Nitrogen as a limiting factor in the development of beech forests in the Sierra de la Demanda (Spain)
Santa Regina, I.
The leaf nitrogen contents of beech growing in the Sierra de la Demanda are studied, relating the contents with other structural population characteristics. For this, different experiments were conducted: (a) To analyze of nitrogen levels in shed leaves, in leaf biomass and in leaves decomposing on a test plot in the ‘Tres Aguas’ beech forest. (b) To study leaf nitrogen contents over a vegetative cycle in the above beech forest. (c) To study the leaf nitrogen contents of thirty beech stands in the Sierra de la Demanda located at different altitudes and corresponding to three beech budding isophenes. Annual nitrogen accumulation in leaf biomass was 79.4 kg ha⁻¹yr⁻¹, of which 22.9 kg ha⁻¹yr⁻¹ return to the soil substrate through shedding and 2.1 kg ha⁻¹yr⁻¹ are actually incorporated into the soil. Nitrogen cannot be a limiting factor for the development of the beech stands studied because all of them surpassed the leaf deficiency threshold. Only other factors such as those of the soil or silvicultural treatment have a decisive effect on the production of the stands studied. Study of the correlations for leaf nitrogen contents and the structural population characteristics explored reveals that leaf nitrogen was only slightly correlated with the mean height of the trees at the plot.
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