Primary Production in Arctic Ecosystems: Interacting Mechanisms of Response to Climate Change

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In Alaskan tundra ecosystems, shrubs and mosses play key roles in regulating surface energy balance in both winter and summer, and are key determinants of the uptake and turnover of limiting elements in the vegetation. Shrub and moss abundance is also expected to change dramatically with climate warming, but it is still unclear and controversial whether the warming of the last few decades has actually caused any changes thus far. This research will use long-term experimental manipulations of the tundra environment at Toolik Lake, Alaska, where shrub and moss abundance have changed dramatically, to improve our understanding of controls on the rate of change in shrub and moss abundance, and on the timing of the sequence of changes in climate, shrub and moss abundance, canopy architecture, and surface microclimate. One product will be demographically-based models of shrub and moss growth and canopy architecture in relation to climate. A second objective is to document annual variation in production, biomass, and species composition at several tundra sites in northern Alaska, so as to quantify the normal "background" annual variation in these characteristics. By doing the work at sites where similar measurements were made during the 1960s and 1970s, it will be possible to determine whether the changes over 3 or 4 decades exceed the annual variation or whether annual variation exceeds any long-term trends. A third objective is to continue a series of ongoing synthesis activities aimed at improving understanding of climate change effects at the level of the entire Arctic as well as globally.