Fuel characteristics, low intensity burning and loss of carbonduring regeneration burning in Eucalyptus obliqua wet forestat the Warra LTER site

摘要

Eucalyptus obliqua wet forest fuel characteristics and burning were at the Warra Long Term Ecological Research (LTER) site in Tasmania’s Southern Forests. The study examined pre-logging, post-logging and post-burning variation in fuel characteristics in wet sclerophyll and mixed forest. The utility of low intensity burning in coupes with dispersed 10% of their overstorey retained was also studied. Mean near-surface fine fuel load in unlogged E. obliqua wet forest varied from 13 t ha-1 in mixed forest to 20 t ha-1 in wet sclerophyll forest. These fuel loads increased to between about 40 and 85 t ha-1 following logging. High intensity regeneration burns removed the majority of the fine fuel. In low intensity burns the amount of fuel removal was dependent on the fuel moisture. Two low intensity burns removed 50-90% of the fine fuel and required significantly higher numbers of personnel than high intensity burns. Low intensity burns were lit in mid to late autumn when fuel moistures are higher than in late summer/ early autumn when high intensity burns are normally performed. Although it was possible to perform low intensity burns in E. obliqua wet forest, their effectiveness needs to be assessed by forest managers. Factors influencing the planning of low intensity burns include the amount of ash bed required for eucalypt regeneration, the desired reduction in fire risk, the resources needed to perform the burn and the number of burns needed. After the initial study was concentrated on fine fuels, in 1998, it was decided to include all biomass on site in the study. By then, logging began or was completed (WR001B) in all four coupes so only pre-burning and postburning sampling of the total biomass were conducted in three remaining coupes.. In wet eucalypt forests, controlled regeneration burning is used to expose the seedbed for regeneration of eucalypts following harvesting. Controlled regeneration burning acts to remove forest litter, bark and branches from the forest floor and heats the soil to provide better germination conditions. However, combustion of organic matter leads to the release of carbon dioxide (CO2) into the atmosphere. Little work has been done on the effect of slash burning on carbon emissions to the atmosphere. If a significant amount of carbon is lost annually as a consequence of controlled regeneration burns, this practice should be taken into account when calculating carbon sequestration for Australian forests. The results from this study show that 52-63% of the total weight of organic material and its carbon content was lost to the atmosphere during burning. The majority of carbon loss was from slash greater than 7.0 cm in diameter.