Base cation leaching from the canopy of a subtropical rainforest in northeastern Taiwan

We examined base cation leaching from the canopy of a subtropical rainfores t in northeastern Taiwan. The forest is characterized by extremely low leve ls 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 3 0, 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, s uggesting that cation leaching is neutralizing acid precipitation. The subt ropical forest studied leached cations from the canopy 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 rainf all and high relative humidity. This continuous exposure to acid precipitat ion could cause more intense negative effects on the canopy of subtropical forests as compared with temperate forests exposed to similar pollution loa ds. We suggest that the low base status of subtropical forests growing on l ow base status soils may make them very vulnerable to the negative effects of air pollution.