4. THE ROLE OF TREES IN LAND USE

4.4 Trees for shelter and other structures

Construction

The need for timber and poles for construction purposes is one of the most common reasons for people to plant and grow trees in Kenya. Few indigenous tree species grow as straight as some of the exotics, and hence these exotic species have become very popular for building materials.

Eucalypts are commonly grown for poles since they are fast growing, straight, easily split and the wood is reasonably durable. In some areas, where the pressure on land is very high, farmers have, however, started to phase out the Eucalyptus since the trees are regarded as too competitive with crops. In such cases Grevillea is often found to be a good substitute. Grevillea has the advantage of not being very competitive and has timber that is well suited to sawing, hence it has more uses than Eucalyptus.

Figure 4.11 House construction

But with regard to resistance to decay and termite attack the best species are indigenous ones. Many indigenous trees produce wood that can last for many years without treatment with preservatives. Many exotic trees are also problematic in areas where termites are common. Seedlings of Eucalyptus and Casuarina spp. are very susceptible to termite attack, and Grevillea may also be attacked. In such areas it is still recommended to promote the use of indigenous trees for construction, but continuous efforts have to be made to ensure regeneration for a sustainable supply.

Figure 4.12 Pitsawyers at work

Shade

Trees provide shade, both for human beings and livestock. The shading characteristics of different tree species are very important in determining their suitability for different sites. In certain situations trees with a dense shade all the year round are desirable, e.g. in homesteads and at meeting places. In other situations a tree with less dense shade or a deciduous one might be preferable.

Figure 4.13 An Albizia gummifera provides generous shade for a community meeting place

Protection from wind

Strong winds can cause damage both to houses and crops. In a treeless landscape strong winds are often experienced, whereas an area with a lot of trees rarely has such problems. Trees around houses and schools are not only important for protection of buildings from strong winds, but they also improve the microclimate and add to the aesthetic beauty of the place.

Figure 4.14 A living fence with fruit trees provides a useful windbreak for a homegarden

Protection from animals

Trees or shrubs planted as live fences can effectively restrict the movement of cattle and thus provide protection for homesteads and other places from which livestock need to be excluded. Such fences can also provide protection for animals, e.g. for chickens against birds of prey.

Figure 4.15 Akamba farmers use a Commiphora hedge to provide a secure cattle enclosure

Marking boundaries

Trees are often used for permanent boundary demarcation. Often certain species are associated with this function, e.g. Croton megalocarpus and Commiphora zimmermannii subsp. eminii among the Kikuyu and Markhamia lutea among the Luo in Siaya. Machette.

Figure 4.16 Tamarindus indica used as a boundary marker with other fruit trees and a row of Grevillea robusta