The drivers and impacts of Amazon forest degradation

Approximately 2.5 × 106 square kilometers of the Amazon forest are currently degraded by fire, edge effects, timber extraction, and/or extreme drought, representing 38% of all remaining forests in the region. Carbon emissions from this degradation total up to 0.2 petagrams of carbon per year (Pg C year−1), which is equivalent to, if not greater than, the emissions from Amazon deforestation (0.06 to 0.21 Pg C year−1). Amazon forest degradation can reduce dry-season evapotranspiration by up to 34% and cause as much biodiversity loss as deforestation in human-modified landscapes, generating uneven socioeconomic burdens, mainly to forest dwellers. Projections indicate that degradation will remain a dominant source of carbon emissions independent of deforestation rates. Policies to tackle degradation should be integrated with efforts to curb deforestation and complemented with innovative measures addressing the disturbances that degrade the Amazon forest. Description Losing the Amazon The Amazon rainforest is a biodiversity hotspot under threat from ongoing land conversion and climate change. Two Analytical Reviews in this issue synthesize data on forest loss and degradation in the Amazon basin, providing a clearer picture of its current status and future prospects. Albert et al. reviewed the drivers of change in the Amazon and show that anthropogenic changes are occurring much faster than naturally occurring environmental changes of the past. Although deforestation has been widely documented in the Amazon, degradation is also having major impacts on biodiversity and carbon storage. Lapola et al. synthesized the drivers and outcomes of Amazon forest degradation from timber extraction and habitat fragmentation, fires, and drought. —BEL Two Reviews spotlight the threats of ongoing deforestation and degradation in the Amazon. BACKGROUND Most analyses of land-use and land-cover change in the Amazon forest have focused on the causes and effects of deforestation. However, anthropogenic disturbances cause degradation of the remaining Amazon forest and threaten their future. Among such disturbances, the most important are edge effects (due to deforestation and the resulting habitat fragmentation), timber extraction, fire, and extreme droughts that have been intensified by human-induced climate change. We synthesize knowledge on these disturbances that lead to Amazon forest degradation, including their causes and impacts, possible future extents, and some of the interventions required to curb them. ADVANCES Analysis of existing data on the extent of fire, edge effects, and timber extraction between 2001 and 2018 reveals that 0.36 ×106 km2 (5.5%) of the Amazon forest is under some form of degradation, which corresponds to 112% of the total area deforested in that period. Adding data on extreme droughts increases the estimate of total degraded area to 2.5 ×106 km2, or 38% of the remaining Amazonian forests. Estimated carbon loss from these forest disturbances ranges from 0.05 to 0.20 Pg C year−1 and is comparable to carbon loss from deforestation (0.06 to 0.21 Pg C year−1). Disturbances can bring about as much biodiversity loss as deforestation itself, and forests degraded by fire and timber extraction can have a 2 to 34% reduction in dry-season evapotranspiration. The underlying drivers of disturbances (e.g., agricultural expansion or demand for timber) generate material benefits for a restricted group of regional and global actors, whereas the burdens permeate across a broad range of scales and social groups ranging from nearby forest dwellers to urban residents of Andean countries. First-order 2050 projections indicate that the four main disturbances will remain a major threat and source of carbon fluxes to the atmosphere, independent of deforestation trajectories. OUTLOOK Whereas some disturbances such as edge effects can be tackled by curbing deforestation, others, like constraining the increase in extreme droughts, require additional measures, including global efforts to reduce greenhouse gas emissions. Curbing degradation will also require engaging with the diverse set of actors that promote it, operationalizing effective monitoring of different disturbances, and refining policy frameworks such as REDD+. These will all be supported by rapid and multidisciplinary advances in our socioenvironmental understanding of tropical forest degradation, providing a robust platform on which to co-construct appropriate policies and programs to curb it. An overview of tropical forest degradation processes in the Amazon. Underlying drivers (a few of which are shown in gray at the bottom) stimulate disturbances (timber extraction, fire, edge effects, and extreme drought) that cause forest degradation. A satellite illustrates the attempts to estimate degradation’s spatial extent and associated carbon losses. Impacts (in red and insets) are either local—causing biodiversity losses or affecting forest-dweller livelihoods—or remote, for example, with smoke affecting people’s health in cities or causing the melting of Andean glaciers owing to black carbon deposition. Credit: Alex Argozino/Studio Argozino