摘要
The objective of this study was to quantify forest cover changes in three watersheds (Gilgel Abbay (1,646?km2), Birr (980?km2), and Upper-Didesa (1,980?km2) of the Blue Nile Basin between 1957 and 2001. Four land cover maps were produced for each watershed for 1957/1958, 1975, 1986, and 2000/2001. Nine different types of land cover were identified, five of which were forest cover classes. Between 1957 and 2001, the total forest cover increased in Gilgel Abbay (from 10 to 22?% cover) and decreased in Birr (from 29 to 22?% cover) as well as in Upper-Didesa (from 89 to 45?% cover). The increase in Gilgel Abbay was primarily due to the expansion of eucalyptus plantations. Natural forest cover decreased in all three watersheds. Wooded grassland decreased by two-thirds, dry/moist mixed forests decreased by half, and riverine forests had disappeared by 1975 in Gilgel Abbay and Birr. Major deforestation had already taken place in the northern watersheds, Gilgel Abbay and Birr, before the 1960s and 1970s, while in the southern watershed, Upper-Didesa, much of the deforestation occurred after 1975. The southern watershed still remained by far the most forested watershed in 2001 despite the strong ongoing deforestation. The changes in forest cover could affect natural resource management, greenhouse gas emissions, water resources, and agricultural production including coffee production. The patterns of change are different in the three watersheds. We therefore recommend further studies of the local conditions and drivers of change as the basis for designing effective policy to halt further loss of natural forest, which offers a wealth of ecosystem services.