CARACTERIZAÇÃO DE CLAREIRAS EM ÁREAS DE MANGUEZAL NA BAÍA DE TURIAÇU, AMAZÔNIA COSTEIRA MARANHENSE

O estudo da dinâmica florestal e da formação de clareiras no manguezal é um projeto de longo prazo, conduzido na Baía de Turiaçu, Amazônia costeira maranhense. Propõe-se analisar algumas questões como o que acontece ao ecossistema manguezal após a queda de grandes árvores, sua recuperação ou substituição por outros sistemas ecológicos.  Foi estabelida uma parcela de 100 m x 50 m (0,5 ha) num perfil perpendicular à costa. Os resultados referem-se à caracterização das clareiras nos primeiros 3 anos de monitoramento. A parcela apresentou um bosque misto, maduro, com altura média de 22 metros.  Foram encontradas 2 clareiras, de forma quase circular, com comprimento de cerca de 20 metros, formadas pela queda de Rhizophora mangle, Linnaeus, 1753. As bordas das clareiras, constituídas por R. mangle L.e Avicennia germinans (L) Stearn 1958, caracterizam-se por uma zona de perturbação com parte das árvores inclinadas na direção do eixo de queda da árvore principal e porcentagem elevada de herbivoria. A complexidade das clareiras no manguezal é observada pela co-existência de fases distintas, como a fase clareira, propriamente dita, a fase madura (decomposição acelerada dos troncos caídos) e a fase de recuperação (ocorrência de inflorescências e de numerosas arvoretas).Palavras-chave:  manguezal, dinâmica de clareiras, Amazônia costeira.ABSTRACTCharacteristics of gaps in mangrove forests from baía de Turiaçu, Amazonian coast of Brazil.The study of gap formation in the Amazonian coastal area of Maranhão State, Brazil, is a long-term program which deals with questions as: what happens with the mangrove ecosystem after big trees falling down? Can the mangrove recover from the gap to the original stand or would it change in composition and/or structure? Can the mangrove  recover keeping the mangrove ecosystem or it could change to other systems? How many trees can be removed from the system without committing the whole ecosystem? The results presented in this paper refer to the characterization of gaps  in a  mangrove forest in the Amazonian coastal area for the first 3 years (2000-2002).  A plot  of 100m x 50 m was established and in a transect from the coast to inland. We evaluated the changes on mangrove ecosystem from the impact of fallen trees in mature stands with average tree height of 22 meters. It was found 2 gaps inside the plot, with 20 m an average length occur in the gap margins Rhizophora mangle Linnaeus, 1753 and Avicennia germinans (L.) Stearn 1958 and this is a zone of high disturbance  with some trees affected and broken and also high herbivory percentage. Within the mangrove gaps are complexes showing, at the same time, different phases: the gap phase itself, the mature (fast decomposition) and recovering phases (presence of flowers, seedlings and saplings). The main natural disturbances inside the stand are heavy storms during the rainy season (from January to July), high wind intensity and frequency during the dry, monsoon,  season (from August to December),Key words: mangrove dynamics, mangrove gaps, gap dynamics, Amazonian coast

STRUCTURAL VARIABILITY OF MANGROVE FORESTS IN TURIAÇU BAY, AMAZONIAN COAST OF MARANHÃO, BRAZIL

Structural analysis of mangrove  forests was carried out in Turiaçu Bay during 1997 and 1998. The study area is influenced by brackish to saline waters with the occurrence of Rhizophora mangle, Avicennia germinans, Laguncularia racemosa and Conocarpus erectus. The other two red mangrove species R. racemosa and R. harrisonii occur mostly in freshwater and oligohaline environments and were not included in this paper. It was measured all mangrove trees over 2.5 cm of DBH (Diameter at Breast Height), inside 26 plots of 30 x 30 m, in the right side of the bay. The sample sites were arbitrarily selected considering 3 mangrove types: fringe, riverine and basin mangroves. The results show high structural variability. Mangrove species may be present in homogeneous, monospecific stands or in mixed stands of 2 or 3 species. Tree height ranged from 2 to 20 m and DBH from 3 to 35 cm with estimated basal area ranging from 1 to 50 m2 /ha. Estimated tree density ranged from 200 to 2,000 trees/ha. The best developed stands were found in well flushed areas fringing the bay or along river margins. The less developed mangroves were found to be the basin type, in dried, sandy soils, in poorly flushed areas. The correlations between structural parameters were positive for tree height x DBH (r= 0.88), tree height x basal area (r= 0.87), and negative to tree density x DBH (r= -0.71) and tree height x tree density (r= -0.60). The most abundant and best developed species is A. germinans, followed by R. mangle. L. racemosa is less abundant as well less developed in structure than the others, independent of its location in fringe, basin or riverine stands. The high structural variability sets the fragility of mangrove ecosystems in Turiaçu Bay and the necessity of adjusting management techniques to achieve sustainable development.Keywords: mangrove structure, mangrove landscape, Amazonian coast, coastal ecosystems

Improving visual enhancement of mangrove areas in Baía de Turiaçu, Brazil, by using HSI transformation in Landsat 5/TM imagery

