Cattle grazing management decreases habitat quality for the bog fritillary butterfly Proclossiana eunomia in Prés de la Lienne nature reserve, Liege, Belgium
Published source details
Schtickzelle N., Turlure C. & Baguette M. (2007) Grazing management impacts on the viability of the threatened bog fritillary butterfly Proclossiana eunomia. Biological Conservation, 136, 651-660
Published source details Schtickzelle N., Turlure C. & Baguette M. (2007) Grazing management impacts on the viability of the threatened bog fritillary butterfly Proclossiana eunomia. Biological Conservation, 136, 651-660
In Europe, conservation of semi-natural habitats such as herb-rich ancient meadows and heathlands requires management such as livestock grazing to maintain habitat quality. In this study, a patchily spread population of the bog fritillary butterfly Proclossiana eunomia (a wet meadow specialist) in a nature reserve in southeast Belgium was monitored for 15 years (1992–2006), 11 before and four after the introduction of cattle grazing to some meadow patches. Assessments were made as to whether the grazing regime was appropriate in terms of affecting vegetation flinked to habitat quality for the butterfly, and the abundance and distribution of adult butterflies in response to vegetation characteristics.
Study site: The study was undertaken in Prés de la Lienne nature reserve, Liege province. The reserve comprises wet meadows where bistort Polygonum bistorta (the sole laval food plant in Belgium) grows. Two grazing areas were delimited (A and B) with seven discreet habitat patches (each 1.05-1.26 ha) surveyed.
Grazing: Galloway cattle were introduced in July 2002 and grazed selected areas year-round. Average grazing pressure (in Livestock Units/ha: 1 LU/ha = 1 cow) during the period July 2002–June 2004 (i.e. over two life cycles of P.eunomia) was 0.44 LU in area A and 0.24 LU in area B. Grazing intensity was higher over the summer months (0.56-0.75 LU/ha).
Data collection: Data were collected to assess grazing impact:
i) vegetation characteristics thought good indicators of habitat quality, i.e. % cover of P.bistorta and its main competitors (grasses and meadowsweet Filipendula ulmaria) and the numbers of grass tussocks (potential caterpillar basking sites ) and marsh thistle Cirsium palustre (nectar providers for adults);
ii) P.eunomia abundance and distribution among habitat patches each year, to calculate patch use, local recruitment and movement rates.
A total of 3,792 adult butterflies were marked over the 15 years. There was an average of 742 (re)captures of 253 marked adults per generation (15 generations). There was a clear negative impact of cattle grazing (even at the fairly low grazing intensities used) on abundance and recruitment: butterflies frequented ungrazed patches much more than grazed ones; fewer butterflies (around 74% less) emerged in grazed patches and emigration rate increased greatly.
Reasons for declines were primarily attributed to cattle decreasing bistort abundance (by about 25% cover; cover in ungrazed areas increased) and destroying grass tussocks used by caterpillars for basking. Despite the fairly low overall grazing intensity, grazing was intense in some patches where cattle congregated; vegetation was destroyed and soil exposed, inevitably destruction of butterfly eggs, caterpillars and pupae occurred.
The authors conclude that traditional mowing would probably be the best management option, however manual mowing is too expensive and mechanical mowing impractical due to the wet conditions. Grazing at this site thus seems the practical option; a lower grazing intensity (0.2 LU/ha) has been recommended in other studies, with grazing in autumn and winter but reduced or removed in spring and summer, i.e. a reversal of the regime used in this study. Retaining unmanaged patches (i.e. not managed on an annual basis) is recommended.
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