Measuring Forest Floor, Mineral Soil, and Root Carbon Stocks

Abstract

In forest and wildland ecosystems, forest floor and soil carbon (C) comprise a large C pool that is often of similar magnitude to or greater than aboveground C storage. These C pools often change slowly over time, but they are susceptible to rapid release to the atmosphere following natural or human-caused disturbances. Accurate estimates of these pools are needed both to quantify current ecosystem C storage and to understand the potential for future soil C sequestration or release due to disturbance, reforestation, or global change factors. This chapter describes a field sampling approach for quantifying C stocks in forest floor and mineral soil horizons and in live and dead coarse root biomass. The volumetric pit method described for soil horizons is time consuming and labor intensive, but is known to produce the least bias, especially for soils with high stone and rock content. The method described is designed for upland soils, but alternatives that can be used in wetland soils are listed. Key considerations for any sampling of soil C stocks are obtaining accurate volumes and densities for soil materials sampled and sampling to sufficient depth to obtain the vast majority of organic soil C. Careful sampling of soil C stocks at periodic intervals will provide information that helps us model changes in soil C due to management, disturbance and global change and helps validate rates of net ecosystem C exchange measured by flux towers and other techniques.