By Iwona Dembicz, Jürgen Dengler, François Gillet, Thomas J. Matthews, Manuel J. Steinbauer, Sándor Bartha, Juan Antonio Campos, Pieter De Frenne, Jiri Dolezal, Itziar Garcia-Mijangos, Riccardo Guarino, Behlül Güler, Anna Kuzemko, Alireza Naqinezhad, Jalil Noroozi, Robert K. Peet, Massimo Terzi & Idoia Biurrun
Vegetation ecologists are generally aware that vegetation types can differ strongly in their plot-scale species richness (alpha diversity). But what about beta diversity? Beta diversity can be measured between vegetation-plots to denote heterogeneity of plots in a landscape, but it also can be quantified at fine grains, i.e. within vegetation plots. The exponent z of the power-law species-area relationship applied to nested-plot series is such a measure of beta diversity. Recently it has been demonstrated that it is a variant of multiplicative beta diversity, standardised by the ratio of the smallest and largest plot size (see the VegSciBlog post on this topic here).
Using more than 4,000 nested-plot series from a wide range of grasslands and other non-forest habitat types across the Palaearctic biogeographic realm from the GrassPlot database, we now tested whether fine-grain beta diversity differs systematically among biomes and vegetation types. While there was a large variation within most of the typological units, we found significant patterns. Generally, the explained variance increased, the finer the typological units were: For example, in vascular plants, biomes explained only 14% of the variation in fine-grain z-values, but phytosociological classes 50%. Among the biomes, mean z-values were particularly high in the Subtropics with winter rain (Mediterranean biome) and the Dry tropics and subtropics. Natural grasslands had higher z-values than secondary grasslands. Alpine and Mediterranean vegetation types had particularly high z-values whereas managed grasslands with benign soil and climate conditions and saline communities were characterised by particularly low z-values.
We propose a conceptual model that is able to explain how different environmental drivers, as well as species’ properties, jointly influence fine-grain z-values via mean occupancy (schema above). This model is able to explain the main patterns among biomes and vegetation types found in this study. It also illustrates the somehow counterintuitive finding that vegetation types with more sparse vegetation normally have higher small-scale beta diversity. We further provide the descriptive statistics (means, minima, maxima and quantiles) of fine-grain z-values per typological unit as an open-access file, which allows using them as references/benchmarks in other studies. Knowing which z-values are “normal” can allow assessing deviations e.g. by various disturbances or neophyte invasions.
This is a plain language summary for the paper of Dembicz et al. 2021 published in Vegetation Classification and Survey (https://www.doi.org/10.3897/VCS/2021/77193). The post was prepared by Iwona Dembicz & Jürgen Dengler.