Land-use intensity mediated effects of microclimate on insect diversity
Grasslands rank among the most species-rich habitats of Central Europe supporting a remarkable diversity of insect communities. However, land-use intensification poses a well-documented threat to these communities. When applied intensively, management practices such as fertilisation, mowing, and grazing can reduce plant diversity, homogenise habitat structure, deplete the resources and shelter insects depend on, and cause direct mortality. Further, land use fundamentally shapes the microclimatic conditions insects experience at very small spatial scales, an indirect pathway that remains poorly understood. Extensively managed grasslands are characterised by heterogenous vegetation structures, providing a broad variation of microclimatic niche spaces with temperature differences of up to 20°C co-occurring across just a few metres. This diversity of microclimatic niches represents a critical component of habitat quality, potentially supporting high local diversity through thermal niche partitioning and the provision of small-scale refugia. In contrast, intensively managed grasslands are expected to offer a narrower and temporally less stable range of microclimatic conditions. Whether differences in microclimatic niche space systematically mediate the relationship between land-use intensity and insect diversity has, to our knowledge, not previously been tested across sites spanning a broad gradient of land-use intensity.
We aim to understand how microclimate mediates the effects of land-use intensity on insect diversity. Working across all 150 grassland Experimental Plots of the Biodiversity Exploratories, we will: (i) assess insect diversity and community composition using standardised suction sampling to derive species abundance data, from which species-specific microclimatic niches will be calculated; (ii) characterise land surface temperature at centimetre-scale spatial resolution using UAV-borne thermal infrared cameras as well as stationary thermal cameras and temperature sensors; (iii) develop predictive models to estimate the air temperatures perceived by insects within the grassland canopy from UAV-derived surface temperatures and structural plant traits; (iv) measure critical thermal maxima (CTmax) of selected insect species to assess how thermal tolerance relates to land-use intensity and local microclimate; and (v) integrate all data streams to disentangle the direct and microclimate-mediated effects of land-use intensity on insect communities.
We hypothesise that, compared to intensively managed grasslands, extensively managed, structurally heterogeneous grasslands provide broader microclimatic niche space, resulting in higher insect species richness. Further, we expect insect species to differ in their microclimatic niches, such that these differences contribute to explaining species-specific occurrence and abundance patterns. Regarding the individual land-use components, we expect that frequent mowing abruptly destabilises microclimatic conditions by shifting previously cooler areas to warmer conditions, reducing the temporal stability of microclimatic niche space, and that fertilisation narrows microclimatic niche space by promoting dense, homogeneous vegetation. In contrast, grazing, except at very high intensity, maintains broad and spatially diverse microclimatic niches through heterogeneous vegetation structure, including bare soil patches and unconsumed vegetation. In terms of insect thermal tolerance, we expect little intraspecific but high interspecific variation in CTmax, and that community-level CTmax is higher in intensively managed grasslands that experience frequent and sudden temperature extremes, reflecting a thermal filter towards heat-tolerant species.
We combine synchronous UAV surveys with standardised insect suction sampling (biocoenometer) on three 1 m × 1 m subplots per plot across all 150 grassland Experimental Plots in all three Exploratory regions. A DJI Matrice 400 RTK drone equipped with a calibrated thermal infrared and RGB camera system, as well as stationary thermal cameras and temperature sensors, collect image data to map land surface temperatures at centimetre-scale resolution. Multi-height air temperature reference measurements taken simultaneously in the field are combined with UAV-derived surface temperatures and structural plant traits, including leaf area index, canopy height, and vegetation cover, in predictive models to estimate below-canopy air temperatures at the scale experienced by insects. Insect communities, focusing on Coleoptera, Heteroptera, and Orthoptera, are assessed and spatially linked to the thermal data of the same subplots. CTmax of selected common species is measured with a standardised ramping protocol.
Scientific assistants
