Étude de la productivité des parcours de la zone d'Ain-Leuh (Moyen Atlas, plateau Central). II. Modélisation de la production d'herbe : interactions climats × sol × recouvrement arboré

A study of dry matter production in rough pastures of Ain-Leuh (Middle Atlas, central plateau). II. Model of herbage production: climate-soil-tree cover interactions. Herbaceous production was measured in 1983 and 1984 in the Middle Atlas and central plateau rangelands and grazed forests, in the Aïn-Leuh region, at 4 characteristic sites in 4 bioclimatic zones: semi-arid (Quercus ilex and Juniperus oxycedrus forest), sub-humid (pure Quercus ilex forest), and humid (Cedrus atlanticus and Quercus ilex forest, unsylvatic low grass at the highest site); measurements were made in areas protected from sheep and goat grazing, through 5 successive cuts from late February to mid-July, on plots varying in tree cover from 0 to 90%. Late February yield was mainly explained through the degree of precipitation occurring in both September plus October, interacting with the levels of soil nitrogen in poor soils of the Quercus and Juniperus zone, or level of rough sand in clay soils of the 3 upper zones. Yields from 4 successive cuts from the end of March to mid-July were mainly explained through interactions between radiative energy and a function of tree cover rate (100-R) eR/B; the B value was 50 in the semi-arid zone, and 90 for non-legume and 50 for legume plants in the sub-humid/humid zone). A climate humidity factor, the ETR/ETP ration in sub-humid and humid zone or the frequency of rainy days in the semi-arid zone, had an additive and an interactive effect respectively.