The potentials of agroforestry in biodiversity conservation and sustainable development; a case of the Mt. Kenya region
Muriuki, John Njagi
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A study on agroforestry systems in agro-ecological zones of the Mt. Kenya region that are suitable for tea and coffee growing was carried out with the aim of establishing their potential for biodiversity conservation and sustainable development. Agroforestry systems and related socioeconomics data was collected using questionnaires and conducting on-farm observations while, biodiversity data was obtained using descriptive vegetational and faunal survey methods in randomly selected farms in each zone.Validity of biodiversity data obtained was determined using the program EstimateS Ver. 7.5. Tree species diversity in different zones was determined using Shannon Diversity Index (SDI) while, Sorensen Index (SI) of similarity was used to compare coffee and tea agro-ecological zones in different districts for biodiversity. Chi-square tests were used to determine site selection tendencies by mammals, birds and herpetofauna within farm sites under different agroforestry practices while, Pearson Correlation was used to establish if relationships existed between agroforestry trees and farmland fauna. Results of the study showed that agroforestry systems in the Mt. Kenya region are largely agrisilvicultural, and are greatly influenced by prevailing socio-economic conditions. The results for species richness estimates showed that biodiversity data obtained on tree species, mammals, birds and herpetofauna had a completeness that was above 50% and was therefore reliable. Out of all agroforestry trees enumerated on farms, 67.4% were exotics while 32.6 % were indigenous, with 56.6% occurring in the tea zone and 43.4% in the coffee zone. Analysis of variance showed that there were no significant differences in the number of indigenous trees in the coffee and tea agro-ecological zones. Comparison of indigenous with exotic species for all zones showed that the indigenous species were more diverse (Shannon Diversity Index 19.99) than exotics (16.11). The Shannon Diversity Index values for agroforestry tree species (indigenous and exotic) were higher in tea zones (18.83) than coffee zones (16.96). Tea zones had also more mammals, birds and herpetofauna species. Kirinyaga tea zone had the highest diversity of agroforestry tree species in the region while Embu coffee zone was the least diverse for both indigenous and exotic species. The ordination of pairing the zones together showed that combinations with the highest SI percentage (i.e. greatest similarity) for agroforestry trees were the Nyeri coffee zone versus Meru tea zone, while combination of zones with the lowest similarity were Nyeri coffee zone versus Kirinyaga tea zone and also Kirinyaga coffee zone versus Kirinyaga tea zone. Sorenson's Similarity Index indicated that there was relatively more similarity in agroforestry trees and faunal biodiversity within a cropping zone than between the zones. Analysis of variance (ANOVA) test results indicated that the tea zones had significantly more mammals (F=7.094, sig.= 0.037), than coffee zones. Site selection tendencies for mammals were low (X2 = 20.75, d.f. = 11, P < 0.005) for most sites, with over 50% of them occurring in farm sites under woodlots. Mammals species richness and abundance increased gradually from the coffee zone towards the tea zone. For birds, analysis of variance (ANOVA) test results revealed no significant differences (F= 0.801, Sig.= 0.405) in the number of birds observed in the tea and coffee zones and that they had strong site selection tendencies (X2 =3.16), d.f. = 11, P < 0.005), suggesting a high degree of specificity within agroforestry sites. A similar pattern was observed with herpetofauna. Pearson Correlation results showed that there was a significant positive correlation between the total number of trees and farmland mammals (r = 0.716, p = 0.05), birds (r = 0.705, p = 0.05) and herpetofauna (r = 0.846, p = 0.01) in the Mt. Kenya region. The study concludes that agroforestry has an ability to raise the capacity of farmlands to conserve more biodiversity. Biodiversity conservation in farmlands however, need planning so as to determine the kind of bioversity (flora and faunal) suitable for each area, and the kind of agroforestry system or tree species that biodiversity requires for longterm conservation and sustainability. This includes decisions on agroforestry trees to plant or retain, management or maintenance of structural and compositional diversity among other factors. This in turn requires cooperation of landowners or farmers.