Accounting for variation in root wood density and percent carbon in belowground carbon estimates
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Little is known about belowground biomass and carbon in tanoak. Although tanoaks rarely provide merchantable wood, an assessment of belowground carbon loss due to tanoak removal and Sudden Oak Death will inform conservation and management decisions in redwood-tanoak ecosystems.
The carbon content of woody biomass is a function of density and the proportion of carbon in dry biomass. Whole-tree basic wood density or specific gravity estimates are often available to facilitate calculation of forest biomass, and contemporary carbon analyses generally assume that carbon comprises 50 percent of the dry biomass for the whole tree. Less is known about root wood density and carbon, or variations within root systems. Quantifying root wood density and carbon content changes along the length of a root will enable more accurate estimation of belowground carbon, and support development of equations predicting carbon from easily measurable aboveground variables, such as dbh.
To analyze root density and carbon content at different locations within root systems, tanoak trees were first removed using an excavator. Root wood samples were taken from four locations within the root system: within the stump (aboveground), within the lignotuber, at the start of the root (adjacent to the lignotuber) and at the end of the root (near tip). We did not detect significant differences in root wood density between samples collected at different distances from the stem or between different sizes of roots. Percent carbon was highest at the sample farthest from the lignotuber, while samples from the other locations were not statistically different. Root carbon also varied among root systems sampled.