ROOT BIOMASS DISTRIBUTION IN A MOIST TROPICAL MONTANE FOREST

Root biomass was measured in the soil and canopy of a tropical montane forest in Costa Rica. Below-ground total root biomass in the soil of this forest ran ed from 1600 g m-2 to 7200 g m-2 and biomass of fine roots (<2 mm diam.) ranged from 300 g m-2 to 1300 g m-2, depending on slope position. A root mat was present on thc forest floor which contained 50 to 70% of the below-ground fine root biomass. A similar estimate was obtained for fine root biomass in the forest floor (H + A1 horizons) using both soil cores (10 cm diam. n = 15) and excavated soil pits (1 m-2, n = 4). About 5% of the below-ground fine roots and 13% of the below-ground total root biomass resided in the B2 horizon, which extended from 85 to 185 cm below the forest floor surface. Root biomass on surfaces of inner branches and at branch junctions within the upper canopy of mature trees totaled 72 g m-2 forest floor area. Fine root biomass (<2 mm) in the canopy comprised about 45% of total canopy root biomass and about 5% of the below-ground fine root biomass. About 800% of canopy root biomass was found at branch junctions. The fine root density in canopy humus accumulated at these junctions was about 20% higher than that found in the forest floor humus layer, resulting in a potentially effective system for exploiting stemflow nutrient inputs. Root biomass in the canopy could be important in conserving nutrients mineralized from canopy humus, and those entering this forest in mist and rain.