Effects of experimental warming on arctic willows (Salix spp.): A comparison of responses from the Canadian High Arctic, Alaskan Arctic, and Swedish Subarctic

Three species of dwarf, prostrate willow (Salix arctica, S. rotundifolia and S. herbacea) were subjected to experimental summer warming in high arctic Canada, arctic Alaska, and subarctic Sweden, respectively, as part of the International Tundra Experiment. Phenological and growth responses of these species were compared for the second season of the experiment. Stigmas became receptive and pollen dispersal occurred significantly earlier for S. rotundifolia and S. herbacea in the ITEX open-top chambers, but not for S. arctica. Warming had no effect on the timing of seed dispersal, leaf yellowing, or leaf senescence. The length and dry weight of the largest leaves were greater for warmed plants, and was significant for S. rotundifolia. The number of catkins/plot did not differ among species or treatments, but the fruit:newer ratio was reduced in the experimental plots.