Soil and nutrient processes related to eucalypt forest dieback

Summary

Crown dieback is occurring in extensive areas of eucalypt forest in east coast Australia. While there is variation across sites and species with regard to the rate and intensity of the development of dieback, there are indications of common causative factors. Water stress tends to exacerbate dieback but there is no evidence that it is a primary cause. Evidence indicates that nutrients are a primary factor. Nutrient depletion from soils through the process of immobilisation in biomass as a stand grows has been suggested as a cause, but there is no evidence for this hypothesis. There is evidence of long-term accumulation of nitrogen (total and available) in undisturbed stands, and this leads to nutrient and biochemical imbalances in the foliage together with root morphological changes. Biochemical changes include increases and imbalances in amino acids resulting in the foliage being more attractive to folivores. and consequent increased herbivory. The level of insects or other folivores is a symptom of the problem and not a primary cause of dieback. Regular burning maintains reasonably stable levels of nitrogen within the system and these levels are the long-term norm for many eucalypt ecosystems. Essentially, lack of regular low-intensity burning can lead to reduced stand health and growth, and, in the longer term, changes in stand structure.

Keywords:

• nitrogen
• nutrition
• nutrient cycling
• hebivores
• Eucalyptus
• Australia