Traditionally, the use of indicator plant species or assemblages to detect the possible presence of metal-rich deposits. It is based on the principle of limits of tolerance; i.e., it assumes that only specialized species can withstand metal-contaminated soils. In practice, plant response may be confusingly more complex (e.g., plants may respond to low availability of essential nutrients rather than to high presence of toxic minerals), which makes such indicators unreliable. In modern use the concept includes the collection and chemical analysis of plant materials or soil layers, especially humus, in which metal ions may accumulate. It is a supplementary rather than a primary prospecting method. Geobotanical exploration can also be used to detect reserves of elements in the soil, because some species of plant accumulate particular elements. For example, certain Astragalus (Fabaceae) species accumulate selenium. See also limiting factor.
Subjects: Plant Sciences and Forestry — Ecology and Conservation.