Nitrogen cycling in a mature mountainous beech forest

Abstract

The nitrogen cycle in a mature, mountainous European beech (Fagus sylvatica) forest in Greece was examined for two hydrological years, 2001–2002 and 2002–2003. Bulk deposition was 1383 mm in 2001–2002 and 2392 mm in 2002–2003. Winter temperatures were mild in the first year and low in the second year. Despite these climatological differences, the inorganic N inputs to the forest floor, by means of throughfall and stemflow, were quite similar for the two years, i.e. 12.4 and 14.6 kg ha yr. Litterfall production was significantly (p < 0.05) higher in the second year but the N amounts in litterfall did not differ. The ratio of N/P in foliar tissue did not change significantly in 2003 compared with ratio values in the last years. The N amounts used for the annual stem and branch increments are rather high preventing, in this way, some nitrogen from being recycled in the near future. The total soil N content to a depth of 80 cm amounted to more than 5000 kg ha, and the C/N ratio in the Oh horizon was approximately 15 but the beech forest did not appear susceptible to N leaching. The concentrations of ammonium and nitrate N in stream water did not reach high values reported in the literature, and did not differ significantly in the two hydrological years. The fluxes of inorganic N in throughfall plus stemflow were higher than those in stream water indicating N retention in soil. Another reason for N retention in the ecosystem is probably the large difference between N requirements and uptake indicating N deficiency. Despite the maturity of the beech trees, the low C/N ratio in the Oh horizon and the relatively high N content in soil, the forest can be considered to be neither saturated nor having reached a N saturation transition stage.–1–1–1