Biomass and combustion characteristics of secondary mixed deciduous forests in Eastern Ghats of India

Abstract

Biomass quantities at three different sites in tropical moist mixed secondary deciduous forests before and after burning have been quantified in the forest patches cleared for shifting cultivation purposes. The main objective of the experiments was to study the spatial variability in the amount of biomass burnt and the contribution of different components viz., bole, branch, and mixed leaf litter in the burning process affecting the combustion factors. Species composition at the three sites varied with respect to each other. The total density of species before burning at the three sites for more than 10 cm diameter were found to be 3192 (site 1), 1194 (site 2) and 1444 (site 3) stems/area, respectively. Analysis of the results from girth-class and density relationships suggests that nearly 80% of the stems occurred in the range from 10–40 cm girth for site one, 64.2% in 10–55 cm girth class for the site two and more than 80% of stems in 10–40 cm girth class for the site three, indicating very poor and secondary nature of the forest. The fire intensity is found to be high for site one with 60 847 kJ s^-1 m^-1, when compared to 31 086 and 42 789 kJ s^-1 m^-1 for second and third sites, respectively. The values are comparatively higher than the mean value of 2566 kJ s^-1 m^-1 reported for savanna fires. The individual combustion completeness suggested that among the different components of biomass, branch material with less than 10 cm and upto 5 cm dbh contributed to more than 60% of combustion. Mixed leaf litter contributed to about more than 50% of individual combustion completeness at all the sites, with third site having the highest (84%). The contribution of dry biomass material having more than 70 cm diameter is found to be very low indicating that most of the trunks were burnt superficially. The overall combustion completeness suggested that mixed leaf litter and branch material contributed to most of the combustion. Of all the three sites, site three had been found to be having highest combustion completeness of about 30.04% when compared to 20.18% and 16.1% for first and second sites, respectively. In the study, comparison of combustion factors for different vegetation types has also been made.