Observed vegetation changes in Danish dry heathlands since 2004

Danish heathland ecosystems have been monitored in the period from 2004 to 2021. The plant cover of all higher plants has been recorded using the pin-point method using a hierarchical sampling design with a total of 2515 plots within 102 dry heathlands, where 917 plots were revisited at least three times. The three most dominant species, heather, wavy hair-grass and black crowberry, all decreased in cover, although the decrease in heather cover was not significant in a two-tailed test. These decreasing trends in cover are worrying, since these three species are ecosystem engineers, and the structure and function of dry heathland ecosystems depend on these species being dominant. Conversely, the cover of purple moor-grass is increasing, and the increase of this tussock-forming grass may lead to significant ecosystem changes. Overall, the reported vegetation changes suggest a decreasing conservation status of Danish dry heathlands, and possible management actions to reverse this decreasing trend are discussed.