Specialist butterflies are becoming increasingly rare in Britain as the semi-natural habitats which they depend upon become fragmented or disappear. As butterflies are warmth-loving species the greatest species diversity tends to be found in the south of Britain, but it is in southern England where the pressure for land is greatest. However, some of Britain’s rare butterfly species are surviving in the cooler north where semi-natural habitats tend to be more abundant, and where suitable micro-climate characteristics can be found.
One such species is the chequered skipper (Carterocephalus palaemon Pallas) which is now confined to an area of the Great Glen in Lochaber where the northern climate is moderated by the large water bodies of Loch Linnhe, Loch Lochy, Loch Arkaig and Loch Eil. This butterfly feeds on purple moor-grass in flushed locations sheltered by woodland.
This area is also rich in other butterfly species including the pearl-bordered fritillary (Boloria euphrosyne L.), another UKBAP priority species. This species feeds on violets that grows within sparse bracken stands in sheltered locations, it is found more widely in Britain then the chequered skipper.
Loch Arkaig butterfly reserve
In recognition of the richness of the area, Forestry Commission Scotland (FCS), in partnership with Butterfly Conservation are managing a large site on the shores of Loch Arkaig as a butterfly reserve. The site consists of an area of open ground with scattered woodland, and two blocks of mature Sitka spruce (Picea sitchensis (Bong.) Carr.) dominated conifer plantation.
At this site, the majority of the butterflies are to be found in the open areas, especially among the scattered woodland where there is more shelter. In the past, sheep and deer have grazed the area, but the grazing regime has been changed to summer grazing by cattle only. The aim is to improve the vegetation structure for pearl-bordered fritillary larvae, increase the nectar sources and stimulate tree regeneration on the more exposed parts of the site. Provision of such precise conditions requires careful management and the effect of the management prescription designed to deliver these needs to be monitored.
Forest Research have designed and are implementing the monitoring at the butterfly reserve. Using permanently marked quadrats, vegetation composition is being assessed annually in early summer, with the aim of detecting significant changes in butterfly food-plant availability. On a broader scale, the occurrence of nectar sources and tree seedlings are also being assessed across the site through a series of permanently marked transects.
In the conifer plantation, the FCS have embarked upon a process of restructuring, with sequential areas being felled and replanted over the next 30 years. As the woodland is restructured, open areas will be created, if only temporarily. For a time, these might support the food plants and nectar sources for the target butterflies. Harvested coupes are being monitored from shortly after felling until the replacement crop closes canopy, to chart the development and decline of ground vegetation. This should identify whether suitable ground cover can develop, at what time this is likely to happen, and for how long it will persist. Such information will allow timing of felling to be scheduled so as to provide a continuity of butterfly habitat throughout the forested area.
Work is funded by Forestry Commission and Butterfly Conservation (BC). Reserve management is carried out by Forestry Commission Scotland (FCS) with guidance from Butterfly Conservation. Forest Research leads the research and is assisted by BC and FCS.
