Butterflies: heathland and raised bog are losing their open character
Water draw-down and the encroachment of grass and trees are causing the butterflies of dry and wet heath habitats to decline.
Trends
The numbers of grayling, silver-studded blue and cranberry fritillary are lower than in 1950. Since 1992 the silver-studded blue has continued to decline but the other two species have not. The grayling occurs in dry heath, the silver-studded blue requires a mosaic of dry and damp heath, and the cranberry fritillary occurs in wet heath, near fens and in raised bogs. Thus the decline in butterflies is apparent in all components of heathland.
Causes
The decline since 1950 is attributable to water draw-down and the encroachment of grasses and trees. The host plants of these butterfly species have vanished and the vegetation structure has become less suitable for them. Some species, among them the silver-studded blue, require open patches in the vegetation, where they can sun themselves. These patches disappear when grasses encroach and when there are too many old heather plants. Good management can improve the situation, however.
The plan to protect butterflies of peat habitats includes various measures intended to protect the cranberry fritillary and other species of raised bogs.
All three butterfly species are on the Red List of butterflies.
Technical note
The indices for the three species are from the Ecological Monitoring Network's national network for monitoring butterflies. The benchmark year is 1950 (=100). The changes since 1992 have been statistically tested.
References
- LNV (1990). Beschermingsplan dagvlinders. Ministerie van Landbouw, Natuurbeheer en Visserij. Directie Natuurbeheer. Den Haag.
- LNV (2001). Beschermingsplan veenvlinders 2001-2005. Directie Natuurbeheer. Ministerie van Landbouw, Natuurbeheer en Visserij. Directie Natuurbeheer. Wageningen.
- Swaay, C. van, R. Ketelaar en D. Groenendijk (2002). Dagvlinders en libellen onder de meetlat: jaarverslag 2001. Rapport VS2002.010. De Vlinderstichting. Wageningen.
