Chapter 12 The use of higher plants as bioindicators

Abstract

Various aspects of the (potential) use of higher plants as bioindicators are reviewed. Dependent on the scope of the enviromental analysis, many options for indicative as well as for causal identification of environmental disturbance and changes are possible at the level of individuals and populations of a species, at the level of plant communities and ecosystems. Ellenberg's indicator values give information on the qualitative relationship between the occurrence of a plants and its natural environment by highlighting several components of that environment, the indicator values for salinity and heavy metals are modified and improved. Quantitative analysis of such relations demands experimental testing. Bioindication has to consider the ecological differentiation and the selection of resistant ecotypes as a longterm natural process. Anthropogenic changes of environmental conditions can roughly be indicated by the disappearance of species (Red lists) without identifying the reason for this process. Evolution of resistant ecotypes is a good strategy of a plant population with a high genetic potential to survive in changing environments, but it camouflages the loss of non-resistant populations. Test plants can be used for localizing emission sources and effects of emissions or for aimed release of compounds either at acute or chronic exposure. Most tests, however, are developed for testing the acute toxicity of a compound, mostly without a well-defined selection and description of the cultivar, ecotype or variety of the plant species under investigation and without a proper conditioning of the accompanying environmental abiotic and biotic conditions, i.e. air humidity, nutrition, quantity and quality of radiation, temperature, and association with symbiotic organims. Endpoints of these tests range from germination up to a full lifecycle analysis in the laboratory or/and in the field partly accompanied with registration of visible symptoms. Phytometer, i.e. planting model plants in existing vegetation with or without isolation, can help to identify environmental processes within one or a few growing seasons. The pros and cons of a lot of approaches are highlighted.