类的不同模式。根据指标值，23 种直翅目物种中有 13 种与单个蕨菜覆盖层或两个层的组合显着或轻微显着相关，因此，所有九种红色名录物种主要限于稀疏或中等蕨类植物覆盖。然而，发现一些通才物种更喜欢密集的蕨类植物，例如Tettigonia viridissima，有助于当地直翅目β 多样性。我们的数据表明，在临时围场内持续轮作放牧被认为是最可取的管理系统。然而，研究区的选定部分，只有稀疏植被，没有蕨类植物或灌木丛过度生长的压力，建议交替放牧几年，以便不同演替阶段共存。低强度的蕨菜控制措施，根据情况通过割草或连根拔起，被认为是合适的，应该继续实施。

对昆虫保护的影响

尽管西欧大多数特化和稀有直翅目物种往往更喜欢植被稀疏的地区，但中等至密集植被覆盖的分区可能会促进某些通才物种，从而导致更高的当地物种丰富度。