Loss of organic matter and carbon during slash burns in New Zealand exotic forests

The quantity of carbon lost to the atmosphere through volatilisation during burning of Pinus radiata D. Don and Pinus contorta Loudon forest logging slash was estimated from measurements made at four P. radiata sites and one P. contorta site in New Zealand. Pre- and post-burn fuel mass and carbon content were assessed at each site. On average 271 C/ha, or 62 % of carbon present before burning (excluding that contained in stumps, roots, and mineral soil), was lost to the atmosphere as a result of slash burns at the four P. radiata sites. AttheP. contorta site 33 tC/ha, or48 % of carbon present before burning (excluding that contained in stumps, roots, and mineral soil), was lost to the atmosphere as a result of slash burning. Duff (F and H horizons), litter (L horizon), and sound woody material exceeding 7 cm in diameter were the components that contributed most to this loss. Total carbon loss in New Zealand due to burning of plantation forest logging slash was estimated to be 10 300 tonnes/year (s.e. = 1800) for P. radiata and 1600 tonnes/year (s.e. = 1160) for P. contorta. Relationships between carbon loss from individual sites and the specific codes and indices of the Canadian Fire Weather Index System were examined. The best predictor of carbon loss was the Fire Weather Index itself. The development of a comprehensive system for modelling carbon losses from slash burns will require more information to develop a larger data set