Litter fall, decomposition and nutrient release in three semi-arid forestsof the Duero basin, Spain

The production of litter, the weight loss dynamic of forest litter decompos ition, and the dynamics of bioelement loss during leaf litter decomposition were determined in three forest ecosystems located in a semi-arid zone of the Duero basin, Province of Zamora, Spain, over 2 years. The three ecosyst ems were a climax evergreen oak (Quercus rotundifolia Lam.) woodland, a par aclimax stone pine (Pinus pinea L.) forest, and a disclimax maritime pine ( Pinus pinaster Sol.) forest. The mean total production of litter in the oak forest was 2320 kg ha(-1) year(-1), quite similar to the P. pinea pine for est, at 2400 kg ha(-1) year(-1) and higher than that of the P. pinaster pin e forest at 1728 kg ha(-1) year(-1). Leaves and needles accounted for most of this total production (78, 89 and 96 per cent, respectively). No signifi cant differences were found among the different leaf decomposition processe s, except for the oak leaves introduced in the pine ecosystems. A relations hip between time (independent variable) and the remaining leaf weight was f ound, which followed a negative exponential curve, DM (dry matter) = A + B exp(-Ct). About 30 per cent of the weight was lost during the first 4 month s. This indicates that climate (semi-arid conditions) speeds decomposition in the short term. The decomposition indices were determined for leaves onl y and for total litter. Considering total litter and leaves separately, sev eral relations were established for K, K-o and K-d decomposition indices. K and K-o in natural conditions decrease in the following order: evergreen o ak > stone pine > maritime pine. The Q. rotundifolia woodland potentially r eturns a greater amount of N and Ca than both Pinus forests. A litter-bag m ethod was used for the determination of the dynamics of the decomposing lea ves. A progressive loss of P and Mg in the decomposing oak leaves and pine needles, and a sharp loss of K were observed: in contrast, a tendency to re tain N and Ca was also seen. Pinus pinaster forest had the lowest annual N and P returns.