Biomass, Litterfall and Changes in the Soil Properties as Influenced by Age and Tree Density in Alnus nepalensis D. Don

Abstract

Biomass production and soil properties of rhizosphere in age sequences from seedling to a mature tree and the effects of tree densities (625 to 10,000 trees ha^-1) on morphological characters, biomass, litterfall and soil properties were studied in Alnus nepalensis at an altitude of 1250 meter from mean sea level in North-Eastern Hilly Region. Allometric relationships were developed for estimating biomass and litterfall on basal diameter/tree densities. Linear equation of log 10 biomass =A+8 log 10 basal diameter/tree density were found to be the best fit to describe more than 91-98% variation in age sequence and due to tree density but only 67-71 % variation could be accounted in case of biomass productivity and litterfall, In age sequences, per cent dry matter in whole plant varied from 23 to 66% and contribution of leaf (34 to 9%) and root (48 to 7%) decreased to total biomass as the plant grew older. The contribution of stem increased from 18 to 84%. In rhizosphere soil, organic matter increased up to 8.0 cm basal diameter of the plant but a drop of 1.7 unit in soil pH was recorded as seedlings grew to a mature trees. Plant height was maximum under the stand of 10,000 tree ha^-1 but the diameters (basal and at breast height) decreased with increasing tree density, resulting into low tapering rate of the boles. With increasing tree density, biomass per tree and the contribution of leaf and branch to total biomass decreased but the biomass productivity was highest (87 t ha^-1) at 4444 trees ha^-1 in fifth year after planting. Litter yield increased with increasing tree density during second to fourth year but in fifty year, 625 trees ha^-1 gave highest litter yield and its nitrogen content, resulting into 518 kg N ha^-1 in the floor litter. Soil pH , exchangeable K, Ca+Mg decreased but organic matter and available P increased under the stand of 2,500 to 10,000 trees ha^-1 during five years.