Response of Arctic ecosystems to climate change: results of long-term field experiments in Sweden and Alaska

Long-term field experiments at Abisko, Sweden, and Toolik Lake, Alaska, reveal both similarities and differences in response of contrasting Arctic ecosystems to changes in temperature, light, and nutrient availability. Five different ecosystems were manipulated for 5-15 years by increasing air temperature with greenhouses, by decreasing light with shading, and by increasing available N and P with fertilizers. The ecosystems at Abisko included evergreen-dominated heath and fellfield sites; at Toolik Lake they included wet sedge tundra, moist tussock tundra, and dry heath tundra. In all ecosystems, fertilizer treatment increased plant growth, production, and/ or biomass. Plant responses to warming were smaller and occasionally nonsignificant. Responses to shading were generally nonsignificant after 3-6 years, although after 9 years the tussock tundra showed significant decreases in biomass. In general, the ecosystems at Abisko were less responsive to nutrients and more responsive to temperature than the ecosystems at Toolik Lake. Overall, though, the sites were quite similar in their responses to the perturbations, increasing our confidence in predictions of response to climate change over large areas based on small-area studies.