DIGITAL IMAGE ANALYSIS APPLIED TO SOIL PROFILES FOR ESTIMATING TREE ROOT BIOMASS

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Abstract
We excavated 66 0.3-m3 soil monoliths and sieved them for aspen (Populus tremuloides) large root biomass (0.3 to 3.0 cm diameter). Equal numbers of these monoliths were located in 10-, 20-, and 32-yr-old stands. Prior to sieving, a 0.6-m2 profile face of each soil monolith was groomed vertically, sprayed with Rhodamine WT dye, and photographed with color infrared film. Digital image analysis of the resulting 35-mm slides successfully discriminated roots from soil and rocks, but was unable to sort tree roots from the roots of understory species. The total cross-sectional area of aspen roots visible in the soil profile and the biomass of aspen roots in the associated soil monolith were correlated (r = 0.64); both declined with increasing stand age. The frequency of aspen roots in a profile face was poorly related to root biomass.