A study of the natural regeneration of mixed eucalypts under partial cutting conditions in Wombat Forest.  R.O. Squire and J.G. Edgar.  February 1975.  25 pp. (unpubl.)

SUMMARY

Results are reported of a trial established* in 1969 to study aspects of the natural regeneration of mature eucalypt stands (predominantly E. obliqua) in the Select Hardwood Working Circle of the Wombat State Forest. The trial was designed to test regeneration options under conditions more compatible with multiple-use objectives than already proven techniques which make use of extensive clear-cutting and/or high intensity slash burning for the preparation of adequately receptive seed-beds.

In this trial, regeneration was studied in strips, 20 metres and 40 metres in width (with replicates orientated to receive maximum and minimum afternoon sunlight); in large (40 metre) and small (20 metre) gaps; and in uniformly thinned stands with 18, 14 and 9 sq. metres of retained overwood per hectare (80, 60, and 40 sq. ft. per acre).

Disturbed seed-beds were prepared by logging, and slash disposal was by fuel reduction methods in the spring of 1969. There was strong evidence that disturbed mineral soil is an adequately receptive seed-bed. Concentration of logging within the felled strips provided such a seed-bed which for two years, was adequate in both quantity and distribution. Deep ripping was applied to a number of cleared strips in February, 1971 as an additional seed-bed treatment.

Results indicate that, in this study area, the reserve of lignotubers was insufficient to assure reliable regeneration. Accordingly, a significant seedling contribution was generally necessary to achieve satisfactory stocking. Seedling regeneration was best in large openings (strips of 40 metres width and gaps of 40 metres diameter). However, there was strong evidence that, with deep ripping, satisfactory regeneration can be obtained in strips down to 20 metres in width. Regeneration in strips was further improved by varying strip orientation according to the time of seed-bed preparation viz: for spring preparation, orientate strips to receive minimum afternoon insolation, and for late summer-autumn preparation, orientate strips to receive maximum afternoon insolation. In uniformly thinned stands, overwood in excess of 11.5 sq. metres per hectare (50 ft²/ac) was found likely to inhibit seedling establishment and special attention needs to be given to the provision of an adequate seed-bed if seedling regeneration is to be successful.

Where seedling regeneration in association with partial cutting must be relied upon, it is necessary to pay particular attention to three conditions:

1. overwood retention/ proximity,
2. seed supply,
3. seed-bed receptivity.

Overwood competition is like to be of primary importance, and become limiting where:

1. overwood is closer than 20 metres,
2. overwood basal area exceeds 11.5 m²/ha (50 ft²/ac).

*Designed and established by J.G. Edgar