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Effects of A. sieberiana trees on soil properties and plant diversity were investigated in Songa pastures, Rwanda. Tree characteristics and crown architecture of A. sieberiana were studied. Soil properties were assessed and plants were identified under and away from tree crowns. Counts of individual plants/species were done only under tree crowns. Nitrogen, P, and K were analysed in the soil, grass, and A. sieberiana leaves. Plant diversity was determined using Simpson's diversity index. Data were subjected to ANOVA. Soil organic carbon (SOC), cation exchange capacity (CEC), Ca2+, N and pH, and plant diversity were higher in soils under tree canopies than in open areas. Tree leaves were significantly richer in N and poorer in P and K as compared to grasses. Tree crowns grew wider and horizontal and developed intertwined secondary branching, reducing light intensity to as low as 38% under tree canopies compared to the open pasture. At 3 trees/ha stocking, A. sieberiana trees shaded 0.18 ha and herbaceous plants and grasses unpalatable to livestock dominated under tree canopies. A tradeoff of A. sieberiana tree value versus the loss of palatable grass due to tree presence needs to be assessed to decide whether the trees should be included in pastures and if yes, the apporpriate stocking identified.

Eucalyptus is abundant in Rwanda, mainly planted in short rotation woodlots, scattered in small clusters over the hilly landscape. A study was done in Butare and Busoro catchments, southern Rwanda from May to November 2007 to estimated water use of eucalypts in representative catchments in Rwanda, establishing a monthly water balance. We compared eucalypt water use to water use of other key crops in the study area and to that of eucalypts elsewhere. The woodlots had small coppice shoots ranging from 2 to 36 cm breast height diameter and potential tree transpiration recorded was 3 mm d -1 . The annual potential tree transpiration was 10 % below annual precipitation. Dry month water deficit observed could be covered by reductions in leaf area, stomatal closure and changes in soil water storage. A sensitivity analysis showed that 50 % leaf area reduction corresponded to potential tree transpiration decline of 32.8 mm. The deficit may not impact tree growth negatively since dry seasons are usually not active for tree growth. The moderate eucalypt water use rate observed in this study may be a function of trees' small size and low tree stocking since such woodlots had less potential transpiration. The observed eucalypt water use rate is smaller than the range reported for eucalypts in Africa and was also smaller than that of key annual crops in the study area. Managing woodlots as short rotations and increasing initial tree spacing may contribute to resolving issues related to catchment hydrology associated with eucalypt plantations.

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Agroforestry has the potential to contribute to the improvement of household livelihood, since its various forms offer multiple alternatives and opportunities to farmers. This study assessed agroforestry practice in Mukura sector, Huye district, Rwanda. A sample of 100 households was selected by stage sampling, randomly choosing four cells and two villages per cell in Mukura Sector. Face-to-face interview was dispensed to household heads, and data were collected on agroforestry practices, on-farm tree species, tree spatial arrangements, tree products, and the adoption rate. Woody species diversity and similarity were determined by using Shannon–Weiner diversity and Sørensen’s indices, respectively. Sixty percent of the farmers practiced agroforestry. Ten woody species were observed to grow on farm, providing varied products of timber, firewood, food and fodder, stakes for climbing beans, and income. Low adoption of agroforestry practice was reported resulting from small land, land tenure, ignorance, unavailability of tree seedlings, and the avoidance of tree-crop competition. On-farm tree diversity was observed to be higher than several other sites in Rwanda. The different cells of Mukura Sector grow the same woody species on the farms as demonstrated by reasonably high indices of similarity. We recommend that efforts be made to reinforce extension services to improve farmers’ awareness on the contribution of agroforestry to their social wellbeing. Ways of making seedlings available for planting should also be explored.

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This work studied the vegetation in a seven-hectare self-regenerated and protected forest about nine decades-old located in a previously cultivated site in the Ruhande Arboretum to identify woody species and their diversity. Ten parallel transects were established at 34 m intervals, leaving 25 m on either side to avoid an edge effect. Along transects, circular 16 m diameter plots spaced 20 m apart were established, making a total of 56 plots. In each plot, woody species were recorded and those with heights >2 m had their diameter at breast height measured. Phytosociological data including basal area, density, and frequency and their respective relative values were computed and used to determine species and family importance value indices within each plot. Across all plots, twenty-eight genera in 17 families were identified and 844 plants were recorded, including 755 trees and 89 shrubs, with most trees found in smaller diameter classes. Across all plots, only one Markhamia lutea tree was in the 50–60 cm diameter class and one Polyscias fulva was in the >90 cm diameter class. Of all woody species, Polyscias fulva was the most dominant since it had individuals with the biggest diameter. The number of individuals per family across all plots ranged from one for Cupressaceae, Dracaenaceae, Moraceae, and Solanaceae to 414 for Bignoniaceae. Across all plots, the diameter at breast height ranged from 1.8–97 cm. The species importance value index ranged from 0.3–41.8 for Nicotiana tabacum and P. fulva, respectively, while the family importance value index ranged from 0.2 for Annonaceae, Cupressaceae, Dracaenaceae, and Solanaceae to 41.6 for Araliaceae. Shannon and Simpson’s diversity indices were 1.772 and 0.707, respectively, while the evenness was 0.532, signifying that the forest was reasonably diverse. It is recommended that this forest can be conserved owing to its rich vegetation and to monitor its successional development.