Lydick proved that permanent, well-arranged s and crop shelter belts are as much of an asset as barns or plows. They are as essential to agriculture … - Richard St. Barbe Baker

Felling big is dangerous work, especially when the tops of the mighty trees are entangled with creepers.

... during this expedition I was to trudge through sand wastes which had been my forest haunts when I had been in Africa thirty years ago. Here one could actually see all the process of degradation, from high forest through the stages of orchard-bush and savannah to drifting sand.
When the forest is cleared for farming or other reasons, the debris is sooner or later burned up. Here we were standing on land where the which had been accumulated over thousand of years had been destroyed in a single season.

The experience of the nomadic farmer was that he would find fertile land only in the forest and it was natural for him to make clearings, piling smaller bushes around the greater trees to fell them by burning. The provided rich fertilizer for a season's growth but the land exposed to the elements failed to retain its fertility. So, after reaping a few crops, the nomadic farmer would penetrate ever deeper into the virgin forest ...
The next stage in forest degradation is so-called orchard bush, with large trees widely scattered. Then comes a type of fringing forest, which in time will deteriorate into h. After that there is ever sparser vegetation and s, sometimes mobile but more often fixed; then follows the desert floor ...