Regeneration from seed trees in high elevation mixed species forest in East Gippsland.  M. T. Lutze, J. D. Dellbridge, D. Terrell and L. Warren.  September 1999.  45pp. (unpubl.)

SUMMARY

A study was undertaken in the period 1995-98 to:

• determine the likely success using the seed tree system as the sole seed source in regeneration of the high elevation mixed species (HEMS) forest of eastern Victoria;
• examine the processes by which successful regeneration using the seed tree system occurs;
• identify factors which determine success or failure of the seed tree system.

Twelve (6 in 1995 and 6 in 1996) coupes were selected as case studies from across the geographic and elevation range of HEMS forest. At each coupe ten retained trees were selected for study and, following autumn slash-burning, funnel seed traps and paired germination plots established on burnt and disturbed seedbeds in close proximity to the selected trees. Germination plots and seed traps were monitored regularly and seedfall, germination, mortality, survival and height growth of eucalypts were measured up until winter 1996 or 1997. In 1997 a further three coupes were set up with semi-operational examples of seed tree and clearfall systems. Two coupes were slash-burnt in autumn, the other rough-heaped (then burnt in autumn) and retained trees poisoned in winter to induce seedfall. Seedfall was monitored long enough to measure the peak and decline after induced seedfall. Regeneration was monitored by a system of 4 milacre plots on a 40 x 20 m grid in early winter, early summer and the following early winter.

It was found that:

• Seedfall was induced by slash-burning and poisoning and, as a result, peak seedfall occurred within one month of burning and 2 to 3 months of poisoning. Protracted seedfall may occur after the induced peak and winter/spring seedfall may exceed recommended artificial sowing rates on some coupes.
• When rainfall was not limiting there was a trend towards increasing total germination percent with increasing autumn germination, which is consistent with fewer pre-germination losses of seed with increasing speed of germination. Peak germination in spring after autumn seedfall was common at higher elevations or on cold sites at lower elevations, which may be an important process to avoid risk of regeneration failure. Thus the perceived risk of failure of regeneration as a result of autumn germination followed by heavy winter mortality did not eventuate because germination peaked in spring on such sites.
• Germination and survival were not consistently different between burnt and disturbed soil seedbeds in the year of high rainfall, but were greater on disturbed rather than on burnt seedbeds in the year of low rainfall.
• Estimates of mean germination and seedling percents to late autumn, approximately 15 months after slash-burning on burnt and disturbed seedbeds had very wide 95% confidence intervals which may have been the result of poor estimation of seed supply or the variation in the quality of seedbeds.
• Seedling percents were acceptable on most coupes in the year of high rainfall, but they were unacceptable in the year of low spring rainfall. However the very high seedfall from seed trees resulted in acceptable seedling density in the 1997 coupes. Seedling density was greater on the seed tree than on the clearfall parts of the 1997 coupes, because seed supply was greater.

Artificial sowing in winter should remain in place, until several factors such as the assessment of, and variation in, seed crops and the financial implications of seed tree retention, are investigated. However, the following changes to operational practices are indicated by this three year study:

• Select and retain seed trees in all HEMS coupes with adequate seed crops, not just in routine coupes or coupes which can be slash-burnt.
• Where seed trees are used, ensure that seedfall occurs via slash-burning of adequate intensity or via poisoning in autumn if a disturbed soil seedbed is used.