Biomass and nutrient content of a semi-arid mountain ecosystem:: the Juniperus thurifera L. woodland of Azzaden Valley (Morocco)

Among all the forest ecosystems those situated in semi-arid conditions have only been sparsely studied. In North Africa, these ecosystems are often degraded due to their economical importance in energy supply. In mountain woodlands this dependence on the tree is even stronger, like in the High Atlas mountains in Morocco. Because of the strong human impact that affects mountain tree species, and to prepare an efficient management of Moroccan forest resources, a clear evaluation is required of their biomass and nutrient content. It was in this scope that we studied the Juniperus thurifera woodland of Azzaden Valley (western High Atlas, Morocco), where these two parameters were estimated. The results presented here show that in spite of a strong degradation of the trees and severe climatic conditions, the aerial biomass is included in the brackets defined by other authors for this kind of ecosystem. The mean biomass was about 49 Mg ha(-1) with 95% of woody organs. The nutrient concentration (calcium, nitrogen, potassium and magnesium) for the different components shows that Ca much greater than N > K > Mg in trunks/branches, branchlets and leaves, and K > N > Ca > Mg in female cones. It appears that the strong concentration of calcium in all tissues (except in reproductive organs) participates in the neutralisation of top soil acidity through litterfall. The nutrient content study shows that Ca and N storage were significantly higher in trunks or branches (71.2 kg ha(-1) for calcium and 43.5 kg ha(-1) for nitrogen). For all elements, the nutrient content in leaves was significantly higher than the nutrient content in branchlets and female cones. (C) 2002 Elsevier Science B.V. All rights reserved.