Dynamics of dissolved nutrients in forest floor leachates: comparison of a natural forest ecosystem with monoculture tree species plantations in south-east Ethiopia

The dynamics of nutrients in water passing through the forest floors of two plantation forests (Cupressus lusitanica and Eucalyptus globulus) and an adjacent natural forest were monitored over a one year period at Munesa, Ethiopia. The results showed that, in all forest types, after K, Ca and Cl were the most abundant nutrients leached from the forest floor to the mineral soil. The concentration of N03−N in the natural forest was about 10 times higher than that of NH4−N, but 8 and 3 times higher than that of NH4−N under Eucalyptus and Cupressus, respectively. No significant differences in concentrations of most of the nutrients were observed among forest types, but magnesium and N03−N were significantly higher under the natural forest and Eucalyptus than under Cupressus. Except for NH4−N, which was depleted in relation to throughfall in the natural forest, the concentrations of all other nutrients were enriched in litter leachate in relation to both rainfall and throughfall. However, with the exceptions of NO3−N in all forest types, Ca under Cupressus and PO4−P under Cupressus and Eucalyptus, all measured nutrient fluxes from the forest floor to the mineral soil decreased in relation to throughfall fluxes. Generally, the results show that despite the differences in tree species composition among the forest types the organic layer acted as a sink for most of the nutrients coming via throughfall.