Biomass – 01Preface


Biomass by diameter size classes of five understory coniferous tree species in southern Oregon was estimated using regression equations. Species included white fir (Abies concolor), Shasta red fir (Abies magnifica var. shastensis), lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa), and mountain hemlock (Teuga mertensiana). Trees ranged up to 3 m tall and were selected from “open” and “dense” overstory classes. Estimates of biomass, segregated into foliar, 0-0.63 cm live, 0.64-2.53 cm live, 2.54-7.61 cm live. 7.62-20.32 cm live, 0-0.63 cm dead, and 0.64-2.53 cm dead diameter size classes, were made using as independent variables groundline diameter, total height, diameter2 x ht, and basal area. Coefficients of determination (R2) were high, exceeding 95 percent for total biomass in every case. Coefficients of determination tended to be lower as diameter size class increased. Tree age was predicted much less precisely than biomass. A simplified procedure using tree height to predict biomass is presented for management application.

The author thanks the staff of Crater Lake National Park, particularly Dan Sholly and Mark Forbes, for coordinating space and field assistance on this project. The following people provided field and laboratory assistance: R. Scott Berg, Roberta Chapman, John Davis, Shannon Downey, Lora Isberg, and Robert Wagner. Major assistance in data analysis was provided by Robert Flewelling. Production of the publication was coordinated by Nadyne Snyder.


Forest fuel inventories have traditionally concentrated on dead and down fuels because these are the predominant classes of available fuel in most prescribed fires and many wildfires. However, low intensity prescribed fires can create as well as consume fuels, primarily by causing mortality of understory trees. The biomass and fuel size class distribution of understory trees are not well documented, although dead fuels created in initial fires can significantly affect the fire behavior of reburns. This report investigates the biomass of five common understory trees in southern Oregon. The study objectives were to: 1) determine biomass of several species of understory trees by diameter size classes; and 2) relate the measured biomass values to easily measured tree characteristics.

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