Data from: Importance of grassy and forest non-crop habitat islands for overwintering of ground-dwelling arthropods in agricultural landscapes: a multi-taxa approach

The study was carried out during February and March 2019 in two intensive agricultural regions situated in the Czech Republic, Central Europe (Neratovicko and Sedlčansko). Within each study area, we selected eight NCHI, i.e., small- to medium-sized (0.18–1.74 ha) non-crop habitat fragments that were fully surrounded by arable land. For each NCHI we sampled arthropod assemblages at three locations: 20 m inside the arable land (henceforth ‘arable’), on the edge of NCHI (henceforth ‘boundary’) and 10 m inside the NCHI (henceforth ‘non-crop’). Based on our previous experience from the same study system, we assume that sampling position 20 m into arable land from the edge resemble arthropod assemblages inhabiting arable field interiors. The distance within NCHI was limited to 10 m as the smallest NCHI in our study were just slightly over 20 m wide.Arthropod sampling The distribution of ground-dwelling arthropods, specifically, carabid beetles (Carabidae), rove beetles (Staphylinidae), spiders (Aranea) and myriapods (Diplopoda and Chilopoda), was investigated during late winter using two different sampling methods. To investigate the spatial distribution of arthropods overwintering in the upper soil layer, we performed individual searches within the soil (quadrat sampling). Quadrat sampling was performed between 26th February and 1st March 2019 using eight sampling squares per location (384 squares in total) placed along a 20 m transect placed in parallel to the NCHI boundary. Squares covering 0.25 m2 (0.5 × 0.5 m) were delimited from the surroundings using a metallic frame, the soil inside the square was disturbed to the depth of 10 cm using a small hand hoe, and all visible arthropods were actively searched by one observer and collected using aspirators during seven minutes. All sites were sampled by the same group of four observers (two squares per location per observer) to minimize potential observer biases. To investigate the distribution of arthropods active on soil surface we used pitfall traps. Traps were made of transparent plastic cups (9.4 cm in diameter, 14.4 cm depth) covered with an aluminium roof and filled with propylene glycol diluted with water (1:2 ratio) as preservation fluid. The traps were exposed from 26th February to 22nd March 2019, before most arthropods begin to disperse from their overwintering sites. A set of three pitfall traps distant 10 m from each other were installed at each location (a total of 144 pitfall traps, three were lost during the exposure period; Fig. 1b).Samples collected with both sampling methods were frozen at −22 °C, subsequently sorted to higher taxa, and all adults from the selected taxa and also juvenile myriapods were identified to the species level by specialists. In addition, juvenile spiders collected by quadrat sampling were also identified to the species or genus level