In the past 100 years dragonflies declined and recovered by habitat restoration and climate change

Abstract

The availability of opportunistic dragonfly data in the Netherlands spanning >100 years gave us the opportunity to quantitatively assess long term changes in range size. We estimated changes in the number of occupied 5 km × 5 km sites by applying a modified List Length method, which takes into account changes in observation effort. Trends were assessed for nearly all Dutch dragonfly species and the trends were then summarised in Multi-Species Indicators by taking the geometric mean of the species indices. Overall, dragonflies severely declined in range size between the periods 1850–1950 and 1975–1990. In the period thereafter, strong increases happened, during which many species compensated their earlier losses. The factors driving the changes in dragonflies shifted over time. Until 1975 dragonfly species declined due to deterioration of water systems. After 1975 both climate change and habitat restoration contributed to the recovery of many species. Restoration of dragonfly communities was most successful in running water and least effective in moorland pools.