Seedcrop development in Eucalyptus obliqua and E. cypellocarpa in HEMS forests of East Gippsland.  M. D. Murray and M. T. Lutze.  February 2004.  26 pp. (unpubl.)

SUMMARY

The seedcrop development cycles of Eucalyptus obliqua and E. cypellocarpa were examined over a four year period from 1994 to 1998 in High Elevation Mixed Species forests of East Gippsland, Victoria. Only one site for each species was evaluated.

Collection of material using seed traps allowed for the identification and monitoring of the recognised stages of the seedcrop development cycle, as follows:

• inflorescence bud initiation and development;
• bract production, umbellate bud emergence and development;
• flowering; capsule and seed maturation;
• seed fall;
• capsule fall.

The timing of reproductive stages during the cycles of both species was very precise. The quantities produced per hectare, however, were highly variable between years. Subsequent losses of components were also extremely variable. The average loss of flowers and immature capsules ranged from 39% to 100% for E. obliqua and from 46% to 99% in E. cypellocarpa.

Peak flowering was consistent between years, occurring in February/March for E. obliqua and November/December for E. cypellocarpa.

Seedfall was recorded all year round for both species with only one collection failing to yield any seed from the E. obliqua stand. Peaks of seedfall were recorded in E. obliqua in spring and autumn of each year while E. cypellocarpa did not have any defined regular peaks. The magnitude of seedfall was variable, with the mean number of viable seeds per hectare per day ranging from a low of 0 to a high of 14,130 for E. obliqua and from 440 to 15,190 for E. cypellocarpa. It was not determined if the levels of available seed were sufficient for effective regeneration of the forests studied in the event of a wildfire or for the selection of individual seed trees or seed collection during harvesting operations.

There were no causal relationships established between measured climatic events and seedcrop production of either E. obliqua or E. cypellocarpa. However, both species produced a reasonably good seed crop in the same year, indicating the climate does influence seedcrop production. Climate (temperature and rainfall) was measured at a central Automatic Weather Station rather than at the individual study sites. Microclimate events (frosts, localised strong winds, relative humidity or rainfall) that were not measured may have affected the seedcrop production of the two species.

Recommendations are made for the monitoring of seedcrop components as part of operational planning for forest utilisation to allow for harvesting to be better aligned with the availability of maximum seed supply for regeneration. Future research including improved methods to further enhance the understanding of periodicity of seedcrop production and seed availability of these two species are also recommended.