Annual estimates of net ecosystem exchange (NEE) of carbon dioxide (CO2) for the BOREAS forested tower sites remains 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 forests 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 forests in the world. We will compare three approaches for estimating NEE: (1) the difference between net primary production (NPP) and heterotrophic respiration (RH) portion 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 measurements. 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.

Publications
Gower, S.T., O. Krankina, R.J. Olson, M. Apps, S. Linder, and C. Wang. 2000. Net primary production and carbon allocation patterns of boreal forest ecosystems. Ecological Applications (In Press).

Kucharik, C.J., J.A. Foley, C. Delire, V.A. Fisher, M.T. Coe, J.D. Lenters, C. Young-Molling, J. M. Norman, N. Ramankutty, S.T. Gower. 1999. The IBIS-2 Dynamic biosphere model: model formulation and evaluation. Global Biogeochemical Cycles 14:795-825.

Stith T. Gower, Amanda Hunter, John Campbell, Jason Vogel, Hugo Veldhuis, Jennifer Harden, Sue Trumbore, John M. Norman, Chris J. Kucharik.. 2000. Nutrient dynamics of the southern and northern BOREAS boreal forests. Ecoscience (in press)