Floods and droughts are key factors in the distribution of vegetation in large rivers. The topographic position in the floodplain is a synthetic indicator of habitat, because along the evolution of river, vegetation adjusted its distribution and abundance to floods and droughts. The amplitude of distribution in the topographic gradient is an indicator of tree resilience to hydrological variability. We postulate that each species has an eco-hydrological signature. We analyze the composition and distribution of the trees in a stretch of 180 Km in Alto Paraná (Argentina), downstream of the Yacyretá dam where we found significant differences in the hydrological regime when comparing the hydrograph before and after Yacyretá. We compared two surveys of vegetation: one before to the reservoir, in 1980 and another in 2014, twenty years after building of Yacyretá, using as an indicator the trees frequency curves, in the same places, with the same method. We were able to establish the response of the river vegetation to the alteration of the regime produced by the reservoir. Our results indicate that 20 years after Yacyretá, there were significant changes in the occurrence of species at each site and between sites at both ends of the study area. Disturbances in the pulse regime cause a new equilibrium in the landscape, in which some tree species are favored and others excluded. Engineering work that disturb the hydrological dynamics of large rivers can alter the distribution of riparian forests. In the same way, changes in vegetation are indicators of disturbances in hydrological dynamics, geomorphology and landscape functioning.

PIP 11220130100293CO (CONICET) and PI Q001-2014 SGCYT (UNNE) projects supported this contribution.