Plantation Establishment
Growing trees for agroforestry is a long term investment requiring careful planning and good planting techniques for a successful enterprise. This section on production briefly discusses several topics including in order: planning, site selection, site preparation, planting and management. In relation to management attention is given to fertilising, weed control, pests and diseases. Also a description of pruning and thinning for improved timber production will be included in the management discussion.
This discussion on production should be viewed as starter advise and more research on specific topics may be required. Also different production methodologies may be necessary due to the influences of site conditions, species selected and size of operation.
Planning
When planning the plantation consideration should be given to the following areas. This may require seeking expert advise.
- Assess the potential for your resource: land, capital and time. Also consider alternative land uses in this context.
- Local government regulations for land management, codes of practice and harvesting applicable to your area.
- Tax and insurance matters governing your enterprise.
- Market research - projected value of your plantation and how this may change.
- Be aware of the associated costs of managing the enterprise - major factor in determining size of operation.
Site Selection
Most land can be planted if tree species are selected carefully (Abel, 1997). When choosing a site for a plantation several factors need consideration:
- Conform to current, regional management and tenure policies. Check with local government authority and forestry office.
- Be clear of permanent water ways and power lines.
- Be bordered by adequate fire breaks.
- Have good access for maintenance and harvesting.
- Have appropriate slope i.e. 20degrees to allow planting and harvesting operations.
- Be suitable for the species selected to plant.
- Have soils at least 1 metre deep with a pH between 5.5 and 7.5 (Bailey, 1999).
Site Preperation and Planning
Before planting it is essential that the site be prepared to a high standard. Benefits such as ease of planting, increased tree survival, better weed control and improved growth rates will far out weight the time and effort involved in site preparation. The following discussion identifies the 6 steps to establishing a plantation and contains a brief overview of each step.
Step 1. Clear and Fence Site
- Remove weeds, regrowth and rubbish from site.
- Fence site if required.
Step 2. Mark Out Planting Rows
- Wide enough apart to allow access to maintenance and harvesting equipment.
- On slopes run rows along the contour.
Step 3. Ripping And Cultivation
- Deep rip to 70 cm along each tree row when soil is dry.
- This shatters the subsoil reducing soil compaction and improves moisture infiltration.
- After ripping, cultivate using offset discs or harrows to produce a finer soil tilth.
- This breaks up clods, makes planting easier and reduces air pockets in upper surface layers.
Step 4. Wait For Rain And Pre Plant Weed Control
- Increases soil moisture and helps settle the soil.
- Spray for a continuous 2 metre wide weed and grass free strip along every proposed treeline which is over the ripped line.
Step 5. Planting
- After rain when soil is moist.
- 1000 stems per hectare (4m x 2.5m) is a good stocking density for timber production as it. forces trunk extension, reduces branching and reduces weeds (Bailey, 1999).
- Plant in blocks of between 20 to 50 trees of the same species.
- Rainforest species may perform better if species are mixed.
- Soak seedlings in their pots prior to planting out.
- When planted seedlings must be in shallow depression.
- Water in well.
Step 6. Post Planting Weed Control
- Aim is a weed free zone of 1.5 metre radius until trees reach 4 metre height.
- Use herbicides and/or mulch.
Management
Fertilizer
Requirements are often species specific and the nutrient requirements of the species planted need to be assessed before a fertilizer regime can be developed. This assessment should identify the appropriate fertilizer and application rates.
Usually fertilizers are applied at planting and should not be placed too close to plans as this will cause damage. Doses should be placed at least 30cm from the plant on the downhill side. Follow up application commonly occurs after 9 and 18 months.
Weed Control
It is essential to maintain effective weed control until the trees are established and have grown enough to be away from the influence of weed and grass competition. This is vital to good tree growth and the successful production of a wood crop in a reasonable period.
