Nutrient cycling in a natural beech forest and adjacent planted pine in northern Spain

Above-ground leaf biomass, leaf litterfall, leaf weight loss due to decompo sition, redistribution of leaf litter and C and N return to the soil, and s easonal leaf nutrient dynamics have been studied in the Sierra de la Demand a, Spain, a Mediterranean climatic zone. The tree species considered were a climax beechwood (Fagus sylvatica L.) at 'Tres aguas' and planted Scots pi ne (Pinus sylvestris L.) at 'La Rasada'. The above-ground biomass was estim ated by cutting and weighing seven trees from each site according to their diameter classes, recording the categories of trunk, branches and leaves. T he carbon and nitrogen contents in the different fractions were also analys ed. The calculated total biomass ranged from 132.7 Mg ha(-1) in the beech s tand to 152.1 Mg ha(-1) in the pine stand, and leaf biomass from 3.4 Mg ha( -1) to 7.0 Mg ha(-1) in the beech and pine, respectively. The C : N (carbon : nitrogen) ratio was greater in the pine forest leaves. The total litterf all was 5791 kg ha(-1) per year in the pine forest and 4682 kg ha(-1) per y ear and the leaf litterfall was 2917 kg ha(-1) per year and 2897 kg ha(-1) per year in the pine and beech sites, respectively. The annual mean amount of N returning to the soil substrate was 29.9 kg ha(-1) per year on the bee ch and 23.3 kg ha(-1) per year on the pine. Weight loss of leaf litter due to decomposition was monitored for 2 years in the two forest ecosystems stu died. The results indicated that weight loss was similar at the end of the experimental period in the two forest stands: 40 per cent in beech and 43 p er cent in pine. jenny's decomposition index (K) and Olson's decomposition index (K-O) were higher for the pine stand than for the beech stand. The dy namics of total C and N throughout the study period was similar on both exp erimental plots. The evolution of N in green leaves follows the same patter n in beech and pine stands. The highest leaf N concentration was observed i n the spring and summer months, during initial leaf growth. Thereafter, it decreased due to retranslocation during the period of leaf-fall in autumn.