EFFECTS OF REDUCED WATER FLOW IN A RIPARIAN FOREST COMMUNITY: A CONSERVATION APPROACH

Abstract

Riparian forests promote several environmental services but are subject to many human impacts, for example, construction of dams. Dams reduce downstream water flow and directly affect riparian forests by the reduced outflow stretch. This study is one of the first works in the world which evaluated tree dynamics based on species annual rates of a riparian forest two and four years after reduction of water flow caused by dams. We hypothesised that several years of reduced river flow can alter the structure of tree community, reducing richness and diversity. We performed temporal soil moisture monitoring (at 0–10, 20–30 and 40–50 cm depth) to confirm reduction in soil moisture and tree community structure, richness and diversity (sampling trees with diameter at breast height ≥ of 4.77 cm) in 1.1 ha of forest. Three years after construction of the dam, soil moisture was reduced, especially in the dry season but tree richness and diversity showed no variation. However, in four years of study, the community dynamics had very high mortality rates (5.2% year^-1) and basal area loss (5.7% year^-1), demonstrating that water flow reduction had strong impact and severely modified the community. These changes were more intense in the understorey where generalists were better established. The water flow was reduced after dam construction and the forest would continue its changes, probably becoming structurally similar to a common seasonal forest.