Temporal Changes in Land Use Highlight the Vulnerability of Highland Grasslands in Protected Areas in Southern Brazil

ABSTRACT Protected Areas (PAs) are a primary mechanism to mitigate habitat loss, deforestation, and land‐use change. In Southern Brazil's Atlantic Forest, agricultural expansion has fragmented the Mixed Ombrophilous Forest and Subtropical Highland Grasslands, ecosystems with limited formal protection. Using the MapBiomas land use and cover time series (1985–2021), we quantitatively assessed changes inside and outside (500, 3000, and 10,000 m buffer zones) three federal PAs established in 2005. Our analysis revealed a contrast in conservation outcomes. Forest formations were effectively conserved within PAs, with losses of only −1.82% and −1.40% over 36 years in Araucárias National Park and Mata Preta Ecological Station, respectively. In contrast, the Subtropical Highland Grasslands ecosystem suffered a −31.08% loss inside the Campos de Palmas Wildlife Refuge, a PA specifically designated for their protection. Notably, this internal grassland loss exceeded a −30.28% loss in the broader 10,000 m buffer zone. Buffer zones consistently exhibited higher conversion rates and did not provide an effective conservation gradient, resembling the wider unprotected landscape. Although the PAs successfully stabilized forest cover post‐establishment, they failed to curb the conversion of grasslands to agriculture and silviculture. Our findings demonstrate that PA effectiveness is ecosystem‐dependent and underscore the urgent need for targeted conservation strategies, including active management and policy reform, to prevent the collapse of the threatened Subtropical Highland Grasslands.