Teak/Coffee Agroforestry Systems

Background

Even in Solomon Islands, which has near perfect conditions for growing teak, the trees take 20 years to reach a commercially harvestable age. While pressure for land is generally not a major problem, there is considerable pressure on coastal land with easy access to the water. One of the major problems facing growers is the distance they have to move logs or timber to get access to the water for transport. Traditionally coconut plantations occupy the waterside sites. While of low value, copra is still one of the major sources of cash for many rural communities. One potential answer to this is to make the remaining land with reasonable water access, multi-purpose and we have been examining ways to integrate teak with other cash and food crops in an integrated agroforestry approach to growing high value timber.

Whole of life approach to tree growing

Tree crops such as teak and mahogany in Solomon Islands. have been regarded as a single use for the land, though some growers have tried cocoa beneath the trees. The project advocates a different approach based on mixed species planting of trees and intercropping the trees with food and cash crops. There are clearly defined steps in this approach which are detailed below:

Step 1 Mixed species planting

Getting growers to thin trees is a huge problem as each teak tree is seen as having a very high potential value and owners are reluctant to remove a tree they see as being worth thousands of dollars. As a result, most plantations are overstocked with trees that cannot grow due to competition for resources and less than 20% of the trees have any real commercial value . To make matters worse research by this, and other ACIAR teak projects has shown that once teak has been suppressed by competition, it will not respond to late age thinning and the thin, suppressed trees will remain suppressed even when the competition is removed.

To overcome this, the project team developed a system of planting teak with alternating rows of a local tree, Flueggea flexuosa. Flueggea is a multi-purpose tree that is used for fencing, housing, furniture and firewood. At the start of the plantation it grows with the teak, forcing the teak to grow straight with few branches as both species compete for the available sunlight. When the canopies of both species begin to touch, around 4 years after planting, the flueggea is gradually removed and the community has a source of valued timber. This can take place gradually over the next few years. After about 6 years the flueggea will have done its work and the remaining teak will have good form and clear stems. Grown in this way, teak is virtually self-pruning with very few branches on the lower stem.

Step 2 Inter-cropping with food crops

This takes place soon after the plantation has been established. As there is adequate sunlight, virtually any of the traditional food crops can be grown.

As the trees develop, the amount of shade increases and the range of crops that can be grown will shift towards the more shade tolerant species. If the rows of trees are oriented to make best use of the track of the sun, this helps prolong the light levels within the plantation.

The project publishes a list of crops that tolerate different levels of light. This and more detailed descriptions of the mixed species system, can be found in the Agroforestry Booklet which is available for download from the Resources section of this website.

Step 3: Coffee and Teak

The final step in the integrated system occurs once the alternating rows of flueggea have been removed. There will now be an 8 metre gap between rows that has dappled shade from the teak. These are ideal conditions for growing coffee.

The project has trials underway on Kolombangara Island in Western Province looking at different species of coffee, spacing of the plants and levels of available photosynthetic radiation beneath the teak trees. As most teak is grown in the lower altitudes, Arabica coffee is not suitable. While Arabica is considered the premium coffee and commands the highest prices, there are many other species that will grow over a wider range of conditions and the project is obtaining seeds from a variety of sources to test suitability for Solomon Island lowland conditions.

Coffee is a high value, low volume product that is well suited to Small Island Developing States where the lack of infrastructure keeps transport costs prohibitively high. It is hoped that this initiative will allow smallholder teak growers to have an ongoing economic return from their land in a country where 85% of the population is rural and the chances for income generation are extremely limited.

Conclusion

While our trials have concentrated on growing teak, inter-cropped with flueggea. We are not claiming that this is the only mixture of species that would work and the decisions as to what is grown will be very dependent upon the smallholders themselves and on the soils and local conditions. There is a marked difference in the growth of both teak and flueggea when they are grown on coralline soils compared to the richer, volcanic soils of the major islands. Water-logged soils also affect the growth and timber quality of teak whilst making the trees susceptible to wind-throw as the roots cannot penetrate the water table.

Mahogany has been seen to grow well on coral soils and there are indigenous trees that will be adapted to a variety of conditions. Local knowledge will always be an important factor in the success of these ventures.