ESTRUCTURA DEL MANGLAR EN EN EL DELTA EXTERIOR DEL RIO MAGDALENA-CIENAGA GRANDE DE SANTA MARTA , UNA ZONA TENSIONADA POR ALTERACIONES DEL EQUILIBRIO HIDRICO

Abstract

With the main purpose of providing a baseline for future evaluations of ecosystem changes as a consequence of the reopening of freshwater canals from the Magdalena River, the structure of mangrove forests of the Exterior Delta of the Magdalena River-Ciénaga Grande de Santa Marta (DERM-CGSM land several soil properties were quantified. Mangrove forests surrounding the lagoonal complex exhibit from low and almost null structural development (completely dead) to complex structures. Best structural development was found on Caño El Jobo (JOB) and Ciénaga de la Aguja (AGU) in the southwestern part of the study area. JOB showed only two mangrove species but individual trees exhibited large sizes. In ARA, on the eastern side of Ciénaga Grande, the three species were present and structural development can be considered intermediate with several individuals of large size. These three stations (JOB, AGU, ARA) still receive fresh water flow from either the Magdalena River or from rivers of the Sierra Nevada de Santa Marta. The areas most isolated from freshwater flow (stations on Ciénaga de Pajaral and on the western end of Caño Clarín) showed the lowest structural development of the vegetation and a large part of it completely dead. It is concluded \Y\a\ Avicenniagerminans is the dominant species in the study area. In general, Rhizophoramangle was only found on the edges of canals or lagoons and towards the western side this species was almost all dead. An inverse relationship was demonstrated between soil salinity and basal area, height and foliar area and a direct one between redox potentials and the same attributes. The low foliar area values of A. germinans in the stations with highest soil salinities reflect in part the "aggressiveness"of the environment in which the species lives and specially its response to the stress imposed by the difficulty of obtaining water from the soil.