Before seedlings can be planted, the land must be cleared. Land clearing involves:
• Removal of vegetation that may compete with the
growth of young trees.
• Access of machinery.
• Removal of debris.
• In some cases, cultivation of the land.
Land Clearing Techniques
Various methods are used to clear land:
• Herbicide spraying
• Mechanical operations
• Burning.
In most cases a combination of techniques is used to obtain the best conditions.
Herbicide Spraying
Herbicides are used to provide vegetation-free land ready for planting or mechanical clearing. Key factors to be considered for herbicide spraying are:
• Planning – to ensure the right chemicals are used with the
appropriate equipment in a safe manner.
• Target species – ensuring the correct choice of chemical is
used for a particular species of vegetation. The correct rate
of application must also be considered.
• Topography – this will determine the type of application (hand,
ground based or aerial, depending upon the land’s steepness).
• Climate – spraying is only conducted during calm conditions,
as overspray caused by wind drift may affect nearby plantation
crops or adjoining vegetation.
• Proximity – to dwellings and crops. Allowance is made for the
proximity of water ways, streams and stream life, and of
non-targeted species.
Mechanical Clearing:
A range of mechanical operations are employed to prepare and clear land of vegetation and debris. Key factors to be considered for mechanical clearing are:
Topography – consideration is made for the lie of the land. Various mechanical applications are best suited for particular site conditions.
Vegetation – the size and species of vegetation will influence the most practical mechanical means to employ.
Availability of trained personnel – this is extremely important as the competence and attitudes of all involved will lead to a successful operation and safe practices.
Climate – wet clay soils may risk compaction by heavy machinery, therefore making planting difficult and affecting seedling root growth.
Impact of soil erosion, soil type and water quality – intensive soil disturbance during a clearing operation may cause a reduction in site productivity. This may be caused by the erosion of soil from the site. Eroded material may discharge into, or block nearby waterways. The loss of vegetation will increase water run-off which will continue until the forest cover re-establishes. This can be reduced through installing cutoffs to cleared tracks.
Ground cover – undisturbed strips of ground cover can be left (to trap eroded soil sediment) beside waterways and wetlands to filter run-off material.
The choice of mechanical land preparation – it is extremely important to ensure the best mechanical application is chosen for site. An incorrect choice could have a serious impact in many of the situations set out above, and prove costly for the forest owner.
The type of operations used in land clearing are:
• Hand clearing
• Discing
• Root raking/Line raking
• Line dozing
• Gravity rolling
• Tractor crushing
• Towed rolling
• Ripping
• V-Blading
• Tracking and sidecasting to obtain access.
Most of these operations involve crawler tractor units of varying capacities and capability, fitted with a cultivator. Well planned land preparation will:
• Clear land of scrub or vegetation of varying size and density;
• Reduce sediment erosion and soil runoff;
• Provide access for planting;
• Prepare the ground for planting.
Burning Operations:
Large scale burning operations are now rarely used to clear land for forestry in New Zealand. Herbicides and mechanical methods are preferred. Burning must be managed and carefully planned by trained and experienced people, as many risks are involved.
Burning is, however, the quickest and cheapest way to remove branches and other debris left after harvesting or initial clearing of large areas. A combination of mechanical operations and herbicides is commonly used to reduce vegetation to a state where it will burn.
Burning operations are sometimes used on steep landscapes where machinery cannot get access, to remove logging debris and other vegetation. Careful planning is essential to avoid the possibility of an adjoining forest or plantation catching fire. This is why fire breaks are needed.
A fire break is formed by using machinery to remove vegetation, producing a clear strip that completely surrounds the burning site. It is designed to contain the fire within a restricted area.
A burning operation (‘burnoff’) can be started deliberately by:
• Manual ignition – an operator equipped with a flame thrower
can be used to start the burn. Safety is the main concern.
Most burnoffs are supported by crawler tractors, water tanks
and fire control crews.
• Helicopter ignition – a helicopter can also be used to start
the burn by dropping burning flammable jelly or firelighters.
This quickly starts many small fires in a line. This means the
burn can be managed and manoeuvred evenly. Risk to the
operator is reduced but safety is still extremely important.
Key factors to be considered in a burning operation are:
Topography: Operators need to know the type of terrain they are working on. Such factors as:
- land features
- steepness
- light to heavy vegetation
- location of water ways, catchments
- location and type of adjacent vegetation
- proximity of dwellings and roads.
Weather: Weather conditions are extremely important. Less fierce burns are obviously more desirable. Factors to be considered are:
- Wind direction away from dwellings and adjoining stands;
- Burns during early winter when fire hazard is reduced;
- Burns in late afternoon to early evening when temperatures are
down.
Ground cover: It is important to know the quantity of material being burnt as this controls factors such as burn time, intensity of fire and control requirements. Other factors such as the moisture content present in the ground cover must be known for the same reasons.
Fire breaks: Careful thought must be given to fire breaks – are they big enough and in the right places? Also, creating fire breaks may increase sedimentation and runoff that may enter waterways. The type of soil will determine the type of measures taken to prevent soil erosion. Cut-offs on hill country are commonly used to control sedimentation runoff.
Trained personnel: As with any successful operation, trained, experienced personnel are extremely important. Consideration must be made for:
• The safety of operators throughout the operation;
• The use of protective clothing and equipment;
• Adequate resources to control the fire;
• Well-marked escape routes;
• Well-established communication procedures.