Forests burn. They all do. And if you stop them from burning, they burn hotter in the future. Forest generally burn undergrowth leaving the taller trees. But forests that have been saved from burning will eventually burn. And when they do, they will burn hotter, killing all the tall trees. So, leave the Amazon alone. Its doing what it should do, burn.
A basic fact of nature...of forestry. Yet so many leftists want to fight nature and prevent ALL fires. Little do they know that some plants actually rely on fires to spread seed, in addition to what you point out about underbrush.