Effect of time of sowing and seedbed type on Eucalyptus regnans germination and establishment on high elevation sites.  P. Dignan.  March 2002.  25pp. (unpubl.)

SUMMARY

This report describes a series of trials looking at the effect of time of sowing on germination, survival and establishment of mountain ash (Eucalyptus regnans) on high elevation sites (>800 m). Following clear-felling, mountain ash regeneration operations are usually concentrated in mid to late Autumn, when conditions are suitable for slash burning. Seed applied at this time may start to germinate almost immediately and Autumn germination is generally considered advantageous. However, high Winter mortality of Autumn germinants is common on high elevation sites, and can lead to regeneration failure in some cases. Later sowing may ensure that a higher proportion of the applied seed does not germinate until Spring, thereby reducing the risk of Winter losses.

Trials were carried out at four sites between 1995 and 2000. The first site was established in 1995 on a disturbed soil seedbed, with one site established in 1997 and two in 1998 on burnt seedbeds. Interactions between sowing time, seed provenance and seedbed preparation were also considered. Seed from both high and low elevation provenances were used in each of the trials and two seedbed preparation variations were used; seedbed preparation in Autumn was carried out for all plots and half of the plots were also lightly raked immediately prior to sowing.

Three sowing times were used in 1995 (Autumn, late-Winter, Spring) and four in 1997 and 1998 (Autumn, mid-Winter, late-Winter, Spring). This report describes the outcome of these trials in terms of progressive germination patterns, total germination, the number of and competitive position of live seedlings 18 to 30 months after the establishment of the trials and the potential stocking outcome for each site. A similar experimental design was used for all four sites and, while analysed separately, the results are presented and discussed together.

• In each of the studies reported, time of sowing had a major effect on the pattern of germination, total germination and seedling establishment. However there were differences in the effect of sowing time between sites and between experiments carried out in different years.
• Of the Autumn sowings, only the earliest (27 March) had significant Autumn or early Winter germination, much of which did not survive. The principal period of germination for the Autumn sown seed was mid August to late September. Germination of the Winter sowings were generally comparable to the Autumn sowings. Much of the germination of the mid Winter sowings occurred from mid September to mid October, shortly after the peak germination period for the Autumn sown seed. The initial germination of the Spring sowing was almost invariably the poorest by comparison with the earlier sowings, although there was generally a second flush of germination in the following Autumn.
• There was evidence that seedbed characteristics have a major influence on germination. The freshly prepared seedbeds generally had better germination, markedly so in some cases. The differences observed are almost certainly due to the failure of the seed to penetrate the soil surface on seedbeds which have been prepared for some time before sowing, with consequences for seed moisture and temperature flux.
• There were some differences noted between seed from different provenances but there was not a clear distinction between the performance of seed from high and low elevation collection sites.

The overall outcomes from the germination monitoring indicate that, on seedbeds prepared by slash burning in Autumn, sowing between Autumn and mid-Winter results in significantly greater germination than late-Winter or early-Spring sowing. The germination response was generally enhanced by additional seedbed preparation immediately prior to sowing, particularly where there was an appreciable time lag between initial seedbed preparation and seeding. Spring sowing is clearly not a reliable regeneration option, probably because of insufficient time for adequate germination before increasing soil temperatures induce dormancy or soil moisture dynamics become unsuitable for germination.

The results for the site where seedbed was prepared by soil disturbance provide indications that seed germination dynamics may differ between burnt and disturbed seedbeds. Germination from the Autumn sowing was substantially lower than that from late Winter (31August) sowing. Although based on only one trial, Winter sowing may be preferred on high elevation sites prepared by mechanical disturbance in late Autumn.

Seedling establishment results and the potential stocking of each site tends to reflect the results of the germination monitoring. The number of established seedlings at the end of the monitoring period at each site suggests that satisfactory stocking can generally be achieved by Autumn or mid-Winter sowing at the standard sowing rate of 200,000 viable seeds per hectare. Lower sowing rates resulted in unsatisfactory potential stocking on some sites, particularly for the later sowings and on older seedbeds. The development of supplementary seedbed treatment, such as harrowing or raking of the seedbed surface, may be of value where delays between site preparation and sowing occur or in cases of seed scarcity or high seed cost.