Diversity and composition of agroforestry species in two agro-ecological zones of Rwanda

Abstract

This study delves into the diversity and composition of agroforestry species in Rwanda's Eastern Plateau and Eastern Savannah agro-ecological zones. Examining these systems across diverse landscapes is crucial for selecting species adapted to local conditions. We surveyed four landscapes with varying tree cover levels, using stratified random sampling to allocate 240 plots for detailed field inventory. We analyzed dendrometric characteristics of woody vegetation, focusing on plants with ≥ 4 cm diameter at breast height (DBH). Exotic tree species comprised over 75% of trees across all landscapes. Diversity indices indicated significant differences in plant communities between the Eastern Savannah and Eastern Plateau, with higher diversity in the former. Sørensen's similarity coefficient for woody species between the two regions showed a moderate level of similarity (approximately 53%). However, there was a significant difference in the equitability of on-farm tree species between the zones, suggesting non-identical distribution patterns. The most common and dominant tree species were Grevillea robusta, Mangifera indica, and Persea americana, primarily used for timber and fruit production. Most encountered trees were small and scattered, with nearly 80% having a DBH below 20 cm, highlighting the prevalence of young trees. The dominance of exotic species emphasizes the need for further research on their impact on agricultural biodiversity, informing sustainable land management practices in Rwanda and similar contexts.