Elephants had the habit of pushing trees into dongas [gullies]​—a strange habit, but one with an obvious element of self-preservation in it, for it helped block the dongas and so they filled up, and as the land scar gradually disappeared the veld flourished once more. And elephants also had the habit of pushing over thorn trees so that they littered the veld. But each fallen tree effectively protected islands of grass from desperate grazers in times of drought. These specially protected grass nurseries would often be the only grasses left after a really severe drought and would seed the veld when spring winds and rains came.”

Countries threatened by “desertification” have taken steps to halt the invading deserts. The people of Saudi Arabia have planted 10 million tamarisk, acacia and eucalyptus trees to save the al-Hasa oasis, near Hofuf, from the encroaching desert.