Review of silvicultural systems for harvesting Eucalyptus delegatensis forests on dolerite plateaux in Tasmania

Summary

Past selective loggings in high altitude multi-aged Eucalyptus delegatensis forests inefficiently utilised the timber resource. However, the small forest clearings created by selective logging are stocked by healthy regrowth that established following wildfire. Pulpwood markets now enable more efficient logging through integrated pulpwood-sawlog operations. The regeneration on some sites following clearfelling has been severely damaged by frost. Canopy cover provides a barrier to nocturnal radiation loss, thus preventing severe frosts. Therefore shelterwoods are currently being explored as an alternative to canopy removal by clearfelling. Shelterwoods and selective logging systems are essentially similar in terms of forest regeneration practices but differ according to the resultant age structure of the regrowth forest. With the former system, once the even- aged regrowth is considered relatively immune from frost damage the overwood is cut. The decision to use either selective or shelterwood systems will require further research to explore spatial pattern, density, basal area and form of the retained trees in meeting the conflicting objectives of both providing canopy shelter from radiation frosts for eucalypt regeneration and also freeing the saplings from intraspecific competition with the overwood. If, in addition, trees are retained for their growth potential as is the case in selective systems, then the competitive influence of surrounding trees must also be considered. Mathematical modelling is a possible approach to this complex silvicultural problem.