Nature doesn't care whether Scotland has forests or not. Natural events can have catastrophic consequences on the environment. Ice ages and meteor strikes are pretty darn catastrophic. Invasive species were wiping out other species before humans came along (at a much lower rate). Any balance you see in nature will only last until something big enough happens to change it.

Humans have preferences about the environment we live in. When there are things we like and want to preserve, it's up to us to do something about it.