Multivariate techniques summarize large sets of data and present their major trends in a graphically simplified manner. This paper discusses ways in which these techniques can be used to correlate biostratigraphical data. Stratigraphically constrained cluster analyses, which highlight distinct zones, may be performed on a number of sections. These can be plotted together to provide a concise summary that allows sequences to be compared. Ordinations, such as principal components and detrended correspondence analyses, can be performed on several sections simultaneously to extract a new set of axes that represent the combined trends of various taxa. The first few major axes can be plotted against depth as 'biostratigraphical logs'; the rest can be ignored as insignificant variation or noise. Sections can then be correlated based on these logs, either manually or using procedures such as sequence slotting. These techniques have been tested using artificial data from Edwards (1984), consisting of taxa of known spatial and temporal ranges. Correlations between sections were found to match closely the true ages. Inconsistencies in the data, such as time-transgressive taxa, were isolated on one axis, allowing them to be removed or studied further.
ABSTRACT1. A revised classification scheme is described for standing waters in Britain, based on the TWINSPAN analysis of a dataset of aquatic plant records from 3447 lakes in England, Wales and Scotland, which is held by the Joint Nature Conservation Committee.2. Separate ecological descriptions of 11 distinct lake groups (A-J) are presented with summary environmental data, macrophyte constancy tables and maps showing their distribution. These lake groups include small dystrophic waters dominated by Sphagnum spp.; large, acid, upland lakes supporting a diversity of plant species, including Juncus bulbosus, Littorella uniflora, Lobelia dortmanna and Myriophyllum alterniflorum; low-altitude, above-neutral lakes with a high diversity of plant species, characterized by the presence of Potamogeton spp., Chara spp. or water-lilies and other floating-leaved vegetation; and coastal, brackish lakes, with macroalgae.3. The Plant Lake Ecotype Index (PLEX) is presented as an indicator of changing lake environments. PLEX scores reflecting the new classification scheme have been developed for individual plant species and lakes. Applications of the index are demonstrated.4. There is discussion of possible applications of the data collected and the resultant classification, in the context of the Habitats Directive, the Water Framework Directive and other conservation requirements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.