The regeneration of Eucalyptus regnans F. Muell. under retained overwood: seedling growth and density

Abstract

The native Eucalyptus regnans forests of South East Australia are managed for multiple use, including wood production. The primary silvicultural system used for wood production is clearfelling. Some criticisms of clearfelling concern differences between the resulting stand structure and that following wildfire, particularly in relation to the frequency and distribution of both living and dead hollow bearing trees. The Victorian Silvicultural Systems Project is evaluating the potential of alternative systems to clearfelling, including the retention of live overwood, either permanently or temporarily. This study examines the establishment and early growth of E. regnans under increasing levels of overwood retention. Retained overwood had a strong negative effect on seedling growth, vigour and density, even at low retention levels. The pattern of height and diameter growth suppression at three years was almost linear, with height and diameter under full overwood retention (40–45 m 2/ha) being approximately 57% and 62% respectively of that observed under negligible overwood competition. Stem volume reduction of the order of 50% occurred by a retention level of 12 m 2/ha (ca. 20%). Seedling vigour, as indicated by the height to diameter ratio, was also strongly influenced by overwood retention. An increasing height to diameter ratio was observed as the overwood retention increased, with the trend accelerating at levels greater than about 20 m 2/ha. The density of seedlings in a dominant or co-dominant competitive position by three years reduced with increasing overwood competition, with the number of dominant and co-dominant seedlings under full overwood retention approximately 17% of that under negligible competition.