Spatial analysis of area and carbon stock in Populus deltoides based agroforestry systems in Punjab state, India

Abstract

Populus deltoides (Poplar) trees are widely grown on agricultural lands as boundary, block and agrisilviculture systems by farmers in the Indo-gangetic region including Punjab state in India. This species is preferred because of its short rotation and demand of wood for paper, plywood and matchstick industries. These Poplar based agroforestry systems play significant role in sequestration of atmospheric CO2 for a rotation of 6-7 years. In the present study, spatial analysis of Populus deltoides based systems for area, biomass and carbon stock has been done in Punjab using field data and remote sensing techniques. Four districts of Punjab state namely Hoshiarpur, Ludhiana, Rupnagar and Shahid Bhagat Singh Nagar were surveyed during Aug. 2018 and data on age, system, spacing, diameter at breast height and GPS points were collected from farmers’ fields. Agroforestry plots were also tracked with the help of GPS, which was used for identification and generation of spectral signature for Poplar species. High resolution LISS IV data (spatial resolution- 5.8m) of selected districts was processed and analyzed for mapping of Poplar based systems and estimation of area. Object oriented image classification technique was applied for identification and mapping of trees on farmlands. For this purpose, Object based image analysis (OBIA) module of ERDAS Imagine software was used (ERDAS 2009). Stem and aboveground biomass for Poplar trees of different ages were computed using developed biomass equations (Rizvi et al. 2008, Puri et al. 2002). The total biomass was derived by considering 79% of total biomass as aboveground biomass. Carbon stock (CS) was then calculated by formula CS = C x B; where C- carbon content (45.4%) and B - biomass (kg/ tree). In literature carbon content in poplar wood is estimated to 45.4 percent (Negi et al. 2003). Accordingly per tree biomass and carbon was converted into per ha biomass and carbon after multiplying with number of trees per ha. Results revealed that tree density ranged from 200 to 1905 trees ha-1 in the four districts. Stem and aboveground biomass ranged from 28.36-241.73 t ha-1 and 31.62-286.07 t ha-1, respectively. Estimated carbon stock in stem biomass and total biomass ranged from 5.58- 79.80 t ha-1 and 10.93-156.48 t ha-1, respectively. Area under Poplar based systems in Ludhiana, Shahid Bhagat Singh Nagar, Rupnagar and Hoshiarpur districts was estimated to be 3698.7, 534.0, 5465.2, and 10573.1 ha, respectively with more than 85 percent accuracy. Highest area under Poplar based systems was found in Rupnagar district, which is 57.4 percent of total agroforestry area. Study concluded that Populus deltoides based systems not only occupy sizeable area in selected districts but also contributing significantly towards carbon sequestration. Object oriented image analysis together with high resolution remote sensing data proved to be better technique for accurate mapping of trees on farmlands