Root biomass studies of old-growth Douglas-fir

Root biomass studies were conducted in an old-growth stand ofconifers in the western Cascades of Oregon. The root systems of threeDouglas-firs (Pseudotsuga menziesii var. menziesii (Mirb. ) Franco)with diameters at breast height of 94, 110, and 135 cm were excavatedand weighed to provide a basis for regression equations for estimatingthe biomass of roots larger than 10 mm in diameter in the stand. Thebiomass of small roots was estimated from soil core samples takenwithin the stand. The total root biomass in the stand sampled wasestimated as 210 t/ha. The contribution of small roots to this totalamount was estimated as 11.3 t/ha.
Nutrient analyses were performed on root samples from both theexcavated root systems and the soil cores. Results were used for pro-jecting the nutrient capital contained in the roots of the old-growthstand.
with results of the present study. A double logarithmic plot of rootsystem biomass on stem diameter at breast height shows a linearrelationship. Closer examination suggests that the variation in the rootsystem biomass to diameter relationship within a given species iscomparable to the variation between different species. Fine rootbiomass, estimated as 9. 7 t/ha, falls within the range of values foundby other investigators.