Distribution of throughfall and stemflow in multi-strata agroforestry, perennial monoculture, fallow and primary forest in central Amazonia, Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respe ctive plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence o f different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As the se processes influence not only the water availability fbr the plants, but also water infiltration and nutrient leaching, the understanding of plant e ffects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stem flow in a perennial polyculture (multi-strata agroforestry), monocultures o f peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuacu (Theobroma grandiflorum), spontaneous fallow and primary forest du ring one year in central Amazonia, Brazil. The effect on rain water partiti oning was measured separately for four useful tree species in the polycultu re and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resul ting in pronounced spatial patterns of water input into the soil in the pol yculture system. For two tree species, peach palm for fruit (Bactris gasipa es) and Brazil nut trees (Bertholletia excelsa), the water input into the s oil near the stem was significantly higher than the open-area rainfall. Thi s could lead to increased nutrient leaching when fertilizer is applied clos e to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm ( Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp. ). Interception losses were 6.4% in the polyculture, 13.9 and 12.3% in the peach palm monocultures for fruit and for palmito, respectively, 0.5% in th e cupuacu monoculture and 3.1% in the fallow. With more than 20% of the ope n-area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyrig ht (C) 1999 John Wiley & Sons, Ltd.