Question 1. How does climate variability affect the openness and connectivity of arctic ecosystems?

Our research on how climate variability affects the openness and connectivity of arctic ecosystems focuses on vegetation and biogeochemical cycles in moist acidic tundra along a nutrient gradient, in warming plots, and in nearby Alder stands.

Arctic terrestrial ecosystems are typically relatively closed, both biogeochemically and in community structure for vascular plants. Fertilization experiments demonstrate co-limitation by N and P, and the removal of nutrient limitation typically results in a shift in plant functional types towards woody deciduous shrubs with variable effects on tundra biogeochemistry. What we do not yet understand is how climate variability will affect nutrient inputs and turnover rates, and thus ecosystem openness and connectivity. Similarly, we do not know how climate variability will affect community openness or its functional consequences. In three new activities we will use models, observations, and experiments to answer the following questions:

How does variable nutrient availability affect biogeochemical connectivity?

To what degree can N fixation compensate for variation in N inputs?

How does climate variability affect plant community composition and in turn ecosystem function?

Fireweed (Chamerion angustifolium) has appeared in our high N plots in both tussock (left) and dry heath (right) tundra.  This species is more commonly seen in disturbed areas in boreal forests or along roads but has never been found in our experimental plots.  The occurrence of fireweed is confined to only the high fertilizer plots.