Base cation leaching from the canopy of a subtropical rainfoerst in northeastern

Abstract: We examined base cation leaching from the canopy of a subtropical rainforest in northeastern Taiwan. The forest is characterized by extremely low levels of base cations in both canopy vegetation and in the soils. The rates of canopy leaching of K+, Ca2+, and Mg2+ were very high, representing up to 30, 35, and 190%, respectively, of the amount stored in leaves. The rate of H+ retention in the canopy was close to the rate of base cation leaching, suggest-ing that cation leaching is neutralizing acid precipitation. The subtropical forest studied leached cations from the can-opy throughout the year, unlike temperate deciduous forests, which are physiologically inert in the winter. The forest canopy of the subtropical forest we studied is impacted by acid deposition and fog throughout the winter because of frequent rainfall and high relative humidity. This continuous exposure to acid precipitation could cause more intense negative effects on the canopy of subtropical forests as compared with temperate forests exposed to similar pollution loads. We suggest that the low base status of subtropical forests growing on low base status soils may make them very vulnerable to the negative effects of air pollution. Résumé: Nous avons étudié le lessivage des cations basiques dans le couvert d’une forêt subtropicale ombrophile du nord-est de Taiwan. Cette forêt est caractérisée par des niveaux extrêmement faibles de cations basiques tant dans l