Abstract

Due to construction of dams on the river channels has caused enormous social and environmental impacts in South American countries which have been associated with vegetation dynamics in many studies. However, factors governing the spatial changes of forestation in the floodplain after dams have not been explored extensively. A total of 72 segments of 9 rivers (12 dams) located in five Southern American countries (Chile, Argentina, Uruguay, Paraguay and Brazil) were studied. This study examined the interacting effects of dam, inflow and land-use patterns of catchment areas and other factors on downstream vegetation patterns along the downstream reaches of some South American rivers. Forest and herbs vegetation coverage areas of river channels after a dam and land-use catchment area patterns were obtained by the Google area calculator and aerial image analysis. Forest coverage was the highest just below the dams, and the ratio of forest cover decreased with distance from the dam toward the river mouth. Forest coverage ratio was found to decrease with an increase in dyke distance, number of inflows (r=?0.814, p<0.01) and water coverage ratio, and bare land in the river flood plain. However, a principal component analysis (PCA) showed that the proportion of bare land in the catchment area, the dyke distance of the river and the number of inflows or tributaries are the factors most associated with forestation among the studied parameters. As a result of local deviation due to the entrance of tributaries after a dam, the effects produced by dams on vegetation as well as forestation are gradually decreased towards the downstream. Though in some cases different land use types such as agriculture areas reduce forest area, their impact on forestation was insignificant.

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