CO2 emissions from forest degradation in Brazilian Amazon

In the Brazilian Amazon, forest degradation from August 2014 to July 2015 reached 111,477 km². The processes of forest degradation are still poorly understood, being a missing component in anthropogenic CO2 emission estimates in tropical forests. The Brazilian Amazon forest degradation is mostly associated with logging and fire, or a combination of both. In the last years, forest degradation has shown significant values, frequently higher than deforestation. In dryer years, such as 2015 and 2016, the total degradation area reached 142,000 km². The processes leading to degradation impact biodiversity, carbon stocks, and increase forest vulnerability to future burning. According to Rapaport et al. (2016), the type of degradation, its frequency, timing, and severity influence changes in the biomass. Therefore, to quantify the carbon emissions derived from forest degradation, it is essential to depict its pathways. This knowledge allows us to assess the impact of the different patterns of land cover changes in carbon accounting systems. The authors mapped and followed the evolution of polygons of logging between 2000 and 2015, leading to clear-cutting or forest regeneration using remote sensing techniques. Of the total area of 1,115,414 km² mapped in the Brazilian Amazon, 115,414 km² were converted into clear-cut deforestation, 93,414 km² were characterized as degraded forest, and 40,414 km² regenerated the vegetation cover. The authors traced degradation trajectories in the Brazilian Amazon from August 2014 to July 2015 to analyze the degradation dynamics based on Santos et al. (2015) and Kury (2016). Then, they adapted the degradation component of the spatially explicit INPE-MET model to represent biomass changes following degradation events and assess their impact in the carbon balance. The authors used the DETER system as their source of old-growth forest degradation information. The DETER system is an operational system that identifies old-growth forest areas exposed to forest fires and disordered selective logging. The system is a complement to the PRODES system, also developed by INPE, that identifies the total removal of vegetation (clear-cut deforestation) in old-growth forest areas. The mapping of the degraded areas is performed independently each year, without removing areas identified as degraded in the previous years from the analysis. Therefore, the DETER system allows assessment of areas that are in the process of regeneration after the degradation event, as well as those in which this degradation is recurring. Therefore, they can consider the information provided by the DETER system in a given year as the indicator of an on-going degradation process caused mostly by fire or logging activities, although some natural disturbance events cannot be differentiated from anthropogenic ones by the DETER product. The authors identified three degradation trajectories: * Degradation to clear-cut trajectory: areas identified by the DETER system in a reference year that ended up being fully cleared and converted, as detected by PRODES in any of the following years. * Multiple degradation events trajectory: areas under recurrent degradation, detected by DETER at least in two distinct years, but that was not fully cleared during the analyzed period. * Single degradation event trajectory: degradation polygons identified in the reference year that did not intersect with any other degradation or clear-cut polygons in subsequent years. Polygons identified as part of the trajectory were not considered for the following reference years to avoid double-counting. For example, a polygon observed by DETER in 2014 and DETER in 2015 is considered part of the 2014 multiple degradation events trajectory and discarded from the 2015 trajectory analysis. The authors used the INPE-MET model to estimate the CO2 balance for the Amazon region until 2016, considering the clear-cut deforestation and forest degradation processes. The INPE-MET model combines spatially explicit maps of land cover changes with a process-based model of carbon dynamics. The model estimates the carbon balance for the Amazon region, including the impact of forest degradation and clear-cut deforestation on the regional carbon balance. The results show that the degradation trajectories are an essential component of the regional carbon balance, and that the INPE-MET model can accurately estimate the CO2 balance for the Amazon region. The model results indicate that the degradation trajectories contribute significantly to the regional CO2 balance, and that the carbon emissions from forest degradation are a major component of the regional CO2 balance.