Soybean Expansion in the MATOPIBA Region of Piauí, Brazil (1985–2024): Native-Vegetation Conversion, Overlap with Legally Protected Areas, and Implications for Sustainable Land Governance

Monitoring whether agricultural expansion advances over native vegetation and legally protected land is central to assessing the sustainability of commodity frontiers. This study reconstructs four decades (1985–2024) of soybean expansion in the MATOPIBA region of Piauí, Brazil, from annual 30 m land-cover maps, and quantifies its overlap with the protection instruments of the Rural Environmental Registry (CAR) and with strictly protected conservation units. The region holds 32.6% of the state’s territory but accounts for 41.1% of the gross loss of native vegetation recorded in Piauí. Only 23.7% of the 2024 soybean area was converted directly from native vegetation in a single annual step, yet 98.9% of it carried native vegetation in 1985, and the median interval between clearing and the first soybean season is three years: expansion over previously cleared land is largely expansion over land cleared in the preceding seasons. Resolving overlaps between declarations reduces the area under protection instruments from an apparent 40.2% of the region to a unique 34.5%. Soybean overlaps were declared Legal Reserves and Permanent Preservation Areas, unregistered land, and the Uruçuí-Una Ecological Station, where a 6001 ha complex occupies 4.6% of the unit and was confirmed against 10 m imagery. These indicate potential non-compliance to be verified, not adjudicated violations, and support anchoring deforestation-free supply-chain screening on the date of native vegetation loss.