DEVELOPMENT OF UTILITY AND LOCATION INDEXES FOR CLASSIFYING AGROFORESTRY SPECIES - THE CASE OF RWANDA

In a study of farmer knowledge and experimentation of trees and tree c ultivation, two categories of farmer consultants were identified, tree experts (n = 44) and control farmers (n = 70), via a two stage proces s of 'knowledge' ranking and community interviews conducted in three c ommunes in southern Rwanda in 1992. A detailed inventory of tree speci es was conducted revealing two key characteristics for on-farm trees: multiple utility and high locational flexibility. In order to logicall y organize the species inventory, two indices, a utility index (UI) an d a locational flexibility index (LFI), were developed. The two indice s were calculated for each species and then plotted as the axes on a b ivariate grid. While few species had both high bi utility and flexibil ity indices, the majority that did were indigenous species long used i n agroforestry systems (e.g., Euphorbia tirucalli, Vernonia amygdalina , Erythrina cihyssinicL1, etc.). A few naturalized exotics introduced in the 1930s (e.g., Grevillea robusta, Eucalyptus camaldulensis, E. sa ligna, E. maideni, Cupressus lusitanica and Persea gratissima) were al so appreciated for their multiple utility and locational flexibility. Farm sizes varied, averaging 1.27 ha among tree experts and 0.18 ha in the control group. The mean number of species cultivated was signific antly higher on tree expert farms (P < 0.01). However, tree density wa s much lower on tree expert farms (731 trees . ha(-1)) than on control farms (1,689 trees . ha(-1)). Competitive species were found primaril y on larger farms, whereas smaller farms were associated with species of greater UI and LFI. Farmers demonstrated deliberate and rational ch oices about which trees to plant in accordance with each species utili ty and flexibility in relation to land availability.