Just back from Lanzarote where farmers make use of Cordons Pierreux to improve the land. It is interesting to note that there are three types of soil in Lanzarote, a yellow clay, a black cinder and a red gravel. The red gravel is used for planting well established palms and succulents. It seems to act as a barrier to weed growth.
The black volcanic ash cinder appears to be the favoured medium for farmers.
Lanzarote suffers from two key challenges, water and wind. There is little of the first and an abundance of the second. The dried out soil is easily blown away by the strong sea breezes that keep the islands cool.
Cordons Pierreux are stone ribbons that look like mini dry stone walls. Farmers use them to mar out field areas, or in some cases to protect individual plants. Some of them are very fancy, built tall and give good shelter to ornamental plants as in this photo. These are designed to protect delicate seedlings from harsh sea winds.
For the most part the Cordons look like these field versions:
To illustrate how they work I took the following close up:
This cordon bounds a field end, and you can see the vegetation is far thicker on the left than it is on the right. The prevailing wind blows from left to right. Small grains of soil are blown up against the cordon and fill the cracks in the stones. There they form a barrier to the soil moving. This barrier also slows the loss of moisture from this field. You can see (in real life) how the soil in the field is more moist that that outside the cordon.
Seeds blow into the cordon and germinate. Their roots and shoots help bind the whole thing further. They provide wells of biodiversity, home to native plants and a habitat for insects.
Cordons Pierreux don’t appear to be very sophisticated but in an environment such as this one they are a cheap, easy and incredibly effective solution to problems of farming.