A weed free zone of 1 to 1.5 metres radius is required around each tree for at least the first year of growth and preferably for the second year or until most trees are over 4 metres. This can be achieved by a variety of methods including the use of herbicides, hand weeding and the heavy application of mulch.
The general area is best maintained by regular slashing. For specific weed problems physical removal or spot herbicide application may be useful.
Pests and Diseases
Insect pests and fungal diseases may develop in the plantation, so periodic inspections are recommended. If damage to the foliage exceeds 40-50%, contact appropriate personnel for advice, e.g. local forestry office. In most situations spraying is avoided and natural populations of predators and parasites are allowed to control out breaks of insects. Matching tree species to your site and maintaining plantation vigor will help reduce the incidence of attack. Find out about the likely susceptibility of a species to insect damage before planting on a large scale.
Pruning
The lower branches of agroforestry trees are pruned to :
- Grow high quality, high value timber.
- Reduce shade and promote pasture growth.
- Improve access and visibility.
- Reduce fire hazard.
- Increase tree stability in windy areas.
Most trees can be pruned to improve timber quality and value (Keller, 1996). Log value is determined by the size and straightness of the tree trunk and the number of knots and branches. Pruning the branches reduces the size and number of knots. Large, straight, knot free logs (clearwood) command the highest prices (Keller, 1996).
There are two basic types of pruning.
- Form pruning - the selective removal of branches to produce a single straight trunk and aids future pruning by controlling tree form.
- Clearwood pruning - the removal of lower branches in such a way as to grow the maximum amount of knot free wood.
When to Prune
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| Clearwood pruning |
Clearwood pruning
Knots are branches that become incorporated into the wood of the tree trunk as it grows. Removal of branches results in knot free timber called clearwood. Clearwood is valuable for veneers, which are obtained by cutting thin layers of timber from logs. Veneers improve the finished appearance and value of lower quality timber products.
Clearwood pruning
Clearwood pruning guidelines
- Start pruning when trees are between 4-6 metres tall.
- Prune lowest branches first, working up the trunk.
- Always leave 3-4 metres of crown at the top of tree.
- Form prune above the clearwood pruned trunk to ensure a single straight stem.
- Prune only to the desired saleable log length.
- Prune each tree according to its height and diameter.
- If possible undertake thinning in conjunction with pruning.
- Remove branches close to the collar but don't cut the collar, as this will impede healing.
- Small branches should be removed with pruning shears or secateurs (Diagram 1).
- Large branches will require a pruning saw and several cuts to avoid tears (Diagram 2).
| Diagram 1. Pruning small branches | Diagram 2. Pruning small branches |
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Source: Baily, 1999
Thinning and Tree Selection
There are two reasons why more trees are planted than are required.
- Allows for the selection and management of the best trees for final crop trees.
- Forces the plantation to grow tall and straight with less vigorous lower branching (Reid and Wilson, 1986).
Thinning is done to maximise the growth of the final crop trees and minimise the number of trees to be pruned.
When to Thin
First thinning should be done at first clearwood pruning. Early thinning is biased towards malformed and smaller trees to ensure the right planting density is maintained and to allow resource use to be concentrated on the better trees. As trees grow older they require more space to grow. The amount and timing of thinning older trees depends on growth rates and initial spacing. Crowding of the tree crowns gives a rough indication of when thinning is necessary. Once tree crowns close in and almost touch, the plot needs thinning.
Selecting Trees
Reid and Wilson, 1986 have developed two criteria for the selection of trees to be removed and those to be retained and pruned.
- Trees that are to be thinned out immediately
- Do not have straight trunks.
- Lean more than 5 degrees.
- Have missing, broken or dead tops.
- Have multiple stems or very large branches.
- The trees that are the best to prune are those that
- are vigorous i.e. tall, healthy with large trunks
- are the straightest
- are well spaced i.e. have enough space to grow freely
This process of selection and thinning should be carried out at each pruning visit or until the final number of crop trees is reached.