Effects of Organic Matter Removal and Competing Vegetation Control On Soil Carbon and Nitrogen Pools in a Pacific Northwest Douglas-Fir Plantation.

Current interest in the use of woody biomass for energy production may lead to higher volumes of organic matter removal during timber harvest with the additional removal of branches and foliage, thus resulting in higher carbon and nutrient removal than occurs in traditional, bole only harvest. The potential for such higher harvest intensity necessitates a careful evaluation of the influence of forest management practices on long-term forest productivity. In this study, soil carbon and nitrogen were measured to a depth of one meter at the Fall River long-term soil productivity site for bole only harvest with and without competing vegetation control (B0+VC, BO-VC) and for total tree plus harvest with vegetation control (TTP+VC). Four plots per treatment were each sampled in six random subplot locations. Mineral soil sampling was done in five depth increments: 0-15 cm, 15-30 cm, 30-45 cm, 45-60 cm, and 60-100 cm. Forest floor samples were also collected. Samples were dried at 60°C and mineral soils separated into >4.75 mm and <4.75 mm fractions. Material <4.75 mm was ground and processed in a CHN analyzer.