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

Biomass quantities at three different sites in tropical moist mixed seconda ry deciduous forests before and after burning have been quantified in the f orest patches cleared for shifting cultivation purposes. The main objective of the experiments was to study the spatial variability in the amount of b iomass burnt and the contribution of different components viz., bore, branc h, and mixed leaf litter in the burning process affecting the combustion fa ctors. Species composition at the three sires varied with respect to each o ther. The total density of species before burning at the three sites for mo re than 10 cm diameter were found to be 3192 (site 1), 1194 (site 2) and 14 44 (site 3) stems/area, respectively. Analysis of the results from girth-cl ass and density relationships suggests that nearly 80% of the stems occurre d in the range from 10-40 cm girth for site one, 64.2% in 10-55 cm girth cl ass 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. T he 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 valu e of 2566 kJ s(-1) m(-1) reported for savanna fires. The individual combust ion 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 h aving the highest (84%). The contribution of dry biomass material having mo re than 70 cm diameter is found to be very low indicating that most of the trunks were burnt superficially. The overall combustion completeness sugges ted that mixed leaf litter and branch material contributed to most of the c ombustion. Of all the three sites, site three had been found to be having h ighest 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. (C) 2001 Elsevier Science Ltd. All rights reserved.