Exploring changes in ecosystem service values in strongly human-impacted, contrasting agro-ecological environments

Evaluating the impacts of land-use/land-cover (LULC) changes on ecosystem service values (ESVs) is essential for sustainable use and management of ecosystems. In this study, we evaluated the impact of LULC changes on ESVs over the period 1982–2016/17 in contrasting, strongly human-impacted agro-ecological environments: Guder (highland), Aba Gerima (midland), and Debatie (lowland) watersheds of the Upper Blue Nile basin, Ethiopia. During the study period, the continuous expansion of cultivated land at the expense of natural vegetation (bushland, forest, and grazing land) severely reduced the total ESV by about US$58 thousand (35%) in Aba Gerima and US$31 thousand (29%) in Debatie watersheds. In contrast, the unprecedented expansion of plantations, mainly through the planting of Acacia decurrens, helped the total ESV rebound by about US$71 thousand (54%) in Guder watershed after 2006, after it had decreased by about US$61 thousand (32%) between 1982 and 2006. The reduction in natural forest area was the major contributor to the loss of total ESV in the study watersheds, ranging from a reduction of US$31 thousand (63%) in Debatie to US$96.9 thousand (70%) in Guder between 1982 and 2016/17. On an area-specific basis, LULC changes reduced the average ESV from US$560 ha–1 yr–1 (1982) in Guder to US$306 ha–1 yr–1 (2017) in Debatie watersheds. Specific ESVs such as provisioning (mainly as food production) and regulating services (mainly as erosion control and climate regulation) accounted for most of the total ESVs estimated for the study watersheds. In most cases the total and specific ESVs of the watersheds were negatively associated with the population growth, which in turn was positively associated with the expansion of cultivated land over the study period. In Guder watershed, however, ESVs were positively associated with population growth, especially after 2012. This resulted primarily from the conversion of cultivated land to plantations (predominantly with nitrogen-fixing Acacia decurrens trees) because of the farmers’ growing desire to rehabilitate degraded cultivated land while simultaneously generating income through the sale of charcoal from this fast-growing tree. Our results suggest, therefore, that future policy measures and directions should focus on improving vegetation cover through planting multipurpose trees such as Acacia decurrens to prevent future loss of ESV in the midland and lowland regions of the Upper Blue Nile basin and beyond. The data were exteracted from high resolution remote sensing images by producing multiple land use/land cover maps through ArcGIS 10.4 software.