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, rev eal both similarities and differences in response of contrasting Arctic eco systems to changes in temperature, light, and nutrient availability. Five d ifferent ecosystems were manipulated for 5-15 years by increasing air tempe rature with greenhouses, by decreasing light with shading, and by increasin g available N and P with fertilizers. The ecosystems at Abisko included eve rgreen-dominated heath and fellfield sites; at Toolik Lake they included we t sedge tundra, moist tussock tundra, and dry heath tundra. In all ecosyste ms, fertilizer treatment increased plant growth, production, and/ or biomas s. Plant responses to warming were smaller and occasionally nonsignificant. Responses to shading were generally nonsignificant after 3-6 years, althou gh after 9 years the tussock tundra showed significant decreases in biomass . In general, the ecosystems at Abisko were less responsive to nutrients an d more responsive to temperature than the ecosystems at Toolik Lake. Overal l, though, the sites were quite similar in their responses to the perturbat ions, increasing our confidence in predictions of response to climate chang e over large areas based on small-area studies.