Biodiversity at Linnaeus' birthplace in the parish of Stenbrohult, southern Sweden. 5. Butterflies and burnet moths.

Författare

Sven Nilsson
Markus Franzén

Summary, in English

We counted butterflies in almost all open grasslands in an area of 8000 hectare over five years (2001-2005) in the central part of the parish of Stenbrohult, southern Sweden (Fig. 1; 56 degrees 37' N, 14 degrees 11' O). This area is currently dominated by forests. Grasslands, mainly grazed by cattle and horses, only cover about 6 % of the area. The study area consisted of 18 farms, most ot them are surrounded by coniferous forests and some bordering lakes. Three farms are protected as nature reserves and more reserves are planned for at least four more farms. Habitat types were mapped on each farm (Table 1). Standardized transects counts, with 6 - 8 annual visits evenly spread over the period from the middle of May to the middle of August, were performed in all 18 farms. The annual maximal counts of butterflies and burnet moths at one occasion in each subarea and year are presented (Appendix). The sum of these were 56 682 individuals of 46 species of butterflies and 2 791 individuals of 4 species of burnet moths. One individual each of two additional species, Limenitis populi in 2000 and Issoria lathonia in 2003, was found outside the standardized counts. Many species were recorded in low numbers in 2001 and high in 2003, some increasing by an order of magnitude. There were also a very high variation of species richness and numbers of individual species between the different farms. The highest number of species were found on farms in the central part of the study-area and on farms with traditionally managed and unfertilized hay-meadows. We discuss the possible causes of these variations. Our results show that monitoring schemes must include many plots and years to reveal population trends due to land management changes. Many species occurred in low numbers and since suitable habitats have decreased they may constitute an extinction debt, e.g. Pyrgus malvae, Leptidea sinapis, Aporia crataegi, Coenonympha pamphilus, Lasiommata maera, Polyommatus semiargus and Zygeana.filipendulae. We propose measures to prevent this debt to be realised.

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