Five age series stands ofAlnus nepalensis D. Don monocultures have been selected from the Pankhasari range of the Kalimpong forest division in the Eastern Himalayas. Chemical soil propeties such as organic carbon, total nitrogen, C∶N ratio, available phosphorus and exchangeable cations (Ca+2, K+ and Na+) were analysed in all these different ages of plantation stands from the surface to 1 m deep profiles to find out the long term effect ofA. nepalensis on the soil quality of these erosion vulnerable slopes. Organic carbon, available phosphorus and total nitrogen content per-hectare increased with increasing plantation stand age. Analysis of variance for nutrients showed significant variation in depth (total nitrogenP<0.001; organic carbon,P<0.001; available phosphorus,P<0.05; exchangeable Ca+2,P<0.01; and exchangeable K+,P<0.01) and between plantation stands (organic carbon,P<0.05; and available phosphorusP<0.05). High value of total nitrogen content (34.97t ha−1) was obtained in 46 yr old stand. Soil pH is low. It increased down the depth and in older plantations. These stands with high soil total nitrogen and organic carbon content show increased fertility of the stands. The cover ofA. nepalensis in rocky, landslide and ecosion prone slopes of the Eastern Himalayas, serves to protect and improve soil quality.
