In Scotland, the Caledonian Forest has been cut down by humans. According to an unsourced Wikipedia article the tree line in Scotland is at 500 metre (it does not indicate the tree line elevation difference between southeast and northwest Scotland, which should be considerable). That means considerable areas are naturally bare, and therefore arguably less unnatural than the areas where forests have been cleared. When I pass through Scotland, is there a way to tell whether the spot I stand on had a forest before that was cleared, or that it is a naturally bare area?
Just by looking at a treeless region it would be difficult to know whether it was naturally treeless or whether the lack of trees was due to human actions. The history of the region would need to be known.
In Scotland, due to the extent of glaciation during the last ice age some of the ground was scoured, leaving bare rock when the ice finally melted.
With soil removed there is little opportunity for trees to develop deep roots and establish forests.
Loss of soil can result from natural causes and human actions. The area around Queenstown, Tasmania, in Australia is now denuded of trees due to a combination of logging and sulfuric acid rain from smelter fumes that killed the then existing trees followed by heavy rainfall washing away the soil from the steep terrain.
One of the best ways to tell if an area is naturally bare is to leave it allow for at least several decades so that no humans can do anything to it. If trees naturally return to the area, that area once was capable of having a forest. If trees do not grow, the area either never had a forest or it has been so badly degraded that trees can no longer grow there.
Despite the environment carnage experienced by Queenstown, Tasmania during the 19th and 20th centuries and the subsequent lack of soil, if left alone, trees will try to grow in the area.