Chapter 14 Plant biodiversity and environmental stress

Abstract

This chapter describes relationships between environmental stress and the reaction of plants thereupon. Plants might react to environmental stress on various levels: on the biochemical, cellular, or morphological scale, and at species or population level. The characteristics of organisms change with their size (allometric relationships), with their life history (and related allocation strategies) and with their functional evolution. We discuss in this chapter, what kind of information may be derived from the composition of the vegetation (species diversity and species abundance). We provide insights in the effects of environmental stress on biodiversity., e.g. shifts in communities, the loss of species and appearance of new species. These insight may contribute to the validation of environmental standards. Another aspect we have dealt with is the use of plants to track climate and land-use changes in history. The use of plants as a bioaccumulative indicator is not discussed. When using a bioindicator, it is particularly important to state clearly which stress factor it is supposed to be sensitive for. It is shown in this chapter, that the sensitivity of plants for, e.g., heavy metals is dependent on the combination of morphological, anatomical and phenological characteristics of the plant. Evergreen plants are far more sensitive than early spring green plants, while shrubs are more sensitive than trees and obligate annuals (therophytes) are more sensitive than facultative annuals. Dependent on the character states, plants, or plant parts, may be, and are, used as climatic indicators, e.g., life forms and leaf anatomy in relation to temperature, rainfall and atmospheric CO 2 , or as reliable ecotoxicological tools (rootlet growth in testing solutions; and as time proxies (e.g. tree rings). The composition of plant communities can deliver a lot of information about environmental conditions. Further the implications of the so-called Ellenberg approach are analysed. Changes in vegetation over time indicate changes in climate patterns, as the main biotic response to climate change is migration, to track optimal conditions for growth. The type of photosynthetic pathways (C 3 versus C 4 photosynthesis) and leaf anatomy of plants as indicators for climatic changes is discussed and coupled with atmospheric teleconnections like El Niño and its antagonist La Niña. A very interesting way of bioindication by plants is used by palynologists. Their use of plant remains as proxies for vegetation history and human influence provides information about the development of the present society, also from periods where there were no written sources. They show us what the world looked like in historic and pre-historic era. This latter work can be seen as assessments of early human impacts on the environment.