Long-term growth of Phytophthora cinnamomi tolerant species of eucalypts planted on sites of varying dieback hazard in Gippsland.  M. T. Lutze.  November 1998.  24pp. (unpubl.)

SUMMARY

A number of studies were commenced during the 1970s to investigate procedures for rehabilitating Phytophthora cinnamomi-infested sites. An experiment was established in 1973 to provide information on long-term growth of P. cinnamomi-tolerant tree species planted on sites of varying dieback hazard.

Four sites of varying P. cinnamomi disease hazard were selected for planting in Gippsland. Six eucalypt species of moderate to high expected tolerance of P. cinnamomi were planted in winter 1973. The species were Eucalyptus globulus ssp. globulus and ssp. pseudoglobulus, E. maculata, E. camaldulensis, E. viminalis, E. cladocalyx and E. saligna. E. sieberi and Pinus radiata were also included in the trial as controls, because their level of tolerance to P. cinnamomi were well known. Each site was completely cleared of all previously cut-over vegetation, and the residue pushed into windrows. Discing to a depth of 15-25 cm followed the clearing and rough heaping. All plots except Yarram were fenced with wire netting and strands of plain and barbed wire. Yarram had a wire mesh fence which did not prevent rabbits from entering the enclosure.

Plots were measured at about one month after planting, and at age 1 and 2 years (height), and 3, 5, 7 and 21 years (height and diameter).

It was found that:

• Mortality of the high susceptibility species ( sieberi) increased with increasing hazard. However mortality of this species could be partly attributed to poor planting stock.
• Mortality generally occurred during the first three years after planting which coincided with the period of stand development when cinnamomi activity is likely to be greatest.
• Seasonal rainfall patterns during the first three years after planting were generally not conducive to great expression of cinnamomi dieback and P. cinnamomi-related mortality was probably relatively low, particularly at the lower hazard sites.
• Growth rates of sieberi, compared to other species, decreased with increasing site hazard, whereas growth rate of E. maculata and E. saligna, compared to other species, tended to increase with increasing site hazard, particularly from age 7 to 21. Growth rates of the moderately tolerant species (P. radiata) and the resistant species (E. camaldulensis) did not respond to varying site hazard in a predictable way.
• The results of this trial with low-intensity silvicultural inputs differ from those in very fast-grown plantations with more intensive silvicultural treatments, and perhaps are more indicative of species selection for slower-grown plantations for sawlog production.

Recommendations are made concerning further research and development into species selection and silvicultural practices applicable to growing sawlogs in plantations on sites of varying Phytophthora cinnamomi infestation in the lowland forests of Gippsland.