The role of environmental legislation and land use patterns on riparian deforestation dynamics in an Amazonian agricultural frontier (MT, Brazil)

Agribusiness expansion and intensification in Brazil have prompted an abrupt change in land use and occupation in the Amazonian agricultural frontier since the 1980s. Considering the increasing suppression of native vegetation, riparian areas represent an important tool for protecting ecosystem services and biodiversity. Although the effects of land tenure and land use on large-scale deforestation in the Amazon have been widely assessed, their roles on riparian deforestation remains poorly explored. Here we assessed two municipalities – Querência (QRC) and São José do Xingu (SJX) – located in an agricultural frontier of the Brazilian Amazon to explore the relationship of illegal deforestation in riparian areas and different types of land use and property-sizes, as well as the impact of the Native Vegetation Protection Law (NVPL, Federal Law 12,651/2012) on environmental compliance. Therefore, we developed a robust geodatabase using hydrographic, land use and land tenure data. Riparian areas protected as Permanent Preservation Areas (PPAs) were delimited and their land cover mapped for 2012 and 2018 using high spatial resolution satellite images and unsupervised K-means classification method. We also applied landscape metrics to analyze riparian PPA structure and dynamics. Our results indicated that NVPL was followed by a downward trend in the riparian vegetation deficits in all land use types and property-sizes, but it did not stop new clearings. Although riparian PPAs in minifundios (≤ 80 ha) and agrarian reform settlements tended to concentrate higher relative deforestation amounts, large-sized farms were responsible for most of the absolute extent of riparian deforestation in both years, accounting for 76–78% in QRC and 93% in SJX. They were also the main drivers of new clearings, for which account for 71% in QRC and 86% in SJX. The impact of land use on riparian deforestation was not homogeneous among properties, possibly reflecting different levels of technological investment and management techniques. In the so-called consolidated areas, in which the riparian PPA minimum width was reduced by NVPL, decreases in deforestation between 2012 and 2018 were lower. In these areas, vegetation coverage did not exceed 23% in any of the study areas. In the riparian PPAs that was not under consolidated areas, the vegetation coverage was of at least 85% of the area. Local environmental governance may also have affected the riparian deforestation dynamics, in which stricter monitoring and law enforcement lead to lower deforestation extents. Finally, landscape metrics revealed the importance of managing riparian areas at the landscape level, as local improvements did not necessarily result in connectivity gains.