C.J. Stigter

Wind protection in a hedged agroforestry system in semiarid Kenya

In semiarid Laikipia (Kenya) severe crop damage and loss of mulch material may be caused by south to south-easterly winds from June to September. Demonstration agroforestry systems which surround farms with live fences had some success in protecting crops, mulch and soil, but great care must be taken, because air may be channelled through or over them. For demonstration purposes, a deliberate gap was made in a two meter high Coleus barbatus live fence to study its effect on wind speed and damage to crops. The effectiveness of protection given by this hedge together with intercropped Grevillea robusta trees was quantified using electrical cup anemometers. The combination of hedges and trees gave protection to a maize/bean intercrop but the biomass distribution was not the most suitable one. This picture was complicated by variable wind direction and interactions between wind and the biomass of hedges and trees. The lowest efficiency of wind reduction occurred closest to the deliberate gap, where also the lowest protection by the Grevillea trees was found. South to south-easterly winds increased the gap effect and caused gradients in tree protection perpendicular to the southern hedge. This gave at times wind speeds even higher than outside the system. Only visually wind effects could be detected. Trees and hedges strongly competed with the crops if not root pruned.