Seedcrop development in Eucalyptus viminalis in High-Elevation Mixed Species forest of East Gippsland

Summary

The seedcrop development cycle of Eucalyptus viminalis ssp. viminalis (manna gum) was studied at a site in the High-Elevation Mixed Species forests of East Gippsland for a period of 6 y. The study involved sample seed trap collections and field observations of reproductive components from the following stages of the seedcrop development cycle:

	• Inflorescence bud development
	• Bract fall and flower bud development
	• Flowering and capsule development
	• Natural seed fall and capsule fall.

The timing of reproductive stages during the cycle was very consistent from year to year. Seedcrop development from bud initiation to capsule maturation occurred over a period of about 2.25 y.

Quantities of reproductive components produced and lost were seasonally variable. The number of flower buds produced ranged from 2.4 million to 19.6 million ha⁻¹ over the 6-y period. Mature capsules produced ranged from 0 in 2005 to 7.7 million ha⁻¹ in 2004. Percentage losses of inflorescence buds (generally 20–40%) and flowers (generally 40–60%) were fairly consistent over most years. Generally, abundant inflorescence buds resulted in heavy seedcrops. A heavy seedcrop cycle was followed by a light seedcrop cycle for the period of the study.

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

Records from a weather station near the site suggested that heavy summer rainfall may have been associated with large losses of flowers and maturing capsules in the 2002 season. Neither heavy snowfall nor strong wind events, nor insect and bird predation, appeared to affect the numbers of reproductive components greatly, with the possible exception of wasp attack on inflorescence buds.

We make recommendations to assist in silvicultural planning of harvesting and regeneration of E. viminalis in HEMS forests.

Keywords:

• seeds
• development
• reproduction
• seed crops
• seed years
• seed production
• seed collection
• Eucalyptus viminalis
• East Gippsland