Resilience of the Amazon forest to global changes: Assessing the risk of tipping points

The Science Panel for the Amazon is an unprecedented initiative convened under the auspices of the United Nations Sustainable Development Solutions Network (SDSN). The SPA is composed of over 200 preeminent scientists and researchers from the eight Amazonian countries, French Guiana, and global partners. These experts came together to debate, analyze, and assemble the accumulated knowledge of the scientific community, Indigenous peoples, and other stakeholders that live and work in the Amazon. The Panel is inspired by the Leticia Pact for the Amazon. This is a first-of-its-kind Report which provides a comprehensive, objective, open, transparent, systematic, and rigorous scienti fic assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development. increase with higher levels of climate change and/or direct deforestation/degradation. Priority areas for model-data integration are understanding the CO 2 fertilization effect, soil nutrient limitations, recruitment/mortality dynamics, plant functional diversity, and reducing uncertainty in Amazonian rainfall projections. Abstract Here we review and discuss existing evidence of ongoing changes in the Amazon forest system that may lead to resilience loss and the crossing of tipping points beyond which the ecosystem may shift persistently to an alternative state. Grounded on the theory of complex dynamical systems, we analyze the state of the Amazon forest and its potential trajectories in the 21 st -century, aiming to provide support for a sci-ence-based management scheme for enhancing systemic resilience. This review is based on five systemic tipping points for which there is evidence; four climate-related: (1) annual rainfall value below 1,000-1,500 mm/yr, (2) dry season length above seven months, (3) for Amazon lowlands, a maximum cumulative water deficit above 200 mm/yr, (4) a global increase of 2 o C on the equilibrium temperature of the Earth; and one associated with human-induced changes: (5) 20-25% accumulated deforestation of the whole basin. Evidence suggests that, depending on varying combinations of stressing conditions, disturbances, and feedback mechanisms, current forest configurations could be replaced at local scales by: (i) a closed-canopy seasonally dry tropical forest; (ii) a native tropical savanna state; (iii) an open-canopy degraded state; and (iv) a closed-canopy secondary forest. Local-scale forest collapses could trigger cascading effects on rainfall recycling, intensifying dry seasons and wildfire occurrence, and leading to massive forest loss at continental scales, particularly in the southwest of the basin. The probability of crossing such tipping points depends largely on heterogeneities across the system, including geological, physical, chemical, and cultural processes that influence connectivity and the likelihood of contagious disturbances. Biodiversity patterns were historically shaped over the past 60 million years by these processes and still today influence forest adaptive capacity and resilience. Thus, maintaining biodiversity is critical for enhancing resilience and reducing the risk of systemic forest collapse in the near future.