Farmland tree species diversity and spatial distribution pattern in semi-arid East Shewa, Ethiopia

Abstract

Information on tree species occurring in farming systems in semi-arid agroecologies is critical for sustainable land management, biodiversity conservation and informing food security interventions. The aim of the study was to characterize the species composition, diversity, structure and spatial distribution patterns of trees in the semi-arid East Shewa Zone of Oromia, Ethiopia. A survey of 172 land parcels with a total area of 76.09 ha, and belonging to 100 randomly selected farm households was conducted in 5 semi-arid sites in East Shewa. A total of 77 tree species belonging to 32 families were identified, and the Fabaceae were the dominant group. Trees were distributed differently in the four identified land uses (homesteads, line plantings, in crop lands and woodlots). Tree diversity was the highest in line plantings and the lowest in woodlots with the Shannon diversity index of 3.1 and 1.8, respectively. The majority (70%) of the species were native, whereas the remaining 30% were exotic. The average number of tree species per parcel was 4.7 ranging from treeless condition to 36 tree species in an exceptional farm condition. The height and diameter at breast height of the 6066 recorded individuals (2 m and above) ranged from 2 to 25 m and from 1 to 86 cm, respectively. The species Acacia tortilis, Eucalyptus camaldulensis and Acacia senegal were the three dominant species in the system. Correlation analysis revealed that land-holding size had significant positive relationships with tree species abundance and basal area, but not with species richness. Interventions are suggested for increasing the currently very low tree cover through planting and managing natural regeneration for improved farming system resilience in the face of climate change.