Brazilian biodiversity is undergoing numerous attacks and misguided policies that aim to reduce protected areas (PAs) with the main argument of expanding agribusiness to improve the country’s economic performance. An example is the draft law (DL) 527/2016, which aimed to reduce approximately 70% of the Devonian Escarpment Environmental Protection Area (DEEPA), a large PA in southern Brazil, which hosts two biodiversity hotspot biomes. This study shows the possible downsizing damages to biodiversity and landscape by quantifying the size and connectivity of the vegetation remnants in the surrounding landscape concerning the degree of threat to the species that occur in both the Atlantic Forest and Brazilian Savanna domains. The DEEPA downsizing can affect natural savanna and Atlantic Forest vegetation area proposed by DL 527/2016 would fail in protecting 383 (56.82%) of the threatened species. Only three species evaluated as critically endangered, 13 classified as endangered, and 13 classified as vulnerable would be preserved; the reduction would also negatively affect essential ecosystem services and the quality of life in human populations. Furthermore, man-made fragmentation and habitat loss would jeopardize several biological and ecological aspects fundamental to biomes’ maintenance and ecosystem services. In addition to reducing this environmental protection area, it would cut taxes from the current PA and could affect its surrounding municipalities in southern Brazil.