What are primary factors that control carbon storage, water and energy exchange in the North American boreal forest?
Boreal forest ecosystems store approximately one quarter of the total carbon found on land and are potentially important terrestrial sinks of “missing” or unaccounted for atmospheric carbon. Current global climate simulations predict high latitude areas will experience disproportionately higher temperature increases and an increase in fire frequency in the next few decades. One of the primary unanswered questions is how will carbon storage potential in these forests be altered by climate change? In addition, what impact will changes in carbon storage potential have for feedbacks on climate and the global carbon cycle?
Wildfires are the primary large-scale disturbance in these forests, with burn frequencies ranging from 50-200 year cycles. Our primary objective was to determine what factors control carbon balance in boreal forest stands as succession occurs following stand-replacing wildfires. We established a chronosequence of 6 boreal forest stands that range in time since a stand replacing wildfire occurred from 5- 150 years ago, all in the BOREAS Northern Study Area (NSA) outside Thompson , Manitoba . We directly measured carbon, water and energy fluxes in all 6 stands using tower-based micrometeorological technique called eddy covariance from 2002-2006. Eddy covariance provides an integrative measure of carbon fluxes into and out of the forest stands. These can be added up over the course of a day, month, season or year to determine if and when the forest is acting as a net carbon sink and successfully sequestering carbon from the atmosphere, or a net source of carbon to the atmosphere. We supplemented tower-based measurements with ground-based ecological measurements to determine specific contributions from vegetation and soil components in each stand.
In particular, we focused on the following questions: a) How large a carbon source are forests following burns? At what rate do forests lose CO 2 following burns? b) At what stage in recovery do forests switch from being carbon sources to carbon sink? c) For how long and at what rates do forests accumulate carbon? d) At what time, and for what reason do forests stop accumulating carbon?
Collaborators: Mike Goulden, Greg Winston, Andrew McMillan, Sue Trumbore Claudia Czimcik – UC-Irvine ; Jennifer Harden, Kristen Mainies, USGS- Menlo Park; Tom Gower, Brent Ewers, Ben Bond-Lamberty – Univeristy of Wisconsin-Madison; Hugo Veldhuis, Pascal Cyr, Environment Canada