Uso da Transformação HSI em imagens Landsat 5/TM no melhoramento do realce visual de manguezais na Baía de Turiaçu, Maranhão, BrasilA aplicação de realce por transformação de matiz, saturação e intensidade  (HSI) sobre uma imagem Landsat TM 5 demonstrou uma melhora significativa na delimitação das areas de manguezal na Baía de Turiaçu, Maranhão. O realce HIS permitiu distinguir os manguezais das matas de várzeas e outros ecossistemas costeiros e terrestres, com um erro mínimo verificado pelas campanhas de verdade de campo. Na costa amazônica, o fato das árvores de manguezal terem reflectância próxima à de ecossistemas de água doce dificulta o seu mapeamento . A transformação HIS revelou um aumento significativo na qualidade do  realce visual, permitindo a delimitação de manguezais e outros ecossistemas associados como matas de várzea, marismas, campos e matas de terra firme. A limitação principal do método reside na dificulde em separar areas de solo exposto daquelas com vegetação muito esparsa.Palavras-Chave: Manguezais, análises de imagens satélites, Landsat TM, transformação de cor, matriz-saturação-intensidade. ABSTRACTA hue-saturation-intensity (HSI) image transformation applied to a Landsat 5 TM image significantly improved the delineation of the well developed mangrove ecosystem bordering Baía de Turiaçu, Maranhão, Brazil. We managed to distinguish between mangroves, freshwater swamps, and other coastal and terrestrial ecosystems with insignificant errors, as verified by ground truth observations. Satellite remote sensing is potentially a profitable tool for mapping mangrove resources in Latin America. The fact that mangrove trees have spectral reflectance signatures very similar to freshwater swamps and terrestrial vegetation has until now made satellite mapping of mangrove resources problematic. Transformed image improved the visual display of mangrove type and associated ecosystems, such as freshwater wetlands, salt marshes, terrestrial grass, and forest communities. The main limitation seems to be the difficulty in separating areas with different types of exposed soils and areas with little vegetation.Key words: mangroves, satellite image analysis, Landsat TM, color transformation, huge-saturation-intensity

Spectral characterization of mangrove leaves in the Brazilian Amazonian Coast: Turiaçu Bay, Maranhão State

Mangrove communities are tropical systems which have fewer species than tropical forests, especially in Latin America and display a single architecture, usually lacking the various strata commonly found in other forest ecosystems. The identification of mangrove communities by orbital data is not a difficult task but the most interesting challenge is to identify themselves by the dominant species. The first step toward that floristic identification is the spectral characterization of detached leaves. Leaves from four species of mangrove trees were spectrally characterized considering the Directional Hemispherical Reflectance Factor (DHRF) determined through radiometric measurements using an integrating sphere LICOR 1800 attached to a spectroradiometer SPECTRON SE-590. In the visible bands (0.45-0.69 µm) the button-shaped mangrove Conocarpus erectus was brighter and the red mangrove Rhizophora mangle was darker than the other two species which shows very close DHRF values. Otherwise the black mangrove Avicennia germinans and the white mangrove Laguncularia racemosa can be distinguished from one another in the Near Infra Red (NIR) region (0.76-0.90 µm and in this region of the spectrum the DHRF of C. erectus and R. mangle become very close

O SISTEMA DE PRODUÇÃO DO CARANGUEJO-UÇÁ Ucides cordatus (DECAPODA: BRACHYURA) (LINNAEUS, 1763) NA ÁREA DE PROTEÇÃO AMBIENTAL DAS REENTRÂNCIAS MARANHENSES, BRASIL

A captura do caranguejo-uçá Ucides cordatus é uma atividade significativa entre as populações que vivem em áreas de manguezais.. Este trabalho analisou o sistema de produção do recurso caranguejo no município de Cururupu. A captura de caranguejos para comercialização se restringe aos machos com  comprimento da carapaça variando entre 30 mm e 70 mm, média de 49,8 mm, e largura  entre 48 mm e 93 mm, média de 70 mm. A captura por unidade de esforço (CPUE) foi, em média, de 125 caranguejos capturados por homem por dia de trabalho, considerando uma unidade de esforço correspondente a 13 catadores. Registrou-se em Cururupu uma produção anual de 2.583 ton., obtida a partir de um número reduzido de catadores, implicando em uma baixa unidade de esforço. Esta produção considerável ocorre, provavelmente, em virtude dos manguezais serem ainda pouco explorados. Em Cururupu a produção é direcionada exclusivamente para a comercialização local ou subsistência, diminuindo a pressão sobre o recurso.  Acredita-se, com base nas informações geradas neste trabalho que a normatização da atividade é fundamental para a sustentabilidade do recurso, desde que inclua a comunidade em programas de orientação, educação ambiental e gestão participativa. A ausência do controle de produção referente à captura e comercialização do caranguejo-uçá, representa ainda o principal entrave para o conhecimento  da abundância e o fortalecimento de ações de gerenciamento deste recurso.Palavras-Chave: Cururupu, caranguejo-uçá, sistema de produção, pesca artesanal, manguezais.ABSTRACTThe production system of the mangrove crab Ucides cordatus (Decapoda: Brachyura) (Linnaeus, 1763) in the Environmental Protected Area of the Reentrâncias Maranhenses, BrazilCapture of the mangrove crab Ucides cordatus is an important activity for many traditional populations living in tropical coasts of the word. The mangrove crab Ucides cordatus is a valuable resource in many tropical coasts of the world.  Crab exploitation was analyzed in Cururupu county, Amazonian coast of Maranhão state, Brazil.  Captures are restricted to males with biometric measurements showing length variations from 30mm to 70mm, average of 49,8mm, and width variations  from 48mm to  93mm, average of 70mm.  It was found the capture per effort unity  of 13 crab catchers, with  125 crabs.day-1.catcher-1, corresponding to an annual production of  2,583 ton. In the study area crab resources are consumed by local population and sold at local markets. The results suggest that the present stocks are under low stress due to the effort of few crab catchers. However, environmental education and fishery policies are needed for a sustainable use of the coastal zone. The lack of controling and understanding the production dynamics concerning to gather and market activities is still the main problem for the managemente of the crab resource in mangrove areas.Key Words: Ucides cordatus, crabs, system of production, mangroves