Habitats of pre-hibernating gregarious larvae of the endangered Marsh Fritillary butterfly (Euphydryas aurinia) were studied in field in Western Bohemia, Czech Republic. The species inhabits moist seminatural meadows managed by light grazing and haymaking; the only local host plant is Succisa pratensis. The redundancy analyses of the vegetation composition (around 166 nest-bearing and 381 unoccupied host plants) showed that nest presence was positively associated with short cushion-forming grasses (esp. Nardus stricta). It was negatively associated with competitively superior tall grasses (e.g., Deschampsia caespitosa) and tall herbs. Comparison of Ellenberg's indicator values of vegetation in occupied vs. unoccupied plots revealed that the nests were more often found in drier, nitrogen-poorer and more acidic conditions than unoccupied plants. Multiple regressions of nest presence against architecture of the host plants (170 occupied, 1280 unoccupied) revealed that the nests were associated with densely clumped host plants, low to medium height of sward and mechanical disturbance. The patterns agree with our knowledge of the biology of the larvae: short sward (related to low nitrogen, humidity, and low pH) facilitates larval basking; high host density reduces the likelihood of starvation. Sod disturbance facilitates host plant germination. The conditions favourable for the nests were also favourable for the host plant, but the plants grew in broader range of conditions than that occupied by the nests. The abandoning of a site results into a situation when the conditions first become intolerable for the butterfly, and ultimately for the plant. Since grazing and mowing have a different impact on vegetation composition and architecture, we propose that the studied populations have persisted in a semi-dynamic state in the two modes of management. Conservation management should mimic the dynamics of traditional land use on the smaller scales of extant colonies.
A syntaxonomical revision of meadows of the Molinion caeruleae Koch 1926 alliance in the Czech Republic is presented. Of ten associations reported previously for the Czech Republic only two were distinguished using the Cocktail method – Molinietum caeruleae Koch 1926 and Junco effusi-Molinietum caeruleae Tüxen 1954. The former occurs on more base-rich soils, while the latter is found in more acidic habitats and characterized by the occurrence of species of Nardus grasslands. Results of this classification were compared with classifications of Molinion meadows for other countries of Central Europe. Main environmental gradients responsible for variation in species composition of Czech Molinion meadows were revealed by detrended correspondence analysis. For interpretation of these gradients correlations with Ellenberg indicator values and altitude were used. The main gradient positively correlates with soil base status, continentality, temperature and nutrients, and negatively with altitude.