Species constancy depends on plot size - a problem for vegetation classification and how it can be solved

• Question   While it is well known that species richness depends on plot size, it  is not generally recognised that the same must be true for constancy. Accordingly, many authors use varying plot sizes when classifying   vegetation based on the comparison of constancies between groups of plots. We ask whether the constancy-area relationship follows a general   rule, how strong the effect of plot sizes is on constancies, and if it  is possible to correct constancies for area. Location For empirical evaluation, we use data from plant communities in the   Czech Republic, Sweden and Russia.   Methods   To assess the potential influence of differences in plot size on   constancies, we develop a mathematical model. Then, we use series of   nested plot species richness data from a wide range of community types   (herbaceous and forest) to determine the parameters of the derived   function and to test how much the shape of the constancy-area   relationship depends on taxa or vegetation types.   Results   Generally, the constancy-area relationship can be described by C   (A)=1-(1-C-0)((A/A0)boolean AND d), with C being constancy, A area, C-0   known constancy on a specific area A(0), and d a damping parameter   accounting for spatial autocorrelation. As predicted by this function,   constancies in plant communities always varied from values near 0% to   near 100% if plot sizes were changed sufficiently. For the studied   vegetation types, a two- to fourfold increase in plot size resulted in   a change of conventional constancy classes, i.e. an increase of   constancy by 20% or more.   Conclusions   Vegetation classification, which largely relies on constancy values,   irrespective of whether traditional or modern fidelity definitions are   used, is strongly prone to distorting scale effects when releves of   different plot sizes are combined in studies. The constancy-area   functions presented allow an approximate transformation of constancies   to other plot sizes but are flawed by idiosyncrasies in taxa and   vegetation types. Thus, we conclude that the best solution for future   surveys is to apply uniform plot sizes within a few a priori delimited   formations and to determine diagnostic species only within these   formations. Finally, we suggest that more detailed analyses of constancy-area relationships can contribute to a better understanding of species-area relationships because the latter are the summation of the first for all species.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

Constancy-area relationship

Fidelity

Phytosociology

Presence degree

Scale dependence

Species-area relationship

Synoptic table

Syntaxonomy

Vegetation database

Biology

Biologi

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)