Regeneration of secondary forest following anthropogenic disturbance from 1985 to 2021 for Amazonas, Brazil

Following old-growth forest loss and subsequent land abandonment, secondary forest grows throughout the Amazon biome. For Amazonas, agricultural colonization was unsuccessful in many regions, leading to the regeneration of secondary forest and carbon storage under favorable climate conditions. Herein, the extent of regeneration in Amazonas and its timescale are investigated, including a granular analysis of its 62 municipalities, based on the MapBiomas dataset from 1985 to 2021. By 2021, 10,495 km² of secondary forest had grown, corresponding to 28% of the lost old-growth forest. After normalization for algorithmic differences, this estimate was 17%-38% lower than prior studies for Amazonas that used earlier versions of the MapBiomas dataset, indicating increased accuracy in landcover assignments for more current versions of the dataset. For the northeastern microregion, representing the 15 municipalities of economic and population dominance in Amazonas, the growth of secondary forest varied from 3.0% to 9.8% of the total land area. For the southern microregion, constituting seven municipalities adjacent to large-scale deforestation of Mato Grosso and Rondônia, regeneration of secondary forest constituted 0.4%-1.2% of the land area. For the remaining interior municipalities, the regeneration was 0.0%-1.9%. Among the municipalities, the median regeneration interval, corresponding to the duration between the loss of old-growth forest and the appearance of secondary forest, ranged from 2 to 7 years. The median regeneration intervals of the interior, northeastern, and southern microregions were 3, 4, and 5 years, respectively. Even as the secular trend of deforestation continues in the Amazon biome and encroaches into the southern border of Amazonas state, the results herein indicate a possible resiliency toward secondary forest for undisturbed land on a timescale of several years, at least for mixed pasture-forest landscapes of kilometer-scale heterogeneity and assuming that a favorable climate persists for regeneration even as global change occurs.