Ground vegetation as an indicator of ecological integrity

Abstract

Indicators are being sought for monitoring the ecological integrity of forests and other kinds of ecosystems. Biological measures are commonly used as indicators because of their inherent ecological importance and ability to provide insight into environmental change. Such measures are commonly based on data from sets of permanent plots in which the abundances of plant species are monitored. However, the data may be difficult to interpret, especially if corresponding information on natural and anthropogenic stressors is lacking. In this review, we examine general principles of indicator use and discuss the types of plot-based compositional measures obtained from vegetation that may be most relevant for monitoring ecological integrity. Our focus is on the ground vegetation of forested ecosystems, but the principles discussed are relevant to other vegetation types. Individual plant species, guilds, aliens, diversity indices, Ellenberg indicator values, the floristic quality assessment index, multivariate and multimetric indicators are examined, as well as concepts of threshold changes and the need for reference states. The usefulness of any given approach tends to be highly context specific. In particular, the value of using individual species as indicators is highly dependant on factors such as the character of the floristic community of interest and the types and intensities of anthropogenic stressors. Alien species are considered to be especially valuable indicators of changes in ecological integrity due to their established relationships with anthropogenic stressors, known historical state, relevance to all floristic communities, and ability to cause undesirable changes to biodiversity and ecological processes.