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

Abstract

The fl oodplain 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 classifi cation method was used, generating distinct classes of vegetation between each
island. To evaluate the effi ciency of the classifi cation, 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 fi ve 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 classifi cation.