Biomass and production of fine and coarse roots during regrowth of a disturbed subtropical humid forest in north-east India

Seasonal variation and depthwise distribution of dry matter in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in three stands of a subtropical humid forest of north-east India representing different stages of regrowth after tree cutting. The mean annual standing crop of fine (<2 mm in diameter) and coarse (2-15 mm diameter) roots increased gradually from 5.4 Mg ha(-1) and 0.7 Mg ha(-1) in 7-yr old regrowth to 9.4 Mg ha(-1) and 2.8 Mg ha(-1) in 16-yr old regrowth, respectively. The contribution of fine roots to the total root mass declined from 88% in 7-yr old regrowth to 77% in both 13 and 16-yr old regrowths, while that of coarse roots increased from 12 to 23%. A major portion of fine roots (59-62%) was present in 0-10 cm soil layer, but the coarse roots were concentrated in 10-20 cm soil depth (38-48%). In ail the three stands, biomass of both fine and coarse roots followed a unimodal growth curve by showing a gradual increase from spring/pre-rainy season to autumn/post-rainy season. Biomass to necromass ratio increased from 2.5 in the 7-yr old to 3.2 in the 16-yr old stand. The annual fine root production increased from 5.9 Mg ha(-1) to 7.7 Mg ha(-1) and total root production from 7.6 Mg ha(-1) to 14.7 Mg ha(-1) from 7-yr to 16-yr old regrowth.