Past and present systems of exploitation of the espinal since the 1600's have
led to successive degradation of basic resources with inevitable decrease in
productivity. (In fact, virtually all traditional silvopastoral systems in arid
and semiarid lands worldwide are in a more or less serious state of decline
[Le Hou6rou personal communication 1989].
All of the currently predominant production systems based on the espinales
are of the 'mining' type, i.e. constant harvest, with no investment in
long-term improvement. To take as an example the most frequently encountered
system, the wheat-annual range system (section 4.2a), we see that every
five to ten years the agroecosystem is 'brought to its knees', so to speak,
when all trees are cut, the small amount of nutrients accumulated in the soil
are taken out in the form of a wheat crop, and overgrazing subsequently
recommences. Long-term, this combination leads to progressive degradation
of both soil and vegetation resources.