LAND EVALUATION FOR AFFORESTATION IN A SEMIARID ENVIRONMENT - THE MONTANE PLAINS OF THE CENTRAL HIGHLANDS OF NORTH YEMEN

In semi-arid environments, much land use depends on water harvesting from the upper members of soil catenas to support crops on the lower members. In the Central Highlands of North Yemen, an initial evaluation of land for forestry on the basis of a general-purpose resource inventory highlighted drought and frost as the main constraints, and identified over 150 potential forest species. Subsequent species elimination and proving trials revealed that, in the absence of data, the frost hazard had been underestimated; and under a water-harvesting regime the very stony, coarser-textured midslope soils are more suited to more species than the fine loamy soils of the footslopes because of their better infiltration and rooting characteristics. Conventional soil survey and land evaluation does not cope easily with small, scattered land units; especially where site performance is dependent upon the behaviour and management of upslope members of the catena. For field use, a site type key has been devised with a supplementary table to match suitable tree species with site type. This expert system makes use of cultural, vegetation, soil and landform features, some of which are unique to North Yemen. However, the principles involved should have general application.