Is this surprising considering that a tree is genetically programmed to pump water from the ground and evaporate it?
The ice age ended about 12,000 years ago. When it did the glaciers, which had moved down into the middle of the US and into Africa, started to melt. They supplied large quantities of water to the regions that are now desert. Some trees grew, because trees will grow where there is water.
Large lakes were formed and of course there was more rainfall because there was more ground water available to evaporate and cause rain.
After thousands of years had passed these glaciers receded and the water stopped coming, gradually, which caused the lakes(think great salt lake for one) to dry up and the trees to die, because without the ground water to keep the rainfall coming the trees were denied the moisture they need to grow.
This is how the Sahara and the mojave and the "great American Desert"(look it up) were formed. They were not formed by people cutting down the trees, they were formed because the glaciers were gone and they reverted to what they were before the glaciers came, low rainfall areas that can't produce much vegetation.
Flame suit on!