Variation in Tree Density, Biomass and Carbon Stock with Altitude under the Large Cardamom-based Traditional Agroforestry System of Darjeeling

Abstract

It has been reported that the large cardamom-based traditional agroforestry systems in the Darjeeling Himalaya of West Bengal, India represents a sustainable land use system with a high potential to store and sequester biomass carbon. Therefore, the present study was undertaken to evaluate the changes in tree biomass stock and carbon accumulation of this indigenous system with altitude. The study area was classified into three altitude-classes as low (700–1200 m asl), mid (1200–1700 m asl) and high (> 1700 m asl). The tree biomass and carbon storage for low-, mid- and high-altitude classes was estimated at 630.17 and 296.18 Mg ha− 1, 397.05 and 186.61 Mg ha− 1 and 315.78 and 148.42 Mg ha− 1, respectively. Schima wallichi, Cryptomeria japonica and Cupressus cashmeriana were the most ecologically important tree species based on IVI (important value index) in the low-, mid-, and high-altitude classes, respectively. The IVI and total biomass of the five most ecologically important tree species in low-, mid- and high-altitude ranged from 17.34–26.04, 18.15–37.56, 27.13–42.43 and 9.05-133.75 Mg ha− 1, 1.38–37.43 Mg ha− 1 and 19.0-72.1 Mg ha− 1, respectively. Schima wallichi occurred in all the altitude-classes among the five most ecologically important tree species. In the study area, the average ecosystem carbon storage was estimated at 295.02 Mg ha− 1. The contribution of soil organic carbon to the ecosystem carbon stock increased with the increasing altitude. In contrast, the contribution of biomass carbon to the ecosystem carbon stock decreased with the increase in altitude. The ecosystem carbon stock estimated for the low-altitude class was 36.43% and 45.30% higher than the mid- and high-altitude agroforestry systems. The large cardamom-based agroforestry systems in the Darjeeling Himalayas are thus a prospective carbon sink, both in vegetation and soil due to higher tree densities and natural resource conservation-based traditional farming practices.