Impacts of fire and warming on ecosystem uptake in the boreal forest

Observations show that the amplitude of the annual atmospheric carbon dioxide cycle has increased. Lagged correlations between carbon dioxide, temperature, and vegetation suggest a modulation by ecosystem response, but the mechanisms remain unclear. Hypotheses include an early season uptake increase and/or winter respiration increase related to climate warming, and increased cycling in cooler conditions caused by disturbances such as fire. The first hypotheses suggest a positive feedback to regional warming, whereas the last suggests a negative Feedback. Here it is shown that fire, as it influences species composition, can serve to enhance the increase in early season uptake but that a crucial determinant for the sign of the feedback is the impact of climate change on soil moisture.