S.T. Gower (P.I.), J.M. Norman, C.J. Kucharik. University of Wisconsin - Madison
Annual estimates of net ecosystem exchange (NEE) of carbon dioxide (CO2) for the BOREAS forested tower sites remain uncertain. The uncertainties are the result of: (i) logistical difficulties of compiling numerous data sources from PI's, (ii) the lack of standardized climate data needed to run process models to interpolate between measurement periods, (iii) an incomplete understanding of the influence of carbon allocation on soil carbon dynamics and (iv) correctly modeling canopy photosynthesis for boreal forest canopies with non random distribution of foliage. We, in close collaboration with a small working group, propose to address these issues and develop complete annual carbon budgets for the BOREAS eddy flux tower sites in forests and other boreal forest in the world. We will compare three approaches for estimating NEE: 91) the difference between net primary production (NPP) and heterotrophic respiration (RH) potion of the soil surface CO2 flux, (2) process model simulations and (3) eddy flux measurements. The three approaches will allow us to determine the contribution of each ecosystem component to NEE in contrasting climates and ecosystems and place constraints on NEE obtained from eddy covariance flux measurement. A second objective is to compile data from BOREAS and other boreal forests of the world to develop carbon allocation and light use efficiency (LUE) coefficients and use regression analysis and ecosystem process models to determine the influence of environmental and ecological (i.e. functional plant groups, evergreen vs. deciduous) factors on allocation and LUE coefficients. Improved values of LUE for each vegetation component and greater understanding of carbon allocation dynamics will greatly improve global process models, and when combined with remote sensing imagery, provide improved annual estimates of NEE for the boreal forest.
Objectives
Calculate annual carbon budgets, using instantaneous chamber-based flux measurement of respiration and stand0-level measurements of net primary production, for the six BOREAS mature forests (aspen, jack pine and black spruce at the southern study area (SSA) and northern study area (NSA) and for other "data rich" boreal forests of the world.
Compare annual estimates of net ecosystem exchange (NEE) of CO2 obtained from eddy flux towers and the combination of chamber-based flux measurements of respiration and stand-level measurements of net primary production. The analysis will include a critical assessment of the accuracy and sources of error of both approaches.
Use process-based ecosystem models to examine the influence of (i) carbon allocation on net primary production and net ecosystem exchange of CO2 and (ii) canopy architecture (i.e. non-random distribution of foliage).
Compile carbon budgets for boreal forests and peatlands and calculate carbon allocation coefficients and light use efficiency coefficients for the major forest functional groups (broad-leafed deciduous, needle-leaved evergreen, and needle-leaved deciduous).
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