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Forestry Fact Sheet Number 6

 

Introduction

The aim of this fact sheet is to provide information to assist in the decision-making and effective management of second rotation Eucalyptus globulus (Tasmanian blue gum) plantations. The topics covered include re-establishment methods, slash management, and coppice control/ management.

 

It is important that growers decide prior to harvesting how they want to manage their site in the second rotation, as this will determine what operations need to occur, possibly within 24 hours of the trees being harvested.

 

The two options for management of land after clearfelling Tasmanian blue gums are replanting or regeneration from coppice. The option selected will depend on the owner’s objectives, yield of the previous plantation, stump survival and economics.

 

Replant or Coppice?

Tasmanian blue gum produces coppice shoots reliably and vigorously. Coppice regeneration is used widely overseas and potentially provides better early growth, reduced costs and reduced time between harvests. The main advantage of coppice is the substantial pre-existing root system that sustains rapid early growth.

 

Most of the costs associated with plantation establishment using seedlings will not be incurred when managing plantations under a coppice regime. However, regeneration by coppice is not as simple as watching it grow. Regrowth may be quite variable and it requires thinning. The stability of the remaining stems is also a concern, but has not been a significant issue to date.

 

If a site is to be re-established with seedlings, it must be prepared well and planted during the appropriate planting season (June – August in the Green Triangle). A plantation harvested in August would therefore lie unproductive for at least ten months prior to replanting. However, replanting has the advantage of capitalising on genetically advanced planting stock and improved establishment and management techniques.

Replanting

Stump Survival

After harvesting there will be a delay before the coppice begins to shoot. This can range from weeks to several months depending on the time of harvest and seasonal conditions. There can be a large variation in coppice development, even within the same plantation. A good rule of thumb is to wait until most of the stumps have coppice shoots at least 30 cm tall. This will ensure that most late development of the coppice can be seen. For a pulpwood rotation, if stump survival is less than about 600 stumps/ha, there may be insufficient to produce a fully stocked coppice stand and replanting should be considered. Stump survival in Green Triangle coppice plots has been between 80 and 90%, or 800 - 1000 stumps/ha.

Methods of Coppice Suppression

Coppice will need to be controlled if the site is to be replanted. The main methods for controlling coppice are:

1. Application of herbicide to cut stumps
2. Application of herbicide to coppice foliage
3. Excluding light from stumps
4. Manual shoot control
5. Grazing

Application of Herbicide to Cut Stumps

Applying herbicide to freshly cut stumps can be the most effective way of controlling coppice. To curtail shoot production and kill stumps, herbicide should ideally be applied to the stump within 24 hours after felling. Herbicide can be applied using spray equipment or a brush. An emerging technology is herbicide spray nozzles fitted to the felling head of harvesting machinery.

 

Initial trials with Glyphosate and cut stump applications indicate that a concentration of 50% Glyphosate/50% water at up to 24 hours, and 100% Glyphosate (360) at up to 48 hours after harvesting gave effective coppice control. Lower concentrations were not fully effective, even if applied within half an hour of felling.

 

The direct application of Glyphosate to treat cut stumps in a thinning operation is discouraged, because, with these rates of Glyphosate, there is a risk of ‘flashback’ (when the chemical is taken up, and kills remaining live trees through root translocation).

Application of Herbicide to Coppice Foliage

To control regenerating coppice allow the coppice to grow until it is around 1m in height. Spray the foliage with herbicide when it is actively growing. If the coppice is taller than 1 metre trim the foliage to below 1 metre and then apply the herbicide. Results indicate that spraying at the maximum rate of Glyphosate is the best option to kill coppice in a single operation. It is essential to use a misting spray to cover every surface of the coppice.

 

It is critical to have complete foliage coverage and penetration. This is achieved with minimum water rates of 300L/ha. Spray applications need to be a double overlap with the coppice sprayed from opposite directions. Trial evidence indicates that there is little to no translocation of herbicide between coppice stems via the stump, so if an individual stem is not sprayed, it will not die.

Excluding Light from stumps

Covering stumps with a layer of soil when ripping and mounding a site for replanting has been tested as a method of suppressing coppice regeneration. It is not a reliable method to control coppice. Harvesting slash is also unreliable, because it is rarely thick enough to suppress or inhibit coppice. An associated problem with this method is that if coppice re-appears amongst the replanted seedlings, control options are limited to manual control.

Manual Shoot Control

Overseas, where labour costs are lower, ‘manual bashing’ is sometimes used to control coppice. Coppice is repetitively cut from the stump using machetes or similar. This is very labour intensive and would generally be required over several years.

Grazing

Heavily grazing with cattle, sheep or goats in a plantation area after felling, or once coppice regeneration has started should suppress coppice growth. Shoots are repetitively browsed or pushed over and in time the ability of the stumps to produce shoots decreases, which will eventually result in their death. This method is unreliable, inconsistent and may take several years to be effective. Eucalypt coppice is not particularly good fodder and maintenance of stock condition needs to be considered.

What replanting involves

Second rotation plantation establishment using seedlings needs to be carefully planned, as coppice must be fully controlled before seedlings can be planted. If the decision is made to replant, a variety of benefits can be gained including the availability of better genetic material, latest establishment techniques, reduction of fire hazard (if the slash is removed or burnt) and consistent stocking throughout the plantation. In order to replant, both the slash left after harvest and the coppice shoots will have to be managed.

 

In some Tasmanian blue gum clearfelling operations trees are cut, delimbed and debarked at the stump. This leaves a very high level of slash spread across rows. In clearfelling operations where delimbing and debarking are done at the edge of the plantation and adjacent to the chipping operation, slash conditions and the issues faced in re-establishment are completely different. In this case it will be important for long term site productivity that the slash be brought back onto the site, and distributed across the site to suit re-establishment operations. Some options for slash management include:

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 with in the rows, and 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 spread of the slash, as typically ‘islands’ of heavy slash will be separated by bare ground.

 

Mechanical Slash Treatments

Breaking down slash mechanically allows the preservation of organic matter and nutrients 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 burying the slash. Subsequent cultivation operations may be more difficult however; as the same volume of slash still exists as prior to chopper rolling just that it is in smaller pieces. Early chopper rolling trials have shown that Tasmanian blue gum slash is too springy to chopper roll well 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 one 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 to suggest that 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 tool.

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 left on site and produced in coppice thinning, 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.

 

For further information contact PIRSA Forestry

 

 

Disclaimer: While this publication may be of assistance to you, the government of South Australia and its officers do not guarantee that it is without flaw of any kind or is wholly appropriate for your particular purpose. The Government therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any information in this publication.

 

 

Last Revised February 2008