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“Tread Widely – Tread Lightly” – Silvicultural techniques appropriate to different eco-systems
 
“Tread Widely – Tread Lightly”Silvicultural techniques appropriate to different eco-systems

To meet the policy and legislative requirements and good scientific practice, a range of harvesting techniques have been developed based on variation in vegetation communities and associated ecosystems.

Special timbers predominantly occur within blackwood swamp forests, rainforest and mixed forest (wet eucalypt forest with a rainforest understorey).

On the ground, habitats are not discrete units, but more commonly intergrade with each other (Forestry Tasmania, 2009), for instance, mixed forests form a continuum with rainforests related to the time since the last fire (Forestry Tasmania, 2009). For such reasons, selecting an appropriate harvesting technique for a particular site can be complex, and the specific technique selected will depend on the site characteristics and expert advice.

The special timbers forestry management objective is to balance supply to meet current demand and ensure regeneration of the special timber species to meet the needs of future generations whilst conserving the forests where these timbers grow – i.e. conservation through sustainable use.  To achieve this objective, the choice of silvicultural techniques must be both location and species specific, aimed at meeting these management objectives. Whilst single stem selective harvesting may be an appropriate technique for a particular species and particular location, this harvesting method could be detrimental to the successful regeneration of species in other circumstances. This comment is not in any way advocating for the clear-felling of special timbers, it is simply stating that to achieve the best regeneration and forest management outcome, the most scientifically appropriate harvesting and regeneration system that meets the management objectives should be used.

The three silvicultural techniques commonly used in Tasmania when specifically targeting special timbers and identified as being consistent with the definition of partial harvesting[1] are listed below.

[1] Note this list of silvicultural techniques is not comprehensive. New silvicultural techniques can be considered by regulators to meet the definition of partial harvesting.

Over-storey retention

Over-storey retention harvesting is a technique most suited to myrtle-dominated rainforest.

The key prescriptions of over-storey retention harvesting are to:

  • retain an over-storey of 30 healthy, evenly spaced trees per hectares, with at least 50 per cent to be evenly spaced myrtles, and the remainder to include all tree species such as sassafras and leatherwood
  • avoid damage to retained stems to minimise myrtle wilt
  • survey 2 – 5 years after harvest to monitor establishment of regeneration.

Further information on over-storey retention harvesting is provided in Forestry Tasmania (1998) Rainforest Silviculture Technical Bulletin No. 9 Native Forest Silviculture.

Selective sawlog removal

Selective saw removal is the preferred harvesting technique for all special timber harvesting operations in rainforest habitat, other than myrtle-dominated rainforest.

Selective sawlog removal is a harvesting technique where individual trees are selected for harvesting Through this technique scattered individual trees of multiple age classes, whose canopies are not touching, are harvested.

This type of selection system retains the original stand structure and produces small canopy openings especially conducive to the establishment and growth of rainforest tree species.

The key prescriptions are to:

  • retain all non-sawlog trees to provide seed and shelter for regeneration
  • avoid disturbance to areas containing non-sawlog stems
  • avoid canopy gaps greater than 30 m in diameter, retain myrtle seed-trees on a
  • 15 – 20 m spacing
  • survey 2 – 5 years after logging to monitor establishment of regeneration (note where single stem selection was used, post harvest monitoring may not be required).

 

Further information on selective sawlog removal is provided in:

  • Forestry Tasmania (1998) Rainforest Silviculture Technical Bulletin No. 9 Native Forest Silviculture
  • Forestry Tasmania (2010) Silvicultural systems for native eucalypt forests Technical Bulletin No. 5 Native Forest Silviculture.

Group Selection

Group selection is an appropriate technique for wet eucalypt forests rich in special timbers.

The general aim is to harvest approximately 30 per cent of the coupe at each of three stages, such that by the end of the rotation no more than 90 per cent of the coupe has been harvested, with at least 10 per cent of the coupe retained for maintenance of late successional species and structures.

The key prescriptions are that:

  • the emphasis should be on harvesting mature trees
  • >70 per cent of forest canopy should be retained after each harvesting
  • potential crop trees should be retained undamaged
  • harvesting fairways approximately 80 m, or about two tree lengths, wide
  • leatherwood rich patches should be retained undamaged
  • individual sound and safe eucalypts may be retained within the fairways, where practicable and at the harvester’s discretion, at an approximate spacing of two tree lengths to improve aesthetics, seed source, habitat and longer rotation eucalypt sawlog
  • A seedling regeneration survey should be carried out in late summer/early autumn, three years after regeneration treatment.

 

Further information on Group Selection is provided in:

  • Forestry Tasmania (2010) Silvicultural systems for native eucalypt forests Technical Bulletin No. 5 Native Forest Silviculture
  • Forestry Tasmania (2009) Lowland wet eucalypt forests Technical Bulletin No. 8 Native Forest Silviculture.

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