The briar is a bush that grows in all forests of the Mediterranean area, from Greece to Algeria including Italy, France, Spain and Morocco. This bush develops a ball-like root which is cut in blocks (plateau and ebauchons). After curing and drying, these briar blocks will be transformed in pipes by the pipe makers.
But not all briar is good for making pipes. During the long life of a briar tree many things can damage its root leaving only a rather small percentage of briar trees with a root good enough to make pipes from it.
In the second half of the last century tons and tons of briar trees were uproot. That intensive extraction of briar damaged many forests which will need a lot of time to recover. A briar tree must be at least 40 years old to have a root suitable for pipe making.
For the last decades, though, things have changed very much. The production of pipes has decreased a lot. Today the tendency is to have a smaller production of better quality, what reduces even more the percentage of suitable roots. Now it is not enough if the root is clean of woodworm, sand, stones, cracks, insects... in addition it has to be nice, and it must have straight grain.
Usually the older the tree, the better the root. But the soil characteristics and the weather also have influence in the root development. Generally if the tree grows in difficult conditions the root develops slowly and the grain is better. It is also important that the briar is not in an area too wet and/or too warm as it favors the appearance of woodworm.
To uproot the briar, cut the stem and clean the root from branches is really a hard job. It has to be made manually with the only help of a pick and a sickle. The briar collector first unearths a bit the root to see if it is big enough and appears to be good. If it does, he cuts the branches and the trunk. Then with the help of a pick he breaks the root branches and pulling what is left of the trunk takes the root out.
But the job doesn't finish once the root is out. It has to be cleaned of root branches, sand, small stones... which would be a danger for the cutters as explained in the next section.
In the end, the only way to know for sure the quality of a briar root is cutting it in two parts and seeing how the inside looks like. If we cut several roots of an area and realize that they are not good it is better to change the area. The opposite is also right; if several roots of an area are mostly good we are very likely to have found an area where most of the briar is usable.
But you never know until you try it.