El Niño-related Factors Contributing to Forest Degradation and Determinants of Amazonian Lands Recovery

Amazon forests intrinsic defenses against fire outbreaks and spread have been challenged in the past decades by extreme weather conditions, such as drought, global warming and land use practices. These alterations are particularly relevant to vegetation and soil resistance to burn, potentially impairing Amazon enhanced properties as a carbon sink. The aim of this narrative review is to outline the factors that made Amazon lands prone to El Niño (EN) environmental threats, its consequences and the conditions that favor forest regrowth. EN drought was one of the most impactful events for these forests, in which an unexpected decrease in precipitation and elevated temperature gave rise to devastating wildfires predominant in the Northern and Central Amazon. Before EN-years, rainfall periods declined causing observable, although less pronounced alterations in soil moisture and accumulated water aboveground, along with gradual scarcity of water resources in vegetation. Short- and long-term impairment of carbon stocks will have an impact on Amazon forest biomes considering foreseen climatic adversities and related fire episodes. Until the end of the XXI century, in the worst COsub2/sub emissions conditions, Amazonian forest degradation might reach a proportion of 40%. Forest resilience to precipitation changes can be reflected in structural adaptative modifications in vegetation and cover lands as dry to wet seasonal transitions take place. Fire-effects on Amazon forests impel selective recruitment of tree species, in terms of survival and carbon accumulation abilities, in burnt lands sensitive to the number of fire incidences. Soil composition also presents distinctive components, as a result of fires when compared to undisturbed areas, suggesting vegetation and underground forest alterations in burnt sites. Predicted climate changes allowed the projection of forest responses under diversified conditions, in which the severity of drier periods and fires could be both overcome by certain vegetation species regrowth or a restrictive factor for forest survival, in the most harmful carbon emissions scenario expected in the last four decades of the century. Environmental regulations are needed to control deforestation minimizing its deleterious impact on forest biomass, carbon emissions and regeneration of the Amazonian biosphere. Governmental positions on previous mandates that overlooked the application of forest protection laws from environmental hazards have been related to toxic levels of carbon emissions, comparable to the damage that occurred during EN events. Social influence on this matter was also demonstrated by social media political comments that were associated with the incidence of fire episodes in the Amazon within a time-frame of up to one week.