Canada’s forests play an important role in the global carbon cycle. Forests exchange carbon dioxide with the atmosphere through the processes of photosynthesis, respiration, and decomposition. The boreal forest, which constitutes close to 80% of Canada’s forest area, is thought to be an important carbon sink for the atmosphere, as carbon is taken up by growing trees. Natural Resources Canada, Canadian Forest Service (NRCan, CFS) has tracked carbon stocks and fluxes in forest ecosystems since the 1980s and is obliged to report this information to the United Nations Framework Convention on Climate Change. Forest canopy carbon assimilation (photosynthesis) can be measured directly using portable infrared gas analyzers or quantified indirectly by measuring forest canopy water uptake (transpiration = water flux = sapflow). Plants combine carbon dioxide (CO2) from the atmosphere with water extracted from the soil to form sugars (plant food). Portable CO2 gas analyzers are used to measure foliage carbon dioxide uptake by various tree species; photosynthetic rates are calculated by using a real-time computer that considers numerous measured environmental and tree physiological variables in the calculations. These same analyzers, equipped with a soil chamber instead of a leaf chamber, can also measure carbon dioxide emissions (soil respiration) from the soil. Transpiration (water flux = sapflow) is measured by temperature-sensitive probes inserted into the sapwood of trees. The sapwood is the tree’s internal plumbing for transporting water taken from the soil by the roots. The water is then transported via the sapwood to the foliage where carbon assimilation (photosynthesis) occurs. The rate of sapflow is measured by electrically heating the water as it passes the first probe and then remeasuring the temperature as the water passes a second probe. The change in temperature of the water translates to a rate of water flow. If this rate of flow is known then a rate of canopy photosynthesis can be indirectly calculated without directly measuring CO2 uptake using a CO2 analyzer. All of these measurements require complex procedures, which are performed with the aid of specialized instruments. Carbon fixation is measured with a portable infrared gas analyzer, known as the LiCor 6400 Photosynthesis System (Image 1), which provides a measure of gas exchange at controlled temperature and light conditions. These data are combined with meteorological data and leaf area data to model annual carbon assimilation on a stand basis. Sapflow, or transpiration, is measured with Dynamax TDP 30 mm probes, (Image 2) which are inserted into the sapwood of the tree to measure the volume of water uptake on a daily basis.