Range shifts and global warming: ecological responses of Empetrum nigrum L. to experimental warming at its northern (high Arctic) and southern (Atlantic) geographical range margin

摘要

Global change is expected to lead to range shifts of plant species. The ecological mechanismsunderpinning these shifts are currently not well understood. Here, we compared ecological responses possibly underlying southern range contraction and northern range expansion ofEmpetrum nigrum, a key species in northern heathlands, which may be related to globalchange. We hypothesized a negative response to warming in the ‘south’ (i.e. the Netherlands)and a positive response at the northern range margin (the tundra on Svalbard). Open topchambers (OTCs) were used to simulate global warming. In the ‘south’, OTC warming causedenhanced shoot growth and growth rate, biomass increment, advanced phenology, larger andheavier berries of Empetrum, while its growing season was extended by 75 days. Under OTCwarming co-occurring Calluna vulgaris also showed an increased growing season length (by98 days) as well as increased shoot growth rate and biomass growth, plant cover and height.Still, we found no evidence for increased competitiveness relative to Empetrum. In the ‘north’,Empetrum responded with increased shoot and biomass growth, enhanced berry developmentand ripening to warming. These responses exceeded those of co-occurring Cassiope tetragonawith the exception of its biomass response. The direct and indirect ecological responses founddo not readily explain the observed northward retreat of Empetrum at the southern rangemargin. The direct ecological responses found at its northern range margin are, on the otherhand, in line with the increased occurrences of this species on Svalbard.