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.

Understanding decomposition patterns of mixed-leaf litter from agroforestry species is crucial, as leaf litter in ecosystems naturally occurs as mixtures rather than as separate individual species. We hypothesized that litter mixtures with larger trait divergence would lead to faster mass loss and more balanced nutrient release compared to single-species litter. Specifically, we expected mixtures containing nutrient-rich species to exhibit synergistic effects, resulting in faster decay rates and sustained nutrient release, while mixtures with nutrient-poor species would demonstrate antagonistic effects, slowing decomposition. We conducted a mesocosm experiment using a custom wooden setup filled with soil, and the litterbag method was used to test various leaf litter mixtures. The study involved leaf litter from six agroforestry tree species: three species from humid highland regions and three from semi-arid regions. Treatments included three single-species leaf litter mixtures, three two-species mixtures, and one three-species mixture, based on the sampling region. Species included Calliandra calothyrsus (Ca), Croton megalocarpus (Cr), Grevillea robusta (G), Alnus acuminata (A), Markhamia lutea (M), and Eucalyptus globulus (E). Decay rate constants (k) were estimated using non-linear least-squares regression and observed mass loss was compared to predicted values for mixed-species litter treatments to assess synergistic and antagonistic effects. A two-way linear mixed-effects model was employed to explain variation in mass loss. Results indicate positive non-additive effects for leaf litter mixtures including nutrient-rich species and negative non-additive effects for mixtures including nutrient-poor species. The mixture of Ca + Cr + G had positive non-additive or synergistic effects as it decomposed faster than its corresponding single-species litter. Leaf litters with higher lignin content, such as A + M + E and Ca + Cr + G, exhibited less lignin release compared to what would be expected based on individual litter types, demonstrating antagonistic effects. These findings highlight that both litter nutrient constituents and litter diversity play an important role in decomposition processes and therefore in the restoration of the degraded and nutrient-depleted soils of Rwanda.

This study combines research on soil physical and chemical properties as affected by four Eucalyptus species in Ruhande arboretum. The soil samples for research properties were taken from 0-20 cm depth using auger and one undisturbed core from each sampling unit was taken for the analysis of soil bulk density. Soil bulk density and moisture did not differ significantly between all treatments. Sand proportions differed significantly only between E. tereticornis and E. maidenii whereas silt and clay were non-significant. The soil under Eucalyptus was sandy, with sand proportion ranging from 66.4-71%. Bulk density increased with increasing sand whereas moisture content showed a reverse trend. The soil samples for studying chemical properties were taken as described in Nsabimana et al. 2008. All chemical parameters except base saturation differed significantly between treatments. Soil pH was strongly acidic but rich in total nitrogen and organic carbon which was attributed to higher litter production, its relatively faster rate of decomposition, and greater amount of residues produced by the eucalypts. Carbon/nitrogen ratio, CEC, and BS were high under all treatments while the available phosphorus was lower which was attributed to the low pH. Future studies should test if the species similarly affect the soil or not and confirm if the species increase soil nutrients. Benchmarked study sites should be used to enable differences in the species effects on the site if any.

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.

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 34m intervals, leaving 25m on either side to avoid an edge effect. Along transects, circular 16m diameter plots spaced 20m apart were established, making a total of 56 plots. In each plot, woody species were recorded and those with heights >2m 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 5060cm diameter class and one Polyscias fulva was in the >90cm 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 1.897cm. The species importance value index ranged from 0.341.8 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 Simpsons 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.