GRAHAM HART Abstract The Pyreneen distribution of Lycaena helle was studied in 1995 and 1996 by reviewing the literature and extensive field studies, which found many new sites. There is one single centre of population in the Pyreneen Mountains, which covers an area of about 500km2. The whole of this distribution area could be one very large metapopulation (at least in 1996) which due to habitat change is in danger of serious fragmentation, isolation and loss of colonies. The technique used for measuring habitat suitability and population density was the study of oviposition sites and egg numbers using line transects and recording quadrats. The ideal oviposition situation is of a mid range moisture content, vegetation of a heterogeneous height, a Boorman disc height of 10 to 20cm (though a much wider range is used) and â€˜apparentâ€™ leaves of the larval food plant. The eggs are always laid in a warm microclimate situation usually in hollows in the vegetation. The presence of tufts or tussocks of grass with lots of dead leaves around the tussock, or dead leaves of Juncus and Carex was very important. In 2012 a new study was undertaken using the same methods at the two main study sites of 1996. The declines were of 90% and 98%. Just 5km away there are other sites that do not seem to have declined, so these and other sites with no apparent decline were also studied using the same technique. Even here where the populations seemed healthy the egg numbers were at best only one third of the best transect recorded in 1996, this suggests either that 1996 was an exceptional year or that all the populations are in fact declining. The changes in the habitat from 1996 to 2012 were recorded. The effects of grazing and abandonment are discussed, at one of the two main sites overgrazing is strongly implicated in the population decline (90% reduction). At the other site abandonment and ecological succession are implicated (98% reduction). It is suggested that at least with Molinea caerulea tussock dominated sites rotational management using grazing or cutting and removal of large tussocks to take the habitat back to an earlier successional state may be a good management strategy. We have to accept that we cannot have all the habitat suitable all the time. We need also to differentiate the type of grazing required, high level and all summer for restoration of severely degraded habitat and light and precisely timed, for maintenance of a colony. The use of grazing exclosures in heavily grazed areas may also offer an important way of increasing available habitat and providing stepping stone habitats linking different areas for the maintenance of a metapopulation structure. A habitat improvement and restoration project was started in the autumn on 2012 at the two main study sites of 1996 and at several other nearby sites. Discussions are also in progress to extend management work to other important areas and with farmers and landowners to have more sympathetic management on the landscape scale to reduce or hopefully stop the fragmentation of the metapopulation(s).This project will be ongoing, we aim to repeat the egg transects for the next five years to measure the success of the management.
Published on Oct 16, 2013