Influence of Yacyretá dam on trees distribution in the Paraná floodplain

Abstract

Numerous contributions indicate that the distribution of trees in floodplains is determined by hydrological dynamics and that some plants are more tolerant than others to flood periods, however very little scientific information allows to link the regulation of the pulse regime by the dams with the impacts they produce on river vegetation. We assume that the frequency curves of the trees in the floodplain are a synthetic representation of the niche of each species with respect to the macrofactor that conditions their distribution. We compared two surveys of vegetation: one before to the reservoir -in 1980-, and another in 2014, thirty-fourth years after building of Yacyretá, in the same places, with the same method in a 175 km stretch of the Upper Paraná floodplain, downstream of the Yacyretá dam. Using as an indicator the distribution curves densities based on frequency of the dominant trees and its relationship with the hydrological regime we establish the response of the floodplain forest to pulsing regime in both periods. Our results indicate that during 34 years after Yacyretá, there were significant changes in the hydrological regime and in the occurrence of some species at each site and between sites. We found that selected species show changes in distribution after 34 years of operation of the Yacyretá reservoir, despite which we only found statistically significant changes in 40% of the species surveyed. The results of our study provide a criterion for the analysis of the impacts of hydrological regulation on the distribution of floodplain forests in large rivers.