Rio de Janeiro plans to wall in several major favelas, in an attempt to prevent sprawl from wiping out the tropical forest, the Associated Press reports.
The article suggests that appoximately 205 hectares (506 acres) of Rio's urban rainforest were destroyed from 2005 to 2008, and says officials blame most of the destruction on the expansion of the favelas as more newcomers arrived from Brazil's interior. So the state government will erect seven miles of 10-ft-high barricades.
506 acres is a lot of land. I'd like to see the statistics on the expansion of major downtown favelas like Dona Marta, the one mentioned in the article, which is on a very steep hill overlooking the middle class neighborhood of Botafogo and doesn't have a lot of room to grow. And I'd like to compare that with the impact of development on the forest in the Barra de Tijuca (a wealthy district to the south) and the Baixada Fluminense, to the north.