Establishment of mixtures of eucalypt species on dieback forest sites in East Gippsland.  M. T. Lutze.  August 1999.  23 pp. (unpubl.)

SUMMARY

Crown dieback was observed to be increasing during the 1950s and 1960s in the lowland forests of East Gippsland and in 1969 Phytophthora cinnamomi (cinnamon fungus) was identified as the cause of eucalypt dieback. A trial was established in 1984 to determine whether long term rehabilitation of dieback-affected forest could be achieved by direct sowing of mixtures of local eucalypt species, tolerant and susceptible to P. cinnamomi. This paper reports the results of the study of regeneration processes and seedling establishment to 15 months after sowing.

Three sites, varying from light to heavy dieback severity, were cleared and burnt, then divided into six 100 m x 100 m 'superplots', three of which were sown with a mixture of between six and nine eucalypt species, indigenous to the site, and the other three were sown with a mixture of E. sieberi and E. globoidea, as controls. Observational plots of two types were covered at the time of sowing, then sown soon after, as follows:

• 'Random' plots - five randomly located plots within each superplot at each site sown with the same mix as the 'superplots' but at five times the rate.
• 'Species separated' plots - on the three indigenous mixture 'superplots' at each site one plot was located on an ashbed and another plot on disturbed soil; plots were divided into subplots and each of the species were sown onto these.

Both 'random' and 'species separated' plots were assessed on a monthly cycle from approximately two weeks after sowing in March-April 1984 until June 1985. Weather was also recorded for part of this period. Seedbeds were assessed on 'random' plots soon after slash-burning.

It was found that:

• Germination occurred in autumn and early winter which is consistent with the generally moderate temperature and adequate rainfall during that period. Most mortality occurred approximately two months after germination and during the spring immediately following sowing. Germination and seedling percents varied with species and site.
• In general the least germination and seedling percents were obtained for the species with highest cinnamomi susceptibility, and greatest germination and seedling percents were obtained for the species with highest P. cinnamomi resistance. However inconsistent ranking of some species on some seedbed types suggested that other factors such as burning intensity and soil drainage may have affected regeneration and survival.
• The seedling percent results indicated that there were sufficient established seedlings of most species to satisfy regeneration criteria but the degree of performance varied with seedbed and site. Autumn germinants of all species dominated the regeneration in terms of quantity and height at 15 months after sowing. Survival, growth and the number of established seedlings increased with site burning intensity and soil depth.
• Species composition of established seedlings closely matched the species composition of sown seed. The differences between sown and seedling composition were probably only significant for tricarpa, which occurred at greater than the sown composition at two sites.
• All species indigenous to the sites, including cinnamomi susceptible and resistant species, could be established on the range of seedbeds provided through the clearing, slash-burning and sowing treatments applied.
• The results for a number of species with marginal regeneration performance at the sites of moderate to high dieback severity could be improved if higher intensity burning was used to increase the percentage of moderate intensity burnt seedbed and decrease the percentage of disturbed soil seedbed. The results could be less satisfactory in years when climatic conditions favour dieback.

Recommendations are made about further monitoring and analysis of the trial, and the application of the results to operational practice.