Burning outcomes following aggregated retention harvesting in old-growth wet eucalypt forests

Abstract

In Tasmania, Australia, aggregated retention (ARN1Abbreviations: ARN, aggregated retention; CBS, clearfell, burn and sow.1) is being implemented as an alternative to clearfelling in old-growth wet eucalypt forests. These forests have traditionally been regenerated using a high-intensity burn and aerial sowing, but the use of more complex harvesting designs makes conventional high-intensity burning difficult. In 2007, a new burning method (‘slow burning’) was developed specifically for ARN coupes. This paper compares site preparation, burning weather conditions and burning outcomes in ARN and conventional clearfell, burn and sow (CBS) coupes burnt from 2007 to 2010. ARN coupes had higher perimeter-to-area ratios than paired CBS coupes, and 8% more of the harvested area was affected by firebreaks. Although there was less burnt seedbed and more compacted seedbed in ARN coupes compared to clearfelled coupes, mean levels of receptive seedbed were adequate and are unlikely to limit regeneration success. Burn impact on unharvested forest was greater in ARN coupes, due largely to burning in the retained aggregates. Despite this, only 11% of aggregate area was burnt overall, and the current guidelines for aggregate size (most >1ha) appear sufficient to keep burn impact within acceptable thresholds. Firebreaks affected from 4–32% of the harvested area in the coupes measured in this study, and were 10m wide on average, twice the required width. To reduce soil disturbance and potential impacts on regeneration, firebreaks should be established only where absolutely necessary, and firebreak widths should be minimised wherever possible.