Spatial analysis of eucalypt dieback at Coranderrk, Australia

The cause of tree disease in any location is difficult to diagnose because of the multiplicity of potential causes. Spatial analysis provides useful evidence on the significance, scale and shape of patterns for disease diagnosis. This study explores the causes of dieback through spatial analysis of tree health at Coranderrk Reserve, an example of an important conservation reserve on the urban fringe of Melbourne, Victoria. Ca. 200 trees were sampled at two sites and measured for position, diameter and height in each of two different community types. An index of tree health was developed, and each tree was assigned a value of health. Dead trees were categorized based on state of decay. Correlograms using Moran's I found significant spatial stucture at both study sites. The study employed a method of analysis that compares the spatial patterns in dead and living trees. When all dead trees were eliminated from the analysis, significant spatial pattern was found only at one site, The spatial structures obtained were compared with those expected from the different possible causes of tree dieback. Some potential explanations were eliminated. The results illustrate how spatial analysis may make useful contributions to disease diagnosis if employed systematically together with other modes of investigation.