Seedcrop development in Eucalyptus viminalis in high elevation mixed species forest of East Gippsland.  G. M. Dooley, M. D. Murray, M. T. Lutze, G. J. McCarthy and P. C. Perry.  March 2008.  18pp. (unpubl.)

SUMMARY

The seedcrop development cycle of Eucalyptus viminalis (manna gum) was studied at one site in the High Elevation Mixed Species forests of East Gippsland for a period of six years.

Seed traps were used to make sample collections of reproductive components, and the following stages of the seedcrop development cycle were identified:

• Inflorescence bud development
• Bract fall and umbel bud development
• Flowering and capsule and seed maturation
• Seed fall and capsule fall

The timing of reproductive stages during the cycle (see Fig. 3) was very consistent :

Seedcrop development occurred over a period of approximately 2.25 years, from bud initiation to seed maturation in capsules.

Quantities produced, and lost, of reproductive components were seasonally variable. For example, numbers of umbellate buds produced ranged from 2.4 million to 19.6 million per hectare, and mature capsules produced ranged from 0 in 2005 to 7.7 million in 2004. Percentage losses of inflorescence buds (generally 20-40%) and flowers (generally 40-60%) were fairly consistent over most years. Generally, a large quantity of inflorescence buds resulted in heavy seedcrops. A heavy seedcrop cycle was followed by a low seedcrop cycle for the period of the study.

Seedfall occurred through every month of the year with the peak fall occurring in February-April, which was only 2-4 months after seed maturation in the capsules.

Rainfall and temperature from a weather station near the site indicated that high summer rainfall may have been the cause for high losses of flowers and maturing capsules. Neither heavy snowfall and strong wind events, nor insect and bird predation, appeared to affect the numbers of reproductive components to any great extent.

Recommendations to assist in silvicultural planning:

• Undertake aerial surveys to detect flowering and use seed trap collections to predict the size and timing of potential seedcrops.
• Where seedcrops are moderate to heavy, harvest and regenerate coupes using the seed tree system, with slash-burning by mid-March.
• When collecting seed, start collecting capsules soon after capsule maturity (February - March) before natural seedfall becomes significant.