Unexploited potentials of trees outside forests: Catchment landscape restoration through homegardens in Upper Mahaweli Catchment in Sri Lanka

It is vital to explore the potential of homegardens as (HGs) one of the major Trees Outside Forest sources in the Upper Mahaweli Catchment (UMC) in Sri Lanka, to restore ecosystem services lost due to large-scale deforestation. Woody tree diversity of HGs was assessed using diversity indices in selected agro-ecological regions of UMC. Then biophysical, socio-economic and institutional factors affecting the tree diversity of HGs were assessed. Data was collected from woody tree species from a 500 random sample of HGs located in two major districts in UMC using a resource assessment survey coupled with a household survey. A multiple linear regression analysis was implemented with primary and secondary data, using the STATA software. A total of 64,163 trees were enumerated and 110 woody tree species from 38 families were recorded. Shannon index, Simpson index Margalef and Evenness index ranged from 1.51–3.21, 0.32–0.91, 2.06–8.76 to 0.34–0.71 respectively. The majority of Agro-ecological regions such as Upcountry Intermediate Zone–IU2, Mid country Intermediate Zone–IM3a, Upcountry Wet Zone–WU2b, Mid country Wet Zone–WM2a, WM2b and IM3c recorded high tree diversity. Comparatively high evenness recorded in agro-ecological regions of Upcountry Intermediate Zone–IU2, Midcountry Wet Zone–WM2a and Upcountry Intermediate Zone–IU3d., is due to the rapid spreading of exotic species. According to the regression model (R2–50%, p < 0.01), several factors affected positively and negatively on tree diversity. Tree diversity in the majority of HGs located in UMC was similar to some South-Asian tropical forests, indicating the high potential of HGs in the ecological restoration of degraded UMC landscapes. Therefore, incentive-based policy instruments should be introduced to enhance the tree diversity of HGs to restore ecosystem services and the ecological sustainability of the UMC.