Habitat type shapes the restructuring of peatland dragonfly communities over two decades

Climate warming is restructuring insect communities, and its effects are uneven among species. Understanding which species gain, which decline and why requires long‐term data on community composition, interpreted through the traits of the species involved. Peatlands hold isolated populations of cold‐adapted odonates at the southern margin of their ranges, yet long‐term data on how their assemblages are changing remain scarce. Because peatland types differ in hydrology, degree of degradation and elevation, they also allow a test of whether habitat type shapes the direction and magnitude of community change. We compared historical and recent odonate assemblages across four peatland types in protected sites in Slovakia, accounting for differences in survey effort and seasonal timing between periods. Species richness did not decline in any biotope type and even increased in the two coldest ones, glacial lakes and open raised bogs. Assemblage composition nonetheless shifted between periods, and present‐day assemblages resembled one another more closely than historical ones did. Loss of conservation value, measured by the Dragonfly Biotic Index (a score combining species' rarity, threat status and sensitivity to disturbance), and a shift towards warm‐affinity species were confined to open raised bogs, the peatland type with the highest historical conservation value and the coldest assemblage. Five bog specialists of high conservation value declined in abundance by 54%–85%, and Aeshna subarctica fell from 8.3 to 2.0 individuals per visit at its only locality in the High Tatras. Across all peatland types, assemblages shifted towards more mobile species. These assemblages restructured over two decades without any loss of species richness, and the deterioration was greatest in the most strictly protected and least disturbed peatland type. More generally, insect communities can lose their most specialised and characteristic species while species counts stay stable or rise, so monitoring that relies on richness alone, even in protected areas, is likely to underestimate the effects of global change.