Combination of reclaimed and unreclaimed sites is the best practice for protection of aculeate Hymenoptera species on brown coal spoil heaps

The study focused on aculeate Hymenoptera recorded at 114 study plots on seven brown coal spoil heaps (reclaimed and under spontaneous succession) situated in the North Bohemian Brown Coal Basin, Czech Republic. In total, 2706 individuals of 212 species from 13 families were collected using Moericke traps. Of this number, 46 rare species (2 regionally extinct, 7 critically endangered, 14 endangered, and 23 vulnerable), 5 species protected by law, and 3 other rare species were recorded. Species typical of sand banks and open landscape were most numerous. The communities were dominated by Lasioglossum species, Diodontus minutus and Bembecinus tridens on unreclaimed sites, and Apis mellifera, Lasioglossum pauxillum, and Osmia rufohirta on reclaimed sites. Unreclaimed sites hosted twice as many rare species at four times greater abundances. Rare species occurred there more frequently than at reclaimed sites. Species known as regionally extinct, Evagetes littoralis and Nomada minuscula, were found only on unreclaimed sites. Redundancy analysis showed that especially threatened species are connected with sandy sites small in area and with sparse vegetation cover. The number of rare species slowly increased with age, but young sites, too, could be very rich. It is recommended to combine succession and reclamation approaches to create suitable nesting habitats, refuges, and food resources. It is essential to maintain a fine mosaic of habitats in various (above all young) successional stages.