HOW DO WE STUDY CARBON SEQUESTRATION

Carbon based biomass accumulates above and below ground in forests of the northwestern U.S.  Mathematical formulae are used to estimate above ground bomass.  The Goltz equations have been used in the past to estimate standing biomass of northwest conifers, but at our research in Fall River, we found it more appropriate to generate our own mathematicial relationships for the estimation of forest biomass above ground.  

An important question in current forest management practices is whether or not fertilization can increase carbon sequestration.  The basic question is whether or not an increase in limiting nutrients will increase forest productivity and soil carbon sequestration.  In our studies we apply urea fertilizer (Figure 1) to the forest.  Urea may be applied manually (Figure 2) or by air.  As Figure 1 shows, urea contains nitrogen, but only half as many parts of carbon.  Carbon is present in much larger quantities than nitrogen with C/N ratios of plant tissue and soils commonly ranging from 10 to 40.  The major carbon source, of course, is fixation of carbon dioxide from the atmosphere via the process of photosynthesis.  







 











 




The stem cross section below shows the effect of urea on tree growth.  Immediatly after the application of 200 pounds per acre of urea fertilizer, tree growth increased.  The result of this is an obvious increase in above ground carbon sequestration.  Sequestration in the soil is not as easy to measure and the mechanisms of carbon sequestration in the soil are not straight forward.  For instance, increased growth below ground could be manifested as root diameter increases or an increase in root exudates associated with the rhizosphere.  In either case, microbial consumption and solubility and adsorption properties of the soil will influence the longeivity of this carbon in the soil.  Some carbon may flush rapidly through the soil, whereas other carbon may be processed and made more recalcitrant.  More stable and insoluble forms of carbon have a much longer residency time in the soil.