Avaliação estrutural de uma floresta de várzea localizada na área de influência da macrodrenagem, bacia do una, na região urbana de Belém Pará.

Abstract

The urban occupation trend in large cities in the Amazon is to reduce native vegetation areas, thus causing severe damage to the natural environment and health of the populations. In Belém - PA, Brazil, the municipal public policy in the form of the Macrodrainage Project added value to peripheral neighborhoods, mainly in low-lying areas. On the other hand, it provided new areas for civil construction and increased anthropic pressure on the remaining vegetation. This study aimed to assess the losses in tree cover in the arca of the Belém Municipal Ecologic Park and its surroundings as a strategy of urban and environmental planning. The forest tree species (BHC>15 cm) were surveyed in an arca of 44.06 ha about 2 km away from the Val-de-Cães airport. For the creation of the vegetation map, an orthophoto analysis was made of the aerial survey of the city of Belém (1998) based on charts from the Brazilian Institute of Geography and Statistics (IBGE) and of the topographic survey of the Metropolitan Development Company of Belém (CODEM). The data were treated using the Fitopac software and Excel spreadsheets. The species inventoried were classified according to taxa of family, genus, and species of adult population and natural regeneration. The data were split into three distinct areas according to similar characteristics. The results indicated three distinct physiognomic groups: The pioneer formations, which occupy large open areas with the predominance of weeds and open fields with aquatic macrophytes, for a total of 17.94% of the Municipal Park; secondary formations, consisting of vegetation typical of recently deforested areas, where the low vegetation accounts for 6.03% of the arca and the high, 2.95%; and formations with high-forest vegetation, which include floodplain forests at 65.36% of the total inventoried arca and dry-land forests at 2.89%, which shows the greatest pressures tend to be on high floodplain vegetation due to the exposure of those areas caused by macrodainage effects. The survey identified 3,160 individuais in the sample units in a total of 1.90 ha, containing 21 families, 42 genera, and 48 species. The families with the largest number of species were Arecaceae, Fabaceae, Clusiaceae, Mimosaceae, Caesalpiniaceae, and Lecythidaceae. The most ecologically important species, according to the IVI and IVIA, were Caraipa grandiflora (tamaquaré), Mauritia carana (caranã), Symphonia globulifera (anani), Calophillum brasiliensis (jacareúba), Virola surinamensis (virola), and Euterpe oleraceae (açaí). Dominance and abundance values observed were 29.51 nr.ha'1 and 1,783 ind. ha"1 in arca Al (contiguous areas), 30.01 nr.ha"1 and 1,723 ind. ha"1 in A2 (adjacent areas), and 31.18 nr.ha"1 and 841 ind. ha"1 in A3 (surrounding arca), which suggests this vegetation has the typical richness and diversity of estuarine floodplains of greater Belém. Taxonomic aspects reinforced by the Índices of diversity, similarity, and high degree of homogenicity may help manage silvicultures of those native species such as açaí, virola, and jacareúba, which are very abundant and dominant in the Park. It is concluded that the Park requires a management plan to ensure the permanence of plant and animal species that provide ecosystemic services (provision, regulation, cultural, and support) to the population in its surroundings and in greater Belém.