Nutrient pools to the soil through organic matter and throughfall under a Scots pine plantation in the Sierra de la Demanda, Spain

Aboveground biomass, litterfall, leaf weight loss during decomposition, nut rient return and water balance have been estimated in a Scots pine plantati on (Pinus sylvestris L.) in the Sierra de la Demanda, Spain, a Mediterranea n climatic zone. The aboveground biomass was estimated by cutting and weigh ing seven trees according to diameter classes, recording the categories of trunk, branches and leaves. The carbon and nitrogen content in the differen t fractions were also analysed. The results indicate a total biomass of 152 .1 Mg.ha(-1). The litterfall was 5.8 Mg.ha(-1).yr(-1), although variations from year to year were observed mostly due to water stress in summer. Great er decomposition constants were obtained for total litter than for needle l itter alone. It is possible that the mean soil humidity was not a limiting factor in the decomposition process, which would be due to the distribution of rainfall rather than to the total amount of precipitation together with elevated temperature. The values of precipitation reaching the soil fluctu ated monthly, depending on the rainfall characteristics. Important fluctuat ions in concentration were observed for Ca2+ PO4-3-P, and NO3--N. (C) 2001 Editions scientifiques et medicales Elsevier SAS.