Managing native forest for Blackwood (Acacia melanoxylon) production in north western Tasmania

Summary

Blackwood is a common species in the native forests of north western Tasmania where over 70% of Tasmania's blackwood is cut. It occurs in significant volumes in swamp forests, riverine rainforests and as an understorey component of wet eucalypt forests. The biggest asset for native forest blackwood establishment is the ground-stored seed resource which germinates after disturbances, including logging. Other important silvicultural considerations are form and browsing.

The blackwood swamps were logged selectively until the 1970s when patch clearfelling and burning was introduced, with fencing of the regeneration to prevent browsing. This has subsequently been refined so that swamp forests with a high component of rainforest species are logged selectively to conserve these late successional species, and the use of fire is now minimised. Poisoning with 1080 is used as an alternative to fencing to reduce the level of browsing.

Some riverine rainforest is selectively logged for blackwood although many areas are unavailable due to Forest Practices Code requirements. Retained rainforest trees provide lower branch suppression although myrtle density can be reduced by the myrtle wilt disease. Adequate browsing protection and good form are difficult to achieve in riverine environments.

Selected areas of wet eucalypt forest with a high blackwood density are clearfelled, burnt, sown with eucalypts and fenced to protect the abundant blackwood regeneration resulting from ground-stored seed. Costs of $270 ha⁻¹ were estimated for the fencing. A comparison of eucalypt and blackwood stocking in similar fenced and unfenced coupes up to 11 years old showed the fenced coupes had a mean blackwood density of 2500 stems ha⁻¹ while unfenced coupes averaged 70 stems ha⁻¹. There was no significant difference in the eucalypt stocking between fenced and unfenced areas.

Development of blackwood prescriptions continues, with further work in the blackwood swamps to reduce or eliminate the use of 1080 poison, while the emphasis in wet eucalypt forests is towards cheaper fencing.