Summarised from an article by I C Boyer
Shining Gum (Eucalyptus nitens) has been promoted as the tree to provide us with a perpetual firewood supply. However, some are finding that around 40% of the cut stumps fail to regenerate. Some of this loss is due to harvesting technique, and taking a little more care will improve recovery rates, but the largest contributing factor lies in ‘the nature of the beast’ and even the most surgically precise harvesting cannot guarantee that regeneration will be satisfactory.
Good coppice regeneration depends on the tree having a good supply of buds beneath the bark which, when the foliage of the tree is removed, are freed of the dormancy forced on them by the dominance of the growing tips.
Eucalypts have evolved dormant buds to allow rapid regeneration after defoliation, usually through fire, and there are two types of such buds: epicormic (under the bark) and lignotuberous (woody, bulbous-rootlike). The first originates with the bud in a leaf axil which did not develop into a branch early in its life but remains waiting to be freed from apical dominance. On the other hand, lignotubers develop from cell division of the bud in the axils of the first one or two pairs of seedling leaves, which results in a swelling or outgrowth at the base of the trunk. Some eucalypts (such as E nitens) lack lignotubers, and must depend on the epicormic buds for regeneration. If the majority of the trunk has been removed as harvested firewood then so too have most of the epicormic buds on which the tree would normally depend. The capacity of the tree to regenerate then rests with the few remaining buds on the lower trunk and these sometimes fail for one reason or another, resulting in the death of the stump. This means that good management techniques are vital to obtain the best results from a relatively poor coppicer such as E. nitens.
There are three main aspects of the harvest which can impact upon the regeneration rate.
- Harvest timing. Cut the crop when the tree is actively growing so long as you allow sufficient time for shoots to grow and harden before the onset of winter. The larger the regeneration shoots by winter the better. However, if the harvesting is done too early in spring, regeneration may be too slow to provide sufficient energy for spring root growth. The best time, as far as the tree is concerned, is early summer when regeneration will be rapid and well-hardened by June.
- Felling. The higher the stump the more epicormic buds are available for regeneration. The cut should be made with a north-facing slope to facilitate drying. Avoid tearing the stump bark as this not only destroys dormant buds but allows water to collect at the bottom of the tear causing further damage. There is minimal danger of fungal attack on the stump and this can be limited further by careful cutting, or removal of any damaged trunk with a second, slanted cut, keeping the tip of the saw to the lowest side to minimise tearing the cut tissue. Application of a sealant such as acrylic paint or anti-fungal paint within 30 minutes of cutting will further decrease the risk of fungal attack.
- Removal of the harvest. Care should be taken to minimise bruising of the stumps during removal of the felled logs. Young eucalypt bark is not thick enough to prevent damage to the underlying buds if a log is dragged around a stump.
- The major attribute of E nitens for firewood is its tremendous early growth rate that few other species can match in the range of sites and climates in which nitens thrives. Although there are other species which are far superior coppicers, a change of species to a more reliable coppicer will often mean increasing rotation times or lower yields. If you choose to stick with E nitens for coppicing, attention to detail at harvest time will be well rewarded.
This article is reproduced with the kind permission of the New Zealand Tree Crops Association. For more information on useful tree crops - including nut and fruit trees, trees for shelter, timber, stock fodder and firewood - contact your local branch.