Publication details
Phytosociological data give biased estimates of species richness
| Authors | |
|---|---|
| Year of publication | 2001 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Vegetation Science |
| MU Faculty or unit | |
| Citation | |
| Web | http://www.sci.muni.cz/botany/chytry/JVS2001.pdf |
| Field | Ecology |
| Description | Large phytosociological datasets of three types of grassland and three types of forest vegetation from the Czech Republic were analysed with a focus on plot size used in phytosociological sampling and on the species-area relationship. The datasets included altogether 12,975 relevés, sampled by different authors in different parts of the country between 1922-1999. It was shown that in the grassland datasets, the relevés sampled before the 1960s tended to have a larger plot size than the relevés made later. No temporal variation in plot sizes used was detected in forest relevés. Species-area curves fitted to the data showed unnatural shapes, with levelling-off or even decrease in plot sizes higher than average. This distortion is explained by the subjective, preferential method of field sampling used in phytosociology. When making relevés in species-poor vegetation, many researchers probably tend to use larger plots in order to obtain species-richer relevés. They seem to do that because a higher number of species gives a higher probability of more diagnostic species being found in the relevé; in the Braun-Blanquet classification system such a relevé can be more easily classified. This behaviour of phytosociologists has at least two consequences: (1) phytosociological databases under-represent species-poor vegetation types or are artificially biased towards higher species richness; (2) the suitability of phytosociological data for species richness estimation is severely limited. |
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