The human impact in South America can be primarily seen in the destruction of the rainforest and the usage of the grasslands for ranching.
Because big portion of the South American continent is covered with rainforests, the countries are trying to boost their economies by using them, especially because there is lot of high quality, expensive timber for which there's big demand. Also, because of the growing population, more food is needed, so the rainforests are cleared in order to make space for the agriculture.
The grasslands are heavily used for ranching, and instead of them being dominated by wildlife, they are dominated by cattle, and that is disrupting the whole ecosystem.
