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Khaya is a fast growing tree, and can grow to a height of 100 feet, reaching three to five feet in diameter. It yields timber similar to mahogany, but the timber is heavier than mahogany. Khaya matures in mere 10 to 12 years, whereas mahogany requires 20 to 25 years. Unlike mahogany, Khaya does not shed leaves periodically. A young Khaya plant within its first year develops a deep root system that makes it a drought resistant plant. Because of this, it can be successfully cultivated throughout the low regions of the country, thrives in wet as well as dry regions, even in poor soils, but not near water.
Out of seven varieties of Khaya, the most valuable variety is Khaya Senegalensis, also known as the African Dry Zone Mahogany. Khaya timber has been exported from West Africa (Gambia) to Europe since the first half of the 19th century. In Africa, harvesting of natural Khaya has been so heavy, leading to threat of extinction. Khaya is considered a vulnerable species and has been included into the ‘IUCN (International Union for Conservation of Nature) Red List of Threatened Species’.
Khaya is extremely valued by the local Africans over the ages; Fulani herdsmen prune the tree during the dry season to feed leaves to cattle. In Africa, the bitter tasting bark is used for a variety of medical purposes; it is taken against fever caused by malaria, stomach complaints and headaches. It is applied externally to cure skin rashes and wounds.
Khaya for the furniture industry
Khaya wood is pale in colour compared to mahogany. The paleness has misguided the Sri Lankan saw mill owners and the furniture manufacturers, who consider dark timber to be valuable and pale timber to be of inferior quality. They seem to have forgotten that satinwood (now almost unavailable due to maturing age of 250 years) is pale in colour. With some harvested Khaya trees entering the market, some users have become knowledgeable.
When I harvested a 10 year old Khaya tree, the saw-mill owner was sceptical of the quality. But having sawn the logs, he was surprised by the hardness and difficulty encountered in sawing. Khaya timber with interwoven grains is harder than mahogany, sometimes tending to peel off during planing. Heavy fibre in Khaya gives it a springing effect and is used in boat building. Khaya timber is resistant to borer and termite attacks and is used mostly in the manufacture of furniture, wardrobes, flooring etc.
The fast growing Khaya, if popularised, can easily overcome the shortage of timber for the furniture manufacturers. Most furniture and timber products sold today are dyed anyway, and the paler colour of Khaya would not cause a problem in marketing.
Propagation
Similar to mahogany, Khaya is expected to produce flowers and seeds for propagation. The Forest Department had been importing seeds for their plants and I am not aware of locally produced seeds. I have nearly 10 Khaya trees, some over 12 years of age, but did not come across any fruits. Perhaps the local climate especially in the Western Province may be non-conducive for fruit formation. But for an interested investor, it should be possible to produce new plants by tissue culture, which would yield young plants exactly as the mother plant. But the process is slow and obtaining a plant ready to put on the ground may take two years.
Khaya grows in poor soils and could make good use of vast acres of abandoned lands in the dry zone, former forests, burned down, cultivated and discarded by the chena cultivators. Unlike some imported timber varieties introduced to the country, Khaya is non-invasive and does not harm the environment. The short growing/maturing period would certainly interest investor growers.
Commercial growing of Khaya
Khaya could be commercially grown in Sri Lanka for the timber-starved furniture industry, also as a base for dendro power. Khaya’s possible role in power generation is discussed below.
Helping carbon cycle
Many species of plants can be grown in degraded or scrub lands without requiring irrigation or fertiliser. Therefore, they can restore lands, leading to re-greening of the environment. The foliage can be used as fodder or fertile mulch, while plants such as gliricidia are nitrogen fixing. Branches of the trees (wood) could be used as biomass, feeding dendro based power generators.
Dendro based power generation is considered carbon neutral; as harvested plants would have previously absorbed the same amount of carbon dioxide as would be released to the atmosphere from the combustion with the completion of carbon cycle. Further, unlike fossil fuels, the emissions do not carry significant quantities of toxic pollutants like nitrous oxides and sulphur dioxides.
Dendro based power generation
There are two primary ways of converting biomass to electricity.
i. Gasification – where the biomass is converted to a combustible gas, used as fuel to run an engine generator.
ii. Steam Turbine – where the biomass is combusted in a furnace to produce heat, which in turn makes a boiler to produce high pressure steam, driving a turbine generator.
The process of dendro power generation consists of:
1. Cultivation of dedicated fast growing forests with high energy yields.
2. Regular harvesting of biomass from the forest using cropping techniques ie. The whole tree is not cut down, but pruned systematically.
