For the novice the process of desertification is easiest to observe on rangelands with bunch grass ecology. The exposed soil between the grass is spreading, and you can watch it grow from year to year. You can watch the soil disappear and the ground become progressively more gravely, rocky and weedy. It is not climate change. The land is drying up and blowing away because there are very few new seedlings to replace the older grasses and forbs that naturally die out.
Many ecologists are familiar with the problem of the dying cottonwoods.
Cottonwood trees require periodic floods to initiate germination of new seedlings. Without floods there are no young trees to replace the old and dying ones. Look for it along the rivers where dams have altered the natural flood cycle. In controlled rivers you will typically find many old trees but few young ones. The problem on our rangelands is very similar.