Distribution and development of dieback in the Grampians.  B. K. Ward, F. K. Kassaby and I. Christie.  March 1978.  27 pp. (unpubl.)

SUMMARY

This report describes the distribution and extent of dieback in the Grampians State Forest. The distribution of Phytophthora cinnamomi is given and vegetative, physiological and climatic factors are related to dieback and P. cinnamomi.

Aerial reconnaissance and mapping of dieback patches was used as a basis for surveys. Between October 1975 and May 1976, about 60% of the Grampians was surveyed on the ground. The remaining area was not checked due mainly to access difficulty. However the area surveyed was considered to be representative of dieback patches found during aerial reconnaissance, vegetation types, land forms and topographic positions. Dieback patches were assessed for area, severity, estimated time since the onset of dieback, vegetation affected, land systems, topography, utilisation, roading and fire history.

Over 2 000 ha of the ground survey area was visibly affected. Dieback was concentrated in those areas characterised by shorter dry sclerophyll forests (6-21 m) and low woodlands that are relatively flat (0 - 2°slope) and have northerly to easterly aspects. Dieback was also concentrated on the outwash slopes of the Victoria and Mt Difficult Ranges. Based on the above characteristics 65 000 ha (30%) of the Grampians State Forest was considered susceptible to dieback.

Examination of past aerial photographs of parts of the Grampians show that dieback of a noticeable magnitude probably started during the 1950’s.

The severity and extent of dieback patches appears to be related to P. cinnamomi, weather patterns and fire. Analysis of weather records for the Grampians seems to indicate that dieback epidemics occur during severe summer or autumn drought periods preceded by above average spring or summer rainfall. The burning of sites showing signs of dieback was associated with a significant increase in severity of dieback. About 4.4 percent of the total number of native plant species, including four endemic species, recorded in the Grampians appear to be susceptible.