Water and nutrient inputs in rainfall into natural and managed forest ecosystems in south-eastern highlands of Ethiopia

Abstract

The input of rain water to the forest floor and the composition of rainfall and throughfall water were monitored between October 2001 and September 2002 in a natural and two plantation (Eucalyptus globulus and Cupressus lusitanica) forests at Munesa, southeastern highlands of Ethiopia. The proportions of throughfall to annual incident rainfall that passed through the different forest canopies were 53% under Cupressus and the natural forest and 82% under Eucalyptus. Annual nutrients deposition by rainfall varied from 0.08kg ha−1 yr−1 for Mg to 3.79kg ha−1 yr−1 for Na. Wash-off of materials deposited on the canopy surface and leaching of intracellular solutes from the canopy resulted in an enrichment of throughfall fluxes in K, Mg, Ca and Cl relative to rainfall and varied among forest types, being highest under natural and Eucalyptus forests and lowest under Cupressus. Sodium, NO3–N, NH4–N, SO4–S and PO4–P fluxes in throughfall were depleted relative to rainfall, but the magnitude of net depletion was different for the different elements; highest for Na (3.87kg ha−1 yr−1) followed by NH4–N (2.85kg ha−1 yr−1) and lowest for PO4–P (0.42kg ha−1 yr−1). The amount of canopy uptake and leaching were generally low in the dry season and increased sharply towards the wet season.