Using Epiphytes as Bioindicators of Acid Rain
in a Sub-tropical Rainforest of Taiwan

Emilie Stander

Acid precipitation is becoming widely recognized as a serious problem in East Asia, particularly due to long-distance transport of atmospheric pollutants from China. As China continues its economic development into the future, this input of atmospheric pollutants is projected to increase, causing neighboring countries in East Asia, such as Taiwan, to be in excess of critical loads of sulfur dioxide (SO2). Epiphytic lichens have proven to be useful bioindicators of acid rain in Europe, so perhaps epiphytes in sub-tropical Taiwan can serve the same purpose. However, there is currently little knowledge about epiphytes in this region. My study set about to address these questions through three main investigations: 1) the study and characterization of long-range transport from mainland China of atmospheric pollutants responsible for acid rain by analyzing nine rain events at three sites from storms originating from different directions, 2) the census of vascular epiphytic ferns of the species Asplenium nidus L. and non-vascular bryophytic cover epiphytes in two sites in Watershed One of the Fu-shan Experimental Forest to establish a snapshot of biomass and abundance and the identification of abiotic factors which may be affecting growth patterns of these two types of epiphytes, and 3) the study of effects of simulated acid rain of varying acidities on photosynthesis, growth, and nutrient uptake of A. nidus in a greenhouse study.

Due to a near lack of usable data for storms coming over China, I was unable to evaluate China’s contribution to Taiwan’s acid rain problem; however, I was able to characterize trends in internal Taiwanese acid precipitation. I was unable to identify abiotic factors which might explain differences in abundance between my two study areas. However, my study did raise questions regarding the survivorship of juvenile A. nidus individuals at one site, particularly in relation to the greater vulnerability of juvenile epiphytes to acid rain. It was found that A. nidus tends to leach cations and take up anions in response to simulated acid rain and that these effects appear to lessen over time. Plants receiving the most acidic simulated acid rain treatment showed the most significant differences in changes in ion concentration and photosynthesis. Plant growth did not appear to be affected by varying levels of acidity. In some instances changes in ion concentration covaried with measures of photosynthesis and growth, suggesting that future studies should control for photosynthetic capacity and size of A. nidus individuals.

This study gives direction for future studies relating to issues of long-range transport of atmospheric pollutants in East Asia, abiotic and disturbance factors which may be affecting epiphyte growth in sub-tropical Taiwan, as well as the effects of acid rain on epiphyte nutrient uptake, photosynthesis, and growth.