Habitat characteristics,stage structure and reproduction of colline and montane populations of the threatened species <Emphasis Type="Italic">Arnica montana</Emphasis>

Arnica montana, a characteristic plant of nutrient-poor grasslands, has strongly declined during the last decades, particularly at lower altitudes. To gain insights into the underlying reasons for this decline, we recorded differences in size, stage structure and reproductive traits between 21 colline populations of A. montana in the Ardennes-Eifel region (280–600 m a.s.l.) and 10 montane populations in the Vosges Mountains (1,200 m a.s.l.). Community composition of the Violion caninae vegetation at colline sites and Nardion strictae vegetation at montane sites indicated that temperature and moisture were the main abiotic factors differentiating between low and high altitudinal relevées. The proportion of flowering rosettes decreased with altitude, indicating a shift from sexual reproduction to clonal growth. In contrast to expectation, Ellenberg values for nutrient availability as well as the proportion of young rosettes and population size did not differ between colline and montane populations. However, population size decreased with nutrient availability, indicating eutrophication as the reason for population decline. In small populations, plant density, the proportion of flowering rosettes, the number of flowerheads per rosette and the number of seeds per flowerhead were lower, indicating less suitable conditions. Thus, preventing further eutrophication in both colline and montane populations will be crucial for the conservation of the species. Reduced reproduction may not be important for the population dynamics of this clonal plant in the short term, but could affect genetic diversity and survival in the long term.