Análise em um Sistema de Informação Geográfica (SIG) das alterações na paisagem em ambientes adjacentes a plantios de pinus no Distrito do Estreito, município de São José do Norte, Brasil

Abstract

Localizado em uma extensa restinga litorânea na região costeira do Rio Grande do Sul, o município de São José do Norte caracteriza-se por apresentar uma das menores densidades demográficas do Estado e uma economia baseada na silvicultura, agricultura e na pesca. A retração do setor agrícola e pesqueiro a partir da década de 70 e a desvalorização das propriedades rurais resultaram em condições propícias para a expansão do setor florestal, representado principalmente pela exploração de pinus. Na região do Distrito do Estreito a maioria dos plantios em grande escala foi estabelecida sobre planícies arenosas próximas à praia. Foram analisados em um Sistema de Informações Geográficas dois cenários (1964 e 2007) e, a partir da elaboração de mapas temáticos e análise ambiental, constatou-se que os florestamentos de pinus quando implantados próximos à praia, podem ser responsáveis por alterações na dinâmica de ambientes costeiros como dunas, brejos úmidos, banhados, lagoas e campos. Na área de estudo, as plantações de pinus ocupam 1.581 hectares, estabelecidas sobre dunas transgressivas e brejos úmidos. Esses plantios próximos ao sistema de dunas podem ter interferido no processo de migração de dunas transgressivas em direção as lagoas e banhados, e também, barrado o transporte eólico lateral que alimentava planícies arenosas localizadas ao Sul da área de estudo, onde atualmente ocorrem brejos úmidos. O efeito de barreira causado pelos plantios pode ter resultado no represamento das águas do sistema de lagoas do Estreito, diminuindo o número de sangradouros. Essas alterações interferem nos processos naturais e podem causar a homogeneização da paisagem, fragmentação de habitat e perda de biodiversidade. Os resultados desse estudo podem contribuir para a gestão dos recursos naturais nas zonas costeiras. A identificação das alterações na paisagem caudas por intervenções antrópicas e a análise da dinâmica dos ambientes alterados pode servir de subsídio para o pranejamento das atividades e o manejo sustentável da áreas naturais.

Located in a long and narrow sandy spit in the coastal zone of Rio Grande do Sul state, the city of São José do Norte is characterized as having one of the lowest demographic density rates in the state, with the economy being based on silviculture, agriculture, and fishing. The decline of agricultural and fishing sectors in the 70’s and the devaluing of rural properties have resulted in perfect conditions for the expansion of the forestry sector, mainly represented by pinus harvesting. Such activity plays an important role in the city’s socioeconomy, employing over half of the labor force and contributing with 73% of its GDP. The Estreito region is quite diverse in ecological and environmental aspects. It presents a rich mosaic of environments formed by an important system of coastal lagoons, marshes, native forests, fields, humid slacks, dunes, beaches, and extensive pine forest. Most large-scale pine plantations have been established on sandy plains near the beach, and may be responsible for changes in environmental dynamics. The population increase, the settlement of significant urban centers, industries, portuary complex, the development of agriculture and fishing are historic features observed along the coastal areas worldwide. In recent decades, the pressure of use of coastal resources has increased significantly, which increased the conflicts of land use. This situation has led governments to invest more in programs for integrated coastal management (GCI) as a way to sustainably management. The landscape changes resulting from the interference of pine forests in the natural environment on study area, were analyzed in a GIS. The database for this study consisted of aerial photographs at scale 1:60.000 held in 1964, and a digital satellite image Landsat 5 TM, orbit point-221_082, spatial resolution of 30 m, 26/05/2007. Aerial photographs were scanned with 600 dpi resolution, grayscale 8 bit color and stored in bitmap (bmp). After processing and editing of aerial photographs and Landsat image, we constructed a mosaic of aerial photographs that represented the area of interest. All images were georeferenced using Resample module of IDRISI ANDES GIS, which performs a systematic transformation that gently “adjust” the image based on the known locations of a set of ground control points or using a georeferenced image base. Georeferencing was based on the SAD 69 datum, UTM projection system, observing the Cartographic Accuracy Standard (PEC). With two georeferenced images of study area (1964 mosaic and 2007 LANDSAT image ), a both were cut in the same proportions to make them exactly the same number of rows and columns and same spatial resolution. With the photo-interpretation and recognition of classes of landscape in field trips, the images was classified with the Cartalinx software. Were defined land use classes mapped in both situations (1964 and 2007). With the images properly scanned and georeferenced, conducted the analysis in the GIS IDRISI, where tools to reclassification and cross-examination, it was possible to analyze the time-space variation between different use classes mapped to the two situations analyzed (Map 1 - 1964 and Map 2 - 2007). The changes were quantified in acres and calculated data for GIS and digitally represented in tables. Examining landscape changes in study area using a GIS, it was found that the plantations near the beach may interfere with environments dynamic and characterization of the area where they are deployed. distribution of coastal creeks, contention of mobile dunes, habitat fragmentation, and biodiversity loss. The pinus forests occupy 1,581 hectares, mainly established over transgressive dunes and humid slacks. Approximately 1,500 hectares of Transgressive dunes and humid slacks were completely removed by these plantations, resulting in decreased of fauna and flora eradication. Those forests near the dune system may have interfered with the migration process of transgressive dunes towards lagoons and wetlands as well as blocked lateral aeolian transport which fed sandy plains located further South, where humid slacks currently are found. The barrier formed by the forests may have dammed up the waters in the Estreito lagoon system, thus reducing the number of coastal creeks. The same hipotesys made for increasing the level of the lagoons may be related to the marshes, wich are associated with the lagoon system and showed a significant increase in their area. Significant changes were observed in other environments, probably resulting from the interference of pine forest in the natural processes of coastal dynamics, such as transport wind, water flow and ecological succession. The results achieved have great relevance to coastal management and aims to contribute to the management of the activities according to its aptitude and restriction areas, thus fostering a more effective and sustainable management.