Grassland nature reserves safeguard a high species richness and biomass of grasshoppers

In the course of land-use change, especially since the mid-20th century,
the area of semi-natural (unimproved) grasslands has dramatically
decreased. One way to counteract this process is to designate nature
reserves. However, the effectiveness of nature reserves is controversial.
The aim of our study was to evaluate the environmental drivers of species
richness and biomass of Orthoptera (hereinafter termed ‘grasshoppers’) in
grasslands inside nature reserves and within the intensively-used
agriculture landscape (hereinafter termed ‘wider countryside’). For this
purpose, we sampled the grasshoppers at the landscape scale in 45 randomly
selected plots. Each plot had a size of 5 ha. The abundance of
grasshoppers, as a basis for the biomass calculation, was recorded at the
habitat scale in 20 meadow patches (500 m² each). In addition, various
environmental parameters such as habitat diversity, mowing intensity and
vegetation structure were determined at the landscape and habitat scale.
Our results illustrate the importance of nature reserves for the
conservation of grasshoppers. Control plots in the wider countryside
harboured fewer species than plots within nature reserves. The differences
were even clearer among threatened species. On average, plots in nature
reserves had almost twice as many threatened species than control plots in
the wider countryside. The comparison revealed similar patterns at the
habitat scale: both the number of species and biomass were higher in
nature reserves. At the landscape scale, number of species were best
explained by the amount of wet grassland and habitat diversity. We
identified mowing intensity and to a lower extend the degree of drainage
as the key drivers of species richness and biomass at the habitat scale.
Synthesis and applications: To preserve biodiversity in nature reserves,
we recommend (i) leaving uncut refuges during mowing and (ii) blocking
drainage to stabilize the water level. Both measures contribute to a high
species number and abundance of grasshoppers and many other insects. An
effective conservation measure to promote species richness in the wider
countryside would be to increase habitat diversity. This can be done by
creating or restoring fallow islands, field margins, fringes and
hedgerows.

在土地利用变化进程中，尤其是20世纪中期以来，半自然（未改良）草地的面积已大幅缩减。划定自然保护区（nature reserves）是抵消这一趋势的途径之一，但其保护效果尚存争议。本研究旨在评估自然保护区内及集约化农业景观（intensively-used agriculture landscape，以下简称“外围乡村区域”（wider countryside））中直翅目（Orthoptera，以下简称“蝗虫”）的物种丰富度与生物量的环境驱动因子。为此，我们在景观尺度下对45个随机选取的样地（plot）开展蝗虫采样，每个样地面积为5公顷（ha）。以蝗虫种群丰度作为生物量计算的基础，我们在20个单块面积为500平方米的草地斑块的生境尺度下记录了其种群丰度。此外，我们还在景观与生境尺度下测定了多项环境参数，包括生境多样性、刈割强度与植被结构。研究结果证实了自然保护区在蝗虫保护中的重要价值。外围乡村区域的对照样地的物种数量低于自然保护区内的样地，该差异在受威胁物种（threatened species）中更为显著。平均而言，自然保护区内样地的受威胁物种数量几乎是外围乡村区域对照样地的两倍。生境尺度下的对比亦呈现相似规律：自然保护区内的物种数量与生物量均更高。在景观尺度下，物种丰富度的变化可由湿地草地面积与生境多样性得到最佳解释。我们还发现，刈割强度以及相对次要的排水程度是生境尺度下物种丰富度与生物量的关键驱动因子。综合与应用：为保护自然保护区内的生物多样性，我们提出两项建议：（i）在刈割作业时保留未割的庇护斑块；（ii）堵塞排水设施以稳定水位。这两项措施均有助于提升蝗虫及其他众多昆虫的物种数量与种群丰度。在外围乡村区域提升物种丰富度的有效保护措施，是增加生境多样性。这可通过创建或恢复休耕岛、田埂、边缘带与绿篱（hedgerows）来实现。