Assessing drivers and prevalence of exotic and indigenous tree species in agro forestry systems around Gishwati-Mukura National Park,Ngororero District, Rwanda

Abstract

Agroforestry is promoted to reconcile agricultural production with landscape restoration, but its biodiversity benefits can be undermined when on farm plantings are dominated by a few non- native taxa. This study investigates why exotic species predominate in smallholder plantings and how institutional seedling supply, farmer priorities, and landholding structure interact to determine on farm composition around Gishwati–Mukura National Park. We used a cross- sectional mixed methods design: ecological inventories (36 plots) combined with household interviews, focus group discussions and non-farmer informant interviews in three cells- Gashubi, Bungwe and Cyahafi (of Ngororero District-Rwanda)- deliberately selected because they hosted major recent agroforestry interventions. The results have shown that exotic species accounted for 68.3% (313/458) of individuals, with Grevillea robusta alone representing 58.3% (267 trees), Persea americana 5.2% (24 trees) and other exotics 4.8% (22). Indigenous trees made up 31.7% (145 trees), dominated by Ficus sp. (12.0%, 55) and Markhamia lutea (9.8%, 45). Seedlings/saplings (<2 cm DBH) were only 8.5% of records (39 trees) and 71.8% of seedlings were exotic (28/39), indicating weak indigenous regeneration (28.2% of seedlings). Indigenous representation rose with plot size (small = 8%; medium = 24%; large = 32%). Farmers ranked exotic G. robusta highest for timber/profit (92%); 72% reported income from G. robusta within five years. Reported barriers to indigenous adoption included slow growth (67%), limited seedlings (58%), insufficient extension (42%) and low market value (33%). Institutional influence was strong: 65% of farmers said extension agents predominantly encouraged exotics, and MuLaKiLa-supported plots showed ~38% indigenous coverage versus ~18% in non- supported plots. These results indicate exotic dominance is a rational, constraint-bounded choice reinforced by supply systems. We recommend scaling indigenous germplasm supply, plot- specific extension and demonstrations, and market or incentive mechanisms to make indigenous trees viable for livelihoods while restoring biodiversity and erosion-prone highlands