The use of shelterwood in Eucalyptus regnans forest: the effect of overwood removal at three years on regeneration stocking and health

Abstract

Summary Shelterwood regeneration was tested as an alternative to clearfelling of Eucalyptus regnans dominated forests in southeast Victoria, using two retention levels, 30% and 50% by basal area. Removal of the retained trees was carried out 3 years after the regeneration felling. Stocking of regeneration following overwood removal was generally unsatisfactory, particularly in terms of its distribution. Large contiguous unstocked areas (0.35 to 0.7ha) were evident in all treatment units. The sources of seedling damage included tree felling, log preparation and extraction related activities such as snig track construction, log winching and snigging. Where there was soil profile disturbance, usually related to snig track construction, the vegetation was generally destroyed, accounting for much of the reduction in seedling density and stocking. In the remaining area substantial seedling damage was attributed to tree felling. Therefore, while a similar snig track network is necessary regardless of the level of overwood retention, the level of damage caused by felling trees, log preparation and winching can be expected to be directly proportional to the number of trees felled. Lower shelterwood retention levels should result in reduced damage to established regeneration. There was no conclusive evidence that dominant or co-dominant seedlings sustained more damage than intermediate or suppressed trees, although there were proportionally fewer dominant seedlings in 3 out of 4 replicates following the operation. The effect of shape, size and topography of the treatment units influenced the extent of the damage. A high perimeter to area ratio and relatively small felling plot size meant that options for directional felling of the trees to minimise regeneration damage were frequently constrained by the proximity of the boundary, and concentrated felling damage resulted in large unstocked areas. If damage to regeneration is to be reduced to an acceptable level during overwood removal operations at three years after the regeneration felling, careful consideration should be given to coupe layout and felling prescriptions, the slope of the coupe, particularly near coupe boundaries, and the machinery used for extraction.