Date Published: June 26, 2019
Publisher: Public Library of Science
Author(s): Sanae N. Hayashi, Pedro Walfir M. Souza-Filho, Wilson R. Nascimento, Marcus E. B. Fernandes, Rodolfo Nóbrega.
Mangroves play an essential ecological role in the maintenance of the coastal zone and are extremely important for the socioeconomics of coastal communities. However, mangrove ecosystems are impacted by a range of anthropogenic pressures, and the loss of this habitat can be attributed primarily to the human occupation of the coastal zone. In the present study, we analyzed the spatial patterns of land use in the mangrove of the Brazilian Amazon coast, and evaluated the anthropogenic drivers of this impact, using a remote sensing approach. We mapped the road network using RapidEye images, and human settlements using global data. The results of these analyses indicate that the Brazilian Amazon coast has a low population density and low rates of anthropogenic impact in most of the coastal microregions investigated, factors that contribute to the maintenance and conservation of the region’s mangrove. The study also revealed that the paved road network is one of the principal drivers of land use in the mangrove, whereas other factors, such as population density, urban centers, and the number of settlements are much less important. While the region has 2024 km of paved highways, unpaved roads (17,496 km) facilitate access to the mangrove, with approximately 90% of anthropogenic impact being recorded within a 3 km radius of these roads. While the network of paved highways is relatively reduced in extension, preventive measures are urgently required to impede any major shift in the current scenario, caused by the expansion of major development programs. The results of the study indicate that biophysical, economic, and political factors may also contribute to the reduction, stability, and development of one of the world’s largest areas of mangrove forest.
Mangroves play a fundamental ecological role in the maintenance of the coastal zone and have enormous socioeconomic importance for traditional local communities [1–4]. Mangroves offer many ecosystem services , such as the protection of the coastline from catastrophic and erosive events [6,7], conserving and recycling nutrients , and water regulation , in addition to providing shelter, refuge, and feeding resources for local animals . Mangroves also play a key role in human sustainability and livelihoods. The biodiversity of these forests is exploited by the human populations of tropical coastal-estuarine regions for their subsistence needs, including the harvesting of food and fuel wood, and the extraction of lumber for construction [11, 12]. The mangrove ecosystem is also among the world’s most dynamic and productive coastal environments , with a primary production equivalent to that of the tropical rainforest . One other service provided by the mangrove is its role as a carbon sink. This ecosystem is also among the tropical ecosystems that are the richest in carbon anywhere in the world . More than half of all mangrove carbon stocks are found in Indonesia, Brazil, and Papua New Guinea . Thus, mangrove forests have enormous potential for the marketing of carbon credits for the reduction of the emission of greenhouse gases , reinforcing conservation strategies and contributing to the mitigation of climate change [16,18].
The present study focuses on the different types of mangrove land use already described for the Amazon coastal region . Here, we considered land use as all human activities recorded within the mangrove, including the adjacent areas of salt flat (known as the “apicum” in Brazilian Portuguese), such as deforestation, roads, urban expansion, ports, salt works, aquaculture, and degradation. The term degradation herein refers to altered mangrove areas, with dead trees and few remaining individuals that still resist the dry and hypersaline soil exposed to high solar radiation . We selected nine anthropogenic drivers, which are expressed by factors associated with anthropogenic features including human population density, urbanization, infrastructure, and their location in relation to the mangrove that have a direct and/or indirect influence on mangrove land use (Table 1). The spatial analyses were based on the administrative microregions defined in the database of the Brazilian Institute for Geography and Statistics, or IBGE (https://downloads.ibge.gov.br/downloads_geociencias.htm). The data were analyzed at a microregional scale, given that the municipal-level data are inadequate for a comparative analysis, in particular because many municipalities have only an incomplete dataset. All the analyses described below were run in ESRI ArcGIS 10.4.
Within the study area, on the eastern Amazon coast, a total of 1648 occurrences (Fig 4,S2 Table) of mangrove land use, occupying a total area of 67.11 km2  were recorded. This is approximately 1% of the study area. The use of mangrove habitats is concentrated primarily in the Salgado microregion, in Pará, and the Western Maranhão Coast and São Luís Urban Agglomeration microregions, in Maranhão (Fig 4). Together, these three microregions accounted for 70% of the records of anthropogenic impact in the mangrove ecosystem. By contrast, the Guamá microregion was the least used, with only 1% of the occurrences, followed by the Castanhal (2%) and Belém Metropolitan microregions, all located in Pará (Fig 4). However, the latter two microregions had only very small patches of use, which may have made them less discernible. Only the Baixada Maranhense microregion lacked anthropogenic impacts altogether, and had a well-preserved tract of mangrove.
The present study provided a synoptic perspective on the different human activities that exploit areas of mangrove habitat on the Brazilian Amazon coast, and the anthropogenic factors that drive this process. This region is sparsely populated, with the exception of the Belém microregion, in Pará, and the São Luís Urban Agglomeration in Maranhão. This is reflected in the high level of conservation of the mangroves of northern Brazil, with the habitat in most microregions presenting low levels of exploitation.