A lot of the "forests" we have at least here are planted monocultures which are periodically completely cut down. Also known as "tree farms". All trees are the same age. Also the forest is full of ditches that makes it hard to pass for animals. The ecosystem and the species living there are quite different to real more natural forests. Most people have never even been to a multi century old forest anymore. Also we get invasions of pests like Diprion Pini etc. But yeah it looks green from a satellite or even airplane.