A methodology for the description of border hedges and the analysis of variables influencing their distribution: a case study in western Kenya

This paper presents results from a survey of border hedges on farmland in w estern Kenya. The survey covered 160000 ha of high potential land in easter n Siaya District and Vihiga District of western Kenya. The survey attempted to widen the knowledge of the typology, the biomass and the parameters inf luencing the spatial distribution of hedge types. Spatial analysis was used to delimit hedge type sub-regions (using cluster analysis) and to identify the variables influencing the spatial distribution of hedge types (using d iscriminant analysis). It is demonstrated that a complex association of var iables is influencing the subdivision of the two districts in hedge type su b-regions in which ethnicity, population density, area in woodlots and ecol ogical variables like elevation, rainfall and soil fertility are important variables. These variables are influencing each other and are responsible f or the contrasting situation in Vihiga and Siaya District. Border hedges ha ve similar functions in both districts (demarcation of land, to prevent cat tle from entering), nevertheless species composition and dimensions differ remarkably in both districts. Border hedges in Siaya District are poorly ma naged or not managed at all. In Vihiga District people are used to manage t heir hedges. Agroforestry techniques, for example techniques based on frequ ent pruning of border hedges, have a high chance in being successful in thi s district because no additional investment in labour or time is required. The spatial distribution in the amount of biomass is strongly correlated wi th the distribution in the per cent area ground cover of border hedges. Thi s means that secondary data on the area in hedges derived from aerial photo graphs can serve as a useful indicator of the biomass present. As a result, the most difficult part of the field survey, the destructive sampling for the determination of the biomass, can be eliminated, making general surveys considerably easier.