Tasmanian Blue Gum Plantations -Second Rotation/Site Clearing

Windrow & Burning:

Site clearing using burning is very effective, however in the long term, soil nutrient depletion may prevent this method from being adopted over several rotations.

Using a small D5 equivalent Bulldozer equipped with a rake it is possible to drive between the rows, pushing the slash into a windrow at right angles to the rows. Burning should be conducted in April/May after fire restrictions have been lifted. This method cleans the site particularly well between the rows and damages the new coppice shoots. This method is particularly suited where ripping and mounding between the rows is required. It is somewhat less effective if mounding over the stumps, as some slash is left within the rows, which is then incorporated into the mound.

Broadcast burns can also be used to reduce slash levels, however the effectiveness of the burn will depend on the dryness and spread of the slash, as typically ‘islands’ of heavy slash will be separated by bare ground.

Mechanical Slash Treatments:

Breaking down slash mechanically maintains organic matter and nutrients on the site, however its effectiveness in terms of slash management needs more investigation. Some of the mechanical slash options include:

Chopper Rolling:

Chopper rolling is one of the most effective mechanical slash treatments available where two heavy, bladed, offset rollers break down and bury the slash. Subsequent cultivation operations may be more difficult however; as the same volume of slash still exists as prior to chopper rolling, just in smaller pieces. Early trials have shown that Tasmanian blue gum slash can be too springy to successfully chopper roll in the year after harvesting and leaving the slash longer to dry out may produce better results.

Cultivation:

Ploughing of any type is likely to be ineffective unless the site has been chopper rolled or windrowed and burnt. After chopper rolling a Bräcke spot cultivator can be used to cultivate planting sites directly through the slash and will cultivate a spot in most conditions except where there is a very high slash level. This is the most cost effective method to re-establish a site; however the level of cultivation is minimal and may not be sufficient for good growth.

Scalping:

Scalping the planting lines using a small dozer with snowplough blade has been tested and proven to be unsuccessful due to the build-up of slash between rows, which precludes any further machinery access.

MANAGING REGENERATION FROM COPPICE

Thinning:

Each stump will typically generate one to six large stable shoots. A stocking of 900-1000 stems/ha should be targeted for pulpwood production purposes in the Green Triangle. To achieve this stocking the majority of stumps will be thinned to a single stem with the retention of two stems adjacent to gaps and dead stumps. Replanting seedlings to make up the stocking deficit is not an option, as they cannot compete with rapid initial coppice growth.

Shoot stability needs be considered when managing coppice, as wind can potentially cause heavy losses of coppice shoots during the first two years. There is evidence that suggests clean-cut stumps produce stable coppice, because on damaged stumps torn or frayed bark strips easily from the stump destabilising the coppice. Low cut stumps also tend to have more stable coppice shoots. Experience in WA and overseas suggests that shoots on the windward side of the stump are more stable than those on the leeward side.

To guard against wind damage coppice can be thinned in two stages. Select two stems per stump at approximately age two, then select only one stem to remain the following year. Most growers take the risk and thin to one stem per stump at age two to save on costs and to date no significant losses have occurred. It is estimated that thinning can be done for under $700/ha. This operation can be done with a chainsaw, brush cutter, pruning shears or axe, but brush cutters with a chainsaw bar are the preferred tools.

Weed Control:

Weed control trials have yet to be carried out in coppice areas; however there will be limited need for weed control. Furthermore, weed control is difficult due to poor access when slash is left on the site and is likely to be best done aerially.

Fire Risk:

Due to the high level of slash produced in coppice thinning and left on site, the fire risk in coppice is much greater than in first rotation and replanted plantations. Firebreaks must be well maintained and plantation owners should consider insurance at an earlier stage.