3. Pruned branches are converted into a convenient size
4. The biomass is transported and fed into a furnace of conventional steam turbine/generator or fed into a gasifier to produce gas that could be burnt in an engine coupled to an electrical generator.
There are a number of thermal power generating plants currently operating in the country and supplying electrical power to the national grid; while some use rice husks, a majority use branches of fast growing, nitrogen fixing gliricidia tree. In India, Tamil Nadu alone, there are over 15 biomass power plants, with an installed capacity of 160 MW.
The gliricidia trees are commonly found in the rural countryside on boundary hedges, which yield branches 1 to 2 inches in diameter. Branches are harvested by local farmers with household tools and supply to the power generators. Dried gliricidia branch is a soft wood with pith and the energy yield is low due to lower density of the wood.
If Khaya be planted as a commercial crop, after the initial growth, weaker plants would be removed during thinning to allow room for better growing plants. In growing plants, branches from the main trunk need to be pruned regularly, to ensure a straight tree trunk yielding higher timber value. Plants removed during thinning and pruned branches would offer raw material for the power generating plant. When the trees have matured in 10 to 12 years, they could be cut down for timber and large volume of branches would be available. In sawing of logs, the waste too could be used. Thus unlike gliricidia, khaya could supply a larger volume of feeding stock to a power plant and also supply timber with a high value every 10 to 12 years.
Comparison with gliricidia
Harvesting of gilicidia is simple, as the plant is kept at a convenient height for harvesting of branches from the ground. The branches are simple and straight, without sub-branches. Prior to transporting to the factory, the branches are cut into small pieces, a simple operation. Gliricidia plants mature in two years and then continue to yield biomass without replanting.Harvesting of Khaya as a fuel-wood would be more difficult and will require a power saw to cut. The resulting wood needs to be converted into smaller particles or chips acceptable for feeding into the mill. Dendro based power generation was invented in Spain, when environmentalists objected to burning of olive branches, as an acceptable means of disposal of pruned branches. The energy value is the same for all biomass per kg at the same moisture content. Khaya having higher density would result in a higher energy yield compared to gliricidia, but exact quantities need to be worked out. Khaya has a high timber value, whereas gliricidia has none. Khaya has a tough leaf which does not rot easily, whereas gliricidia leaves rot easily and can be conveniently converted into compost or be fed to animals. Gliricidia is a nitrogen fixer and when cultivated with other crops help fertility, whereas Khaya in its fast growth discourages other crops.
Future of Khaya in Sri Lanka
It would be interesting to find out the reaction of wild elephants to Khaya leaves as food. If elephants reject Khaya, same could be cultivated along the electric fences on the jungle side for a width of few hundred yards. The result would be an effective barrier between the elephants and the complaining villages.
Considering power generation alone, gliricidia may be more convenient than Khaya. But when Khaya plantation is considered as a timber production unit which could be harvested in 12 years, with power generation as a by-product during the waiting period, additional income would pay for the maintenance.
The most productive model to be considered would be a mixed plantation, where a mix of Khaya and glircidia is grown. The density of gliricidia can be reduced annually as Khaya trees mature. The arrangement would yield an income from year 2 out of gliricidia and some fertility needed for the Khaya would be provided by the gliricidia leaves and also from nitrogen fixing roots.
Need for reserch
During the past few decades when Khaya was introduced into Sri Lanka, hardly any research had been carried out on propagation, growth and potential uses. More research into possible energy levels from Khaya, cost effective methods of converting branches into biomass and effective means of converting Khaya leaves into compost is needed. Basic research needs to be followed by a pilot project. Meanwhile, research is needed to produce planting material in a large scale. The Forest Department may have succeeded in producing local seeds or tissue culture methods need to be streamlined to facilitate large scale production of planting material for the needs of large plantations.
There are Khaya trees planted by the Forest Department by the road-sides of minor roads in the Kurunegala district. These trees are hardly pruned and yield poor timber value. If the department allows harvesting the branches for research purposes, the existing dendro based power generators in the area could create with a workable model.
Considering the excellent timber quality, the short growing period and usability in dendro-power generation, Khaya has an enormous potential as a commercial cultivation and demands far more attention from the researchers as well as the business community.
(The writer is a Chartered Civil Engineer graduated from Peradeniya University and has been employed in Sri Lanka and abroad. He was General Manager of State Engineering Corporation of Sri Lanka. He can be contacted on [email protected].)
