Windthrow in Tasmania, Australia: Monitoring, prediction and management

Abstract

In Tasmania, Australia, native hardwood production forests (Eucalyptus spp.) are managed increasingly under variable retention harvesting systems alongside more traditional clearfell (clearcut), burn and sow regimes. To augment timber supplies, a plantation estate (Eucalyptus spp. and Pinus radiata) is managed intensively for pulp and sawlogs. Situated between latitudes 40° and 44° south, the 'roaring 40's', where strong winds and heavy rainfalls prevail, Tasmania is characterized by coastal zones, open plains and mountainous terrain. Soil physical properties vary markedly; shallow stony soils of low mechanical strength or those characterized by poor drainage are common. The resulting climatic, site and silvicultural conditions have meant that foresters must address the issue of wind disturbance. This includes damage to native forest aggregates and associated understorey species, or windthrow occurring in native regrowth and plantation forests subsequent to intensive thinning operations. In addition, there is growing interest in the relationship between exposure, stem form and wood quality. This paper provides a summary of progress made towards monitoring, prediction and management of windthrow in Tasmania. Aerial health surveillance protocols now ensure that windthrow events are adequately characterized to provide records against which to validate predictive modelling techniques. Pilot monitoring schemes have demonstrated that wind damage associated with variable retention silviculture in the native forests has not reached significant levels. Similarly, windthrow associated with production thinning of plantation forests has only affected a small proportion of the estate. A risk assessment procedure for Tasmania's plantation forests, WindRISK, has been developed. This combines a GIS-based assessment of topographic exposure with a field-based assessment of other key variables. Other approaches such as LiDAR (light Detecting and Ranging) or airborne laser scanning show great potential. Wind-tree relationships and the implications for stem form, wood properties and lumber recovery in eucalypt species are also discussed. © Institute of Chartered Foresters, 2008. All rights reserved.