Regeneration after 8 years in artificial canopy gaps in Mountain Ash (Eucalyptus regnans F. Muell.) forest in south-eastern Australia

We report on a study of regeneration of Mountain Ash (Eucalyptus regnans) forest in S.E. Australia in artificially created canopy gaps (0.01–2 ha) and clearfelled coupes (4–27 ha) with different seedbed treatments. Treatments were applied in 1988, 1989, and 1990. Our results are based on measurements 8 years after harvesting.Gap size had a significant influence on sapling height and diameter growth. The effect was substantial for the canopy openings larger than 2 ha, but inconsistent across the smaller gap sizes. Mean height of the largest diameter saplings was significantly greater in the clearfells (13.2 m) than in the 2 ha gaps (10.7 m), while mean heights in the smaller gaps ranged from 6 to 8.8 m. Mean sapling diameters (at 1.3 m) in clearfells and 2 ha gaps were 9.6 and 7.9 cm respectively compared with 3.8–5.8 cm for the smaller gaps.There was lower stocking in all treatments for the third regeneration year (1990), when regeneration operations were delayed by high summer and autumn rainfall. Stocking ranged from 12 to 33% for the smallest gaps, increasing with increasing gap size to 34–64% for 2 ha gaps and 48–76% for clearfells. Results were consistent with a previous study 3 years after treatment, indicating that stocking at 8 years is still dominated by initial stand establishment rather than by stand development processes.There was no significant influence of seedbed preparation on any of the variables tested at year 8; this was in contrast with earlier findings at year 3 when seedling height was significantly higher on burnt sites compared with mechanically disturbed sites. The growth of non-eucalypt competitors was also influenced by gap size and year of regeneration treatment. The main competitor species differed between larger and smaller clearings and between sites.Results indicate that using a silvicultural system based on smaller gaps (<2 ha) in this forest type is likely to result in reduced timber production potential compared with clearfelling.