Environmental assessment by plant indicators

Abstract

A number of plant indicators have been used in agriculture from early times because the vegetation reflects soil pH, soil moisture, soil fertility, etc. During the decades of 1960s and 1970s Japan has experienced severe environmental degradation such as air, water and soil pollution. Plant indicators, in those days, were considered to be a substitute for the physical and/or chemical measurement. Plant indicators practically used in those days were a visible injury to plants, a combination and/or diversity of epiphytes, aquatic plants and algae, a distribution of heavy metal resistant plants, etc. Environmental pollutants absorbed or adsorbed by plants, e.g., heavy metals, sulfur, fluoride, etc., have been considered as indices of environmental pollution. Dendrochronology was established, in the early years of the twentieth century in the U.S.A., to study past environmental changes. Although some pioneer studies on tree-ring information have been carried out in Japan, since 1920s, most of the early studies were not free from the dating error. In Japan, dendrochronology in the strict sense, was started in 1960s and has been rapidly progressed since 1970s. Besides environmental pollution, past natural disasters such as landslide, typhoon, and flood are also clarified by the dendrochronological studies. Another aspect of plant indicators is focused on future environment. Today, the decreasing biological diversity is recognized as one of the most serious global environmental problems. In this context, plant indicators in these days are not merely a substitute for the physical and/or chemical monitoring system but also the indicator for past environment and the goal of future environment.