Seedcrop development in Eucalyptus denticulata and E. fastigata in HEMS forests of East Gippsland.  M. D. Murray, M. T. Lutz and P. C. Fagg.  March 2004.  29pp. (unpubl.)

SUMMARY

Case studies assessing the seedcrop development processes in mature age Eucalyptus denticulata (Errinundra shining gum) and E. fastigata (cut-tail) were conducted over a period of five years from 1975 to 1980 on the Errinundra Plateau in East Gippsland, Victoria. Collections of fallen material were used to determine the sequence and timing of development of each component of the seedcrop development cycle for each species.

Seedcrop development in E. denticulata occurred over a period of approximately 2-2.5 years from initiation of inflorescence buds to capsule maturity. For E. fastigata, the seedcrop development cycle proceeded over a 2.5-3 year period. The development and appearance of components of the seedcrop cycles of both E. denticulata and E. fastigata were very regular in respect to timing. For example, flowering consistently occurred in the February-March period. Production and loss of components due to natural abortion and/or disease or attack by animals (usually parrots) varied greatly between years.

Free seedfall was recorded in all years of the study even following years of light flowering or heavy loss prior to capsule maturation. For example, collections suggest that 100% of the 1977 E. denticulata flowering crop was aborted, however about 2 million free seeds per hectare were recorded as fallen from October 1977 to September 1978. Seedfall in E. denticulata was greatest during late summer/early autumn. The peak numbers of free seed per hectare per day ranged from about 5,000 in 1976 to about 26,000 in 1975. Patterns of seedfall were less pronounced in E. fastigata with slightly higher falls recorded from March to May. Mean daily rates of fall of free seed ranged from zero to almost 9,000 during the study period.

Significant quantities of seed fell in capsules, especially in E. denticulata, where an average of 29% of total seed produced fell in capsules. This seed is essentially unavailable for regeneration in a forest.

The study showed that monitoring of bract fall (in summer) will give indications of the extent of the potential flowering and future seed set, although this predictive value was better for E. fastigata than E. denticulata.

There were no discernible patterns in seedcrop production or loss over time. That is to say that years of high production and or low to moderate loss of components did not appear to occur on a regular cyclic basis such as the biennial bearing pattern seen in other eucalypt species and some fruit trees. Such a cycle may occur on a longer time scale, perhaps only once every 7-10 years, than that covered by this study.

Identification of the magnitude of the seedcrop development stages for these species enables the forecasting of crop potential for the collection of seed and use of seed tree systems in HEMS harvesting operations in East Gippsland. However, the variability in the proportion of the potential seedcrop that may be lost must be taken into account when predicting seed availability. Also, the timing and maturation of development stages may vary across the range of occurrence of the species.

The methodology of monitoring seedcrop development and prediction of potential seedcrops using under-canopy seed traps is assessed and alternative methodologies discussed. The requirements for additional research into the relationships between seedcrop development and climate, topography (aspect and shelter) and location including latitude and longitude and elevation are also considered.