Expansão de manguezais sobre marismas em resposta ao aquecimento global no limite latitudinal de espécies de mangue no Atlântico Sul

Abstract

There are now major uncertainties as to the direction and magnitude of mangrove salt marsh expansion due to climate change. The present study contributes to the partial filling of this gap in two ways - evaluating the latitudinal boundary of the South Atlantic; and using, unprecedentedly, dendrochronology in the understanding of the recent ecological processes involved in the mangrove response. The main objective is to evaluate the dynamics of the mangroves at Lagoon of Santo Antonio (Laguna - SC) in order to verify if they are expanding on the local salt marsh banks in response to the influence of climate change in the South of Brazil, latitudinal limit of species of mangrove in the South Atlantic. Five points of study were selected, represented by the occurrence of mangrove in association with salt marshes along its banks. Four plots of standard size of 25m2 were delimited for structural characterization of salt marshes (M and Mi), transition salt marsh/mangrove (T) and mangrove interior (I), in addition to obtaining dendrochronological samples and measurement of salinity interstitial and superficial. The analysis of the historical variation of the temperature occurred through data of anomalies of air temperature, made available by the National Oceanic and Atmospheric Administration (NOAA). The results for salinity can be considered intermediate, indicating that this is not a determining factor for the low structural development of Laguna mangroves. In relation to the salt marsh, Spartina alterniflora is the dominant specie, the nonparametric Kruskal-Wallis test did not present significant difference in the height of the salt marshes, which remained relatively constant between the plots, however, as the salt marsh was approaching the mangrove, there was a reduction of percentage of its vegetation cover. The species of mangrove that develops in the inner part to the marshes form mono specific forests of Laguncularia racemosa. Avicennia schaueriana occurs in the region, however, it presents few sparse individuals that were not captured by the plots. The biggest structural development was in the inner part of the mangroves compared to the Salt Marsh/ Mangrove transition and the non - parametric Mann - Whitney analysis indicated significant differences for mean height, mean and basal area. It was observed a process of recent colonization by seedlings and young of L. racemosa in the bank of salt marshes. Age analysis indicates that the transition is the youngest zone, with chronologyinitiated in 1991, and the interior of the mangroves in 1979. The data of positive air temperature anomalies indicate a tendency of elevation over the last decades, resulting in the increase of mean annual temperature of the region, and it proves to be a relevant factor for the physiology of mangrove trees. However, the low precision of the chronologies indicates greater uncertainty to the conclusions obtained, this imprecision is associated with the nature of the twisted trunks, resulting into a reaction to the wood and, consequently, interference in the rings of growth not related to external factors, such as the climate. In general, the results present strong evidence that mangroves are in the process of advancing on the salt marshes in Laguna / SC