Rarity and sparseness in plant communities: impact of minor species removal on beta diversity and canonical ordination

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Prepared by François Gillet, Adeline Rouzet, Daniel Borcard and Pierre Legendre

Contrasting effects of the progressive removal of rare or sparse species on the biodiversity assessment of a vegetation dataset (dune meadows in The Netherlands). Credit to authors.

To disentangle the role of rarity (low regional frequency) and sparseness (low local abundance), we applied to six vegetation datasets a progressive removal of either the least frequent or the least locally abundant species. Beta diversity – a measure of heterogeneity in the composition of plant communities – decreased when more rare species were removed, whereas it increased when removing more sparse species. Model performance of constrained ordination – a method to explain species assemblages by environmental variables – increased only slightly when removing rare species, while it was negatively affected by the loss of sparse species. We conclude that rare and sparse species play a different role in vegetation analysis. Ecologists should pay attention to this difference in biodiversity assessment.

This is a plain language summary for the paper of Gillet et al. (2025) published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.70013).