8.  SOME AGROFORESTRY PRACTICES IN KENYA                   

8.14 Trees along streams and rivers

Spatial arrangement

River banks are prone to erosion if they are not well covered with vegetation. Furthermore many important indigenous trees are riverine, i.e. they occur naturally only or mainly along water courses. Thus vegetation along rivers is important both from an environmental point of view and for the production of special commodities, e.g. medicine or fruits. No particular spatial arrangement is called for.

Areas where the practice is relevant

Along all water bodies.

Establishment and spacing

Protection of the existing vegetation is the first priority. If there are already too few trees, protection of natural regeneration should be the second option to consider. If trees need to be actively planted or sown, priority should be given to indigenous trees since they are generally better conservers of water than exotics. (This is, however, counter to the desire to produce wood with fast-growing exotics.) Spacing will depend on species and purpose, but usually no large pieces of land should be put under trees. Hence, normally a few trees will be planted at selected places and a fixed spatial arrangement will not be relevant.

Figure 8.17 Stream-bank protection

Management aspects

As always, protection during regeneration is important with young trees. Other management steps will depend on the species and the purpose for which the trees are intended. Sites along rivers are often fertile and therefore are often used for growing vegetables. Pollarding and pruning can then be considered for minimizing shade.

Benefits

Protection of the water bodies and protection of the stream banks from erosion also reduce problems with siltation downstream. Products can be harvested from the vegetation along the streams and rare tree species can be preserved—a "gene bank".

Examples of species

Very many indigenous species can be considered. Examples of more-or-less riverine species in Kenya are Acacia albida, Acacia elatior, Acacia gerrardii, Acacia polyacantha, Acacia xanthophloea, Ficus sycomorus, Populus illicifolia, Garcinia livingstonei, Vitex doniana, Syzygium guinensee, Terminalia brownii, Phoenix reclinata, Phoenix dactylifera, Conocarpus lancifolius, Hyphaene coriaceae, Tamarindus indica and Trichilia emetica.