NITROGEN AS A LIMITING FACTOR IN THE DEVELOPMENT OF BEECH FORESTS IN THE SIERRA DE LA DEMANDA (SPAIN)

The leaf nitrogen contents of beech growing in the Sierra de la Demand a are studied, relating the contents with other structural population characteristics. For this, different experiments were conducted: (a) T o analyze of nitrogen levels in shed leaves, in leaf biomass and in le aves decomposing on a test plot in the 'Tres Aguas' beech forest. (b) To study leaf nitrogen contents over a vegetative cycle in the above b eech forest. (c) To study the leaf nitrogen contents of thirty beech s tands in the Sierra de la Demanda located at different altitudes and c orresponding to three beech budding isophenes. Annual nitrogen accumul ation in leaf biomass was 79.4 kg ha(-1)yr(-1), of which 22.9 kg ha(-1 )yr(-1) return to the soil substrate through shedding and 2.1 kg ha(-1 )yr(-1) are actually incorporated into the soil. Nitrogen cannot be a limiting factor for the development of the beech stands studied becaus e all of them surpassed the leaf deficiency threshold. Only other fact ors such as those of the soil or silvicultural treatment have a decisi ve effect on the production of the stands studied. Study of the correl ations for leaf nitrogen contents and the structural population charac teristics explored reveals that leaf nitrogen was only slightly correl ated with the mean height of the trees at the plot.