Rapid and Intense Declines of Forest Connectivity in the Amazon Arc of Deforestation Over Four Decades

The Amazon Arc of Deforestation is facing a silent decline in ecological functionality. Using four decades of high-resolution land cover data, we reveal a dramatic decline in functional connectivity across deforested areas in the Brazilian Amazon. Analyzing 40 targeted large-scale forest landscapes across Pará, Mato Grosso, and Rondônia, we quantified connectivity for key ecological processes-seed dispersal, pollen dispersal, and gap-crossing capacity of animals-using graph theory metrics. Between 1990 and 2020, the connectivity dropped by up to 50% in highly deforested regions, even when accounting for stepping-stones. Simultaneously, spatial modularity increased in nearly all study regions, in some by more than 25%, reflecting a more compartmentalized landscape structure. Forest fragment distances rose, and mean patch area fell sharply, compromising dispersal and potentially gene flow. Our results suggest a potential breakdown of spatial connectivity within the targeted zones of the Amazonian forests, except in the Western Pará region, where higher connectivity and lower modularity still prevail. Without urgent connectivity-enhancing strategies, even remaining forest patches may become functionally isolated, threatening the maintenance of biodiversity.