The effects of slash burning on the mortality and collapse of trees retained on logged sites in south-eastern Australia

Trees may be retained on logged sites in eucalypt forests for a number of reasons, such as to provide wildlife habitat, for future wood production, for aesthetic reasons, to mitigate erosion, or to provide seed for regeneration. These trees may be required to survive for a considerable period to meet these objectives. Logged sites in eucalypt forests are routinely treated with a post-logging slash-burn to reduce fuel loads and facilitate regeneration. We compared rates of mortality and collapse among trees retained on logged sites that were routinely treated with a high-intensity slash-burn with logged sites routinely treated with a low-intensity slash-burn. All observations were made 2-5 years after logging. The proportion of all retained trees that were killed after logging was 37% on sites treated with a high-intensity slash-burn and 14% on sites treated with a low-intensity slash-burn. The rate of collapse among retained trees over the same period was 1.5 and 0.5%, respectively. Results of logistic regression models indicated that trees retained on logged sites were more likely to die and collapse if the site was treated with a high-intensity slash-burn; however, trees were also more likely to die if the basal area of trees retained on the site was relatively low and the site had a northerly aspect. Mortality was similar among all diameter classes on sites treated with a high-intensity slash-burn. Some of the objectives of retaining trees on logged sites, such as perpetuating hollow-bearing trees for wildlife, may be compromised where high-intensity post-logging slash-burns are employed.