Narrow climate and habitat envelope affect the survival of relict populations of a northern Arnica angustifolia

Abstract

Many species require certain habitat and climate features, especially at range limits. Because of climate warming, isolated relict southern populations of arctic-alpine species could lose their viability. Arnica angustifolia is a rare, clonal northern plant which has distinct populations far away from its central distribution area. I explored its population viability in relation to habitat properties and local temperature regimes using demographic and temperature data collected during 1996–2009 from six southern populations. The data were analyzed with matrix population modeling. Both projected and stochastic population growth rates showed spatiotemporal variation, and indicated decreasing population trends. The population growth rate was most sensitive to the survival of small sized vegetative rosettes, emphasizing the importance of rosette size for fitness. High temperatures and habitat closure were the main threats to viability of Arnica. First, high temperatures during the previous and current growing seasons had a negative impact on rosette size and survival of ramets. Second, high coverage of deciduous shrubs and tall mosses decreased the survival and size of rosettes. Obviously, the viability of populations can be enhanced by habitat amelioration. Population isolation and restricted recruitment and habitat specificity decrease the possibilities for environmental tracking. Further, overgrowth will decrease the availability of growing space inside the populations. Consequently, the long term survival of southern populations in Arnica largely depends on both the ability of species to adapt consequences of changing temperature regimes and the speed of habitat deterioration.