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.
$\begingroup$ How can this be done without waiting for decades? What measurements should we make? $\endgroup$ Jul 28, 2015 at 8:39
1$\begingroup$ @DeerHunter, you might consider whether there's soil moisture near the surface year-round. Mature trees can draw up deep water, but seedlings need several years damp enough that they don't die. (Grasslands evolved when the climate got drier than it had been.) Forests can also make their landscape more hospitable to other trees -- e.g., successional forests after a big landslide -- but they need reasonably reliable water. $\endgroup$– cphlewisJul 29, 2015 at 4:28
$\begingroup$ @cphlewis - Your comment if converted to an answer will get my vote. (In particular if you include refs to most appropriate methods - GPR, TDR, ADR whatever suits this particular application best). $\endgroup$ Jul 31, 2015 at 12:26
$\begingroup$ It's not close enough to my day-to-day work for me to write an answer, I'm afraid, $\endgroup$– cphlewisJul 31, 2015 at 17:11