Woody vegetation cover on cleared areas in the Amazon Basin: temporal mixture mapping suggests a revised conceptual model of deforestation

The Amazon Basin is experiencing large-scale land use conversion from primary forest to pasture. While several land cover datasets map cleared areas in the Amazon, the percent cover of woody vegetation (trees and shrubs) in cleared areas and its association with clearing age, soil type, and geology is poorly understood, despite its importance for carbon emissions, biodiversity, land–atmosphere interactions, and monitoring of pasture condition. We used temporal mixture analysis on Sentinel-2 imagery from 2019 to map woody vegetation cover on cleared areas in Rondônia, Brazil. Binary woody vegetation masks were generated at 10-m resolution using a threshold of the evergreen endmember, with an overall accuracy of 84%. The age of clearing for each pixel was calculated from MapBiomas (Sousa and Davis, Remote Sens Environ 247, 2020) with a 2019 base year. We find little evidence of large-scale abandonment of pasture: most (53%) of the cleared area in 2019 was “clean pasture” (< 10% woody vegetation cover), 34% was “dirty pasture” (10–90% woody vegetation cover), 10% was forest (90–100% woody vegetation cover), and 3% was early stage clearing (> 10% woody vegetation cover, cleared 1–5 years ago). Recently cleared areas (1–2 years) had high (60%) woody vegetation cover, woody vegetation cover decreased with pasture age, and older pastures (20–34 years) had consistently low woody vegetation cover (25% on average). The commonly observed decrease in greenness with increasing clearing age, which is sometimes interpreted as decreasing grass health, was due in part to decreasing woody vegetation cover as pastures were gradually cleared over a decade. These results suggest modifications to existing conceptual models that describe clearing as a rapid process with high rates of secondary growth. We found a gradual and semi-permanent clearing of woody vegetation and proposed a revised conceptual model of deforestation dynamics.