Occurrence and spatial distribution of native acai groves in high-production areas of the Amazon region

Resumo

The floodplain forests of the Amazon estuary have undergone constant change over recent years, where management techniques, especially intensive management, have had an impact on the dynamics of the vegetation and land use. These changes can be monitored using satellite data. With this in mind, the aim of this study was to evaluate the dynamics of ground vegetation on the islands of Jarimbu, Mamangal, Itaboca, Mutirão and Buçu in the district of Igarapé-Miri, Pará, using images from the RapidEye and Planet satellites. The unsupervised ISODATA classification method was used, generating distinct classes of vegetation between each island. To evaluate the efficiency of the classification, an average of 200 random points were used, with another 30 points relating to the type of usage for each class. The Kappa index and overall precision were also analysed, in addition to calculating errors of omission and commission. Monitoring on a seven-year time scale using high-resolution satellites, a more than 50% increase in the Exposed Soil class was seen for the islands of Jarimbu, Mutirão and Itaboca, the latter responsible for an increase of more than 50% in the Urban Area class. On each of the five islands, the Alluvial class, representing the areas of açaí groves, has emerged over the last seven years, increasing in area at the expense of a reduction in the Arboreal class. In this respect, the confusion matrix showed a mean accuracy for the islands of ‘very good’, with a mean overall precision of 77.74%, and a mean Kappa index of 0.73, indicating strong agreement with the reference data and the classification.