Spatial heterogeneity of throughfall quantity and quality in tropical montane forests in southern Ecuador

Resumen

Canopy structure and throughfall (TF) were determined in three different forest types within the tropical montane rain forest belt in southern Ecuador. Heterogeneity of TF amounts and selected nutrient concentrations were compared to heterogeneity of canopy structure and tree species diversity. Canopy structure was characterized using hemispheric images and software calculating radiation beneath the canopy, mean leaf angle, and canopy openness. TF was sampled over a 1-year period (November 2001–November 2002), and analyzed for pH, electric conductivity, potassium, calcium, and magnesium. Radiation penetrating through the canopy ranged between 9.7% and 17.2% and gap fractions between 6.1% and 9.5% in the respective forests. At 71%, 85%, and 91% of incident precipitation, TF differed significantly between the three forest types, although standard deviations (SD) were high. The highest heterogeneity in TF (as represented by SD) was found for the forest type with the greatest heterogeneity in canopy structure, and vice versa. Heterogeneity of element concentrations in TF (again represented by their SD) exhibited strong correlations (r2 = 0.912–0.987) with tree species diversity per forest as expressed by the Shannon–Wiener diversity index. Rates of nutrient leaching from seven tree species were determined experimentally. Amounts of elements leached differed between species, and specific patterns were observed per species. These findings suggest that higher tree diversity leads to greater complexity in leaching patterns and to greater heterogeneity in TF nutrient composition. […]