The paper reports on an investigation into potential causes of dieback of mature River Red Gum trees located on Malcolm Creek, Craigieburn and possible management responses. The health of these trees may have been affected by changes in the hydrology of the Malcolm Creek catchment following urban development.

Dieback is a well-known phenomenon in eucalypts, with multiple biotic and physical factors reported to be implicated in such conditions. The investigation at Malcolm Creek was designed to assess the effects of:

- Changed water regime from urban development and stormwater management;
- Repeated cycles of defoliation by lerp insects and/or possums;
- Climatic conditions which may favour increased lerp insect populations;
- Senescence processes in mature or overmature trees.

A detailed assessment was undertaken of trees along a 1.2 km section of Malcolm Creek. Dieback was found to be severe in about 15-20% of those trees at the time of the assessment in January 2018. All of the most severely-affected trees were located along the bed of Malcolm Creek.

The investigation concluded that the dieback was most likely influenced by multiple factors, with the primary determinant being the prolonged waterlogging now being experienced trees growing in or adjacent to Malcolm Creek. This factor and favourable climate may also have predisposed the trees to repeated cycles of defoliation.

Rectifying the prolonged waterlogging of the trees, by changing stormwater drainage and management appears to be the key to protecting or restoring the health of mature River Red Gum trees along Malcolm Creek in the long-term.