Fig. 4: Alternative ecosystem trajectories for Amazonian forests that transition due to compounding disturbances.

From examples of disturbed forests across the Amazon, we identify the three most plausible ecosystem trajectories related to the types of disturbances, feedbacks and local environmental conditions. These alternative trajectories may be irreversible or transient depending on the strength of the novel interactions¹⁵. Particular combinations of interactions (arrows show positive effects described in the literature) may form feedback loops¹⁵ that propel the ecosystem through these trajectories. In the ‘degraded forest’ trajectory, feedbacks often involve competition between trees and other opportunistic plants^85,90,92, as well as interactions between deforestation, fire and seed limitation^84,87,105. At the landscape scale, secondary forests are more likely to be cleared than mature forests, thus keeping forests persistently young and landscapes fragmented⁸³. In the ‘degraded open-canopy ecosystem’ trajectory, feedbacks involve interactions among low tree cover and fire⁹⁷, soil erosion⁶⁰, seed limitation¹⁰⁵, invasive grasses and opportunistic plants⁹⁶. At the regional scale, a self-reinforcing feedback between forest loss and reduced atmospheric moisture flow may increase the resilience of these open-canopy degraded ecosystems⁴². In the ‘white-sand savanna’ trajectory, the main feedbacks result from interactions among low tree cover and fire, soil erosion, and seed limitation¹⁰⁶. Bottom left, floodplain forest transition to white-sand savanna after repeated fires (photo credit: Bernardo Flores); bottom centre, forest transition to degraded open-canopy ecosystem after repeated fires (photo credit: Paulo Brando); bottom right, forest transition to Vismia degraded forest after slash-and-burn agriculture (photo credit: Catarina Jakovac).