The hills of Rio were initially covered in lush tropical forest, but most of this was chopped down in the 17th century. When it was realised that this was causing severe problems for Rio’s water supply, as well as creating landslides, a reforestation project was begun, and over 100,000 trees were planted in the second half of the 19th century. Today, 120 square kilometres of replanted forest are a national park which is home to much wildlife and birdlife.