Early regeneration results following aggregated retention harvesting of wet eucalypt forests in Tasmania, Australia

Abstract

Aggregated retention (ARN) harvesting has been adopted as an alternative to clearfelling in most of Tasmania’s wet eucalypt forests, although the effects of this silvicultural system on regeneration establishment and growth were still uncertain when this decision was made. To address this knowledge gap, eucalypt regeneration was assessed in 31 operational ARN coupes and 31 paired clearfell, burn and sow (CBS) coupes established from 2007 to 2010. There was no difference in eucalypt seedling stocking, density or height between ARN and CBS coupes at 1year of age. At 3years of age, seedling density and height did not vary with silvicultural system, and stocking was only 5% lower in ARN coupes when two outliers were removed. This early regeneration success in the ARN coupes is attributed to the high availability of receptive seedbed achieved in the broadcast burns on these coupes, the adoption of aerial sowing as a standard operating procedure, and to the absence of any increase in browsing pressure or edge-related growth suppression. Although the proportion of the harvested area within one tree height of standing forest (i.e., under ‘forest influence’) was 34% higher in ARN coupes compared to CBS coupes, there was no evidence of suppression of regeneration by the standing forest edge at 3years of age. Seedling height and density were strongly related to the state of the seedbed, and increased with increasing burn intensity. Seedling density increased by an average of 1700sph in both ARN and CBS coupes between the ages of 1 and 3years, but despite this ongoing recruitment, 24% of coupes had low seedling densities at age 3years and a review of sowing rates is recommended. This study confirms that the creation of burnt seedbed is essential for good early regeneration in wet eucalypt forests, and indicates that regeneration can be just as successful after aggregated retention harvesting as after clearfelling, so long as stands are managed appropriately.