I'm not going to spend a lot of time arguing this point on this list, but I will say that it would be much more difficult to determine from geological record whether a forest used to be a desert than whether a desert used to be a forest. This is because once a forest becomes a forest, the humidity and rapid decomposition of organic matter obliterates a lot of what was there before.
Deserts tend to preserve what was there before so people can dig it up.
Thus, one of the weaknesses of positivism. Or so I was told by a geologist. If an area has been clear cut and the soil then becomes heavily salted, the succession process for all intents and purposes has been thwarted. So the point was we most certainly create deserts, but rarely create forests to replace them. Right, there are no forests IN the Sahara.