Organic matter dynamics in beech and pine stands of mountainous Mediterranean climate area

Aboveground biomass, litter production and weight loss of litter due to dec omposition were monitored in two forest ecosystems in the Sierra de la Dema nda, Spain, a Mediterranean climatic zone, over a 3-years period. The two e cosystems were a mature beech forest (Fagus sylvatica L.) and a Scots pine plantation (Pinus sylvestris L.). The aboveground biomass was estimated by cutting and weighing seven trees from each site according to diameter class es, recording the categories of trunk, branches and leaves. The results ind icate a total biomass of 152.1 Mg.ha(-1) in the pine stand and 132.7 Mg.ha( -1) in the beech stand. The percentage distribution of biomass weight of tr unks, branches and leaves was similar in both forests. The higher biomass i n relation to DBH was estimated in the beech forest, which seems to indicat e that it would not be very suitable to reforest land that is appropriate f or beech with pine. The litter fall was 5 791 kg.ha(-1).year(-1) in the pin e forest and 4 682 kg.ha(-1).year(-1) in the beech forest, although variati ons from year to year were observed, mostly due to water stress in summer. Weight loss due to decomposition of litter was similar in the two forest ec osystems, apparently due to the similarity in rainfall distribution at the sites. Jenny's litter decomposition index (K) and Olson's litter decomposit ion index (K-0) were higher for the Scots pine stand than for the beech sta nd, K: 0.46 and 0.37, K-0: 0.82 and 0.59, respectively, and Jenny's leaves and Olson's decomposition indices were similar. (C) 1999 Inra/Editions scie ntifiques et medicales Elsevier SAS.