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Fall River Long-term Productivity Study : Predictions of Pre-harvest Biomass and Nutrient Pools K. Petersen, B. Strahm, C. Licata, B. Flaming, E. Sucre, J. Forcier, Rob Harrison, College of Forest resources, University of Washington; Thomas A. Terry, Weyerhaeuser Company; Constance A. Harrington, U.S.D.A. Forest Service, PNWRS Biomass and Nutrient Content Sampling Methodology A comparison of site-specific allometric equations for estimating pre-harvest above-ground biomass with the Gholz equations (Gholz et al. 1979) for estimating biomass showed an ~14% difference between the estimates. This emphasizes the importance of developing models on a site by site basis. Site Features Soil Series: Boistfort (volcanic parent material) 50 yr. site index: 130 ft. (40 m) Slope: 10% Aspect: West Site area: 12.24 ha Map Source: http://wwwflag.wr.usgs.gov/USGSFlag/Data/maps/Washington.gifhttp://wwwflag.wr.usgs.gov/USGSFlag/Data/maps/Washington.gif McDonald Tree Farm owned by Weyerhaeuser Company Location: Section 2/11,T14N, R6W Pacific County, Washington Site History Western Hemlock was the dominant species at harvest in 1952 and 1953. The unit was replanted in 1953 and 1954 with Douglas-fir seedlings at 886 tpa. Naturally regenerating hemlock increased tpa to 905. The stand was precommercially thinned to a tpa of 494 in 1971. Approximately 1800 kg N/ha was applied as urea fertilizer over the course of the 1953-1999 rotation. The stand was harvested in 1999 according to a plan to study the effects of various management treatments on soil processes, nutrient cycling, and Douglas-fir productivity over a 40 year stand rotation. Works Cited: Gholz, HL,Grier CC, Campbell AG, and Brown AT. 1979. Research Paper 41, Forest Research Lab, School of Forestry, Oregon State University, Corvallis, OR Estimated preharvest distribution of biomass and pools of C and N in the above-ground portion of the forest system for each tree species Conclusions Establishment of accurate estimates for preharvest biomass and elemental pools allows for comparisons of biomass, C, and N pools in a spatial and temporal context. It is critical to develop site-specific allometric equations for estimating biomass. Future work will include estimating the biomass and nutrient content of 5 th year trees to determine the effects of competing vegetation control. Photo above depicts1999 Preharvest stand conditions Acknowledgements Funding for the Fall River Long-term Productivity Study was made possible through grants from the National Council for Air and Stream Improvement (NCASI) and the Olympic Natural Resource Council. Collaboration with the USDA Forest Service PNW Research Station Olympia Lab and the Stand Management Cooperative has been invaluable to this research. Also, wed like to thank Dongsen Xue of UW Analytical Laboratory Services for his assistance. Finally, we express thanks to Weyerhaeuser Company for continued support of this project. For additional information on details of the Fall River Long-term Productivity Study please visit the following web address: http://soilslab.cfr.washington.edu/LTSP_FallRiver/ 30 Douglas-fir (15-80.1 cm dbh) and 11 Western hemlock (20-61.7cm dbh) were selected for predicting the biomass of the 12.24 ha stand. All 7533 trees were measured for dbh and a subset of 30 trees in each of the 48 treatment plots were measured for height. The dry biomass of each sample tree was estimated by wet weighing and then dry weighing randomly selected subsamples of tree components. Allometric models were used to estimate stand biomass based on the 7533 dbh measurements. Forest Floor (FF) was sampled by compositing organic matter 5 cm was sampled along 3 randomly located 15 m x.3 m transects in each of the 48 treatment plots. Samples were ranked by decay classes of 1-5, with 5 representing the most advanced stage of decay. Soil cores were taken to depth of 91.5 cm at 2 randomly located subplots per 48 plots, and then the samples were separated by horizon and depth interval. Understory was sampled from 5 randomly located 2 m radius circular subplots in 48 equal-area treatment plots. Results and Discussion Estimated pools for the preharvest forest system Douglas-firWestern hemlock The bole and needles of live trees contributed the most N from the live tree proportion of the system. The largest pool of N was contained in the soil to 91.9 cm depth as is expected at a high productivity site in the Pacific Northwest. The second largest N pool at the site was in tree boles. The A horizon contained the greatest proportion of N of the soil horizons sampled. Live Tree Component kg dry biomass/ha kg C/hakg N/hakg dry biomass/ha kg C/hakg N/ha Needles44002335895100263973 Live Branches1780088524611500561017 Dead Branches9200446318370018283 Bole wood182200889011401262006172493 Bark20600106878312100606842 Total live above- ground 235000118426138716000079682667 Standing dead trees 26021241519499304 Snags6687328321302414859 Total dead Above-ground 92894524264973241513 Total live and dead above- ground 244289122950141316497382097680 System Componentkg dry biomass/hakg C/hakg N/ha total live and dead above-ground for both tree species4092622050472093 understory221955 forest floor 5 cm14300072000309 Soil 0-15.7 cm (A)~184980924903855 -25.7 cm (B1)~89802449012241 -45.7 cm (B2)~138676693383693 -65.7 cm (B3)~84474422372668 -91.9 cm (B4)~85758428792984 total soil 0-91.9 cm~58369029184515441 total site (12.24 hectares)~99295259613718301