What is cordons pierreux?

Answer 1

Cordons pierreux is a French term which translates in English to "lines of stones". A cordon pierreux is a set of small (fist-sized) stones placed at intervals across a region of desert land that's subject to seasonal flooding. Even though we might think of deserts as dry, they're actually kept barren when too much water going too fast continues the process of erosion and prevents plants and insects from ever getting a foothold. It's not so much how much water there is as how it's distributed over time. The cordon pierreux changes that by slowing the flow of water just a little, enough that suspended soil and seeds have time to be deposited along the line. The barrier gets a little thicker, some of the seeds take root, and after a season or two you have a line of plants as well as stones, which slow the water and material even more and start to create a pocket ecosystem with insects and other animals. It doesn't take long before a section of desert begins to turn into an oasis of fertile farmland and forest, all because someone put a few stones in the right place. The technique is probably ancient but was recently resurrected and refined by a Burkina Faso farmer named Yacouba Sawadogo, and popularised on a National Geographic TV special. It's allied to another technique of digging strategic holes called "zai" and filling them with manure to further enrich fields. The real point is that small, extremely inexpensive techniques can make huge ecological changes in a short time.