Monday, November 13, 2006

Nitrogen Reserves and Flows in an Inland Pacific Northwest Dry-Site Forest.

George Scherer, Jeff Hatten, and Darlene Zabowski. College of Forest Resources, Box 352100, Univ. of Washington, Seattle, WA 98195

Land managers in northwest inland areas are currently working to restore large forested areas to improve growth and sustainability. There are forest health issues related to nearly 100 years of fire exclusion, so we recently evaluated forest biomass and nitrogen pools and fluxes to improve our current understanding of inland forest nutrient cycles. Atmospheric deposition collection, stream flow measures, and resin core lysimetry was used to determine N fluxes. Biomass allometrics were used to calculate N pools from CHN analysis. For the one-year that we measured, we found N input of 2.5 kg ha yr and a stream loss of 1.1 kg ha yr. Litterfall contributed 11 kg N ha yr. Current above ground N pool was 545 kg ha and the soil-forest floor N pool was 6200 kg ha. This system appears to retain about 12 kg N ha yr suggesting a possible addition to reserves of 1100 kg N ha for the 100-year fire exclusion period. Biomass and N reserves for this site are within the range of variability found in the few studies from other inland forest settings. Additional work is needed on N-fixation processes in these forests. Knowledge from work will help land managers to minimize negative effects of restoration activities on dry inland forests and improve long term sustainability.

Handout (.ppt format, 5267.0 kb)