Drivers of biodiversity depend on spatial grain and plant group: new paper from the EDGG Field Workshop to Bulgarian dry grasslands

Prepared by Jürgen Dengler & Iwona Dembicz

A thorough sampling of an “EDGG Biodiversity Plot” is a time-consuming and almost meditative procedure. Photo credit: Jürgen Dengler.

This Behind the paper post refers to the article by Dembicz et al. Drivers of plant diversity in Bulgarian dry grasslands vary across spatial scales and functional-taxonomic groups, published in the Journal of Vegetation Science (

Since 2009 the IAVS Working Group EDGG (Eurasian Dry Grassland Group) is conducting one or sometimes two research expeditions (“Field Workshops”) per year to study biodiversity patterns of grasslands in less well known regions of the Palaearctic biogeographic realm. This is done with a coherent methodology (Dengler et al., 2016), whose core elements are (a) multi-scale sampling of grain sizes from 0.0001 to 100 m², (b) multi-taxon sampling (vascular plants as well as terricolous bryophytes and lichens, sometimes also invertebrate taxa) and (c) extensive and standardised sampling of soil and other environmental data. Fourteen such Field Workshops have been conducted so far, starting with the 2009 expedition to study the dry grasslands of Transylvania, Romania, to the 2019 expedition in Armenia (Dengler & Biurrun, 2020), and most recently the ad-hoc (due to Corona conditions) 2020 expedition to study the subalpine and alpine open habitats of Switzerland. These sampling efforts so far have given rise to some of the world records of small-scale plant species richness (Wilson et al. 2012), led to the creation of the multi-scale plot database GrassPlot (Dengler et al., 2018) and the first comprehensive analysis of fine-grain beta diversity in continuous vegetation (Dengler et al. 2020).

The EDGG Field Workshop in Bulgaria in 2011 was only the third of this type of events and relatively small in terms of the number of participants and duration. Still, it yielded 15 nested-plot series (“EDGG Biodiversity Plots”) and additional 68 10-m² plots from two regions in NW Bulgaria. Prior to our study, hardly ever non-vascular plants had been included when studying the ecology of dry grasslands of the country – mainly because the respective expertise in the three taxonomic groups was spread among different people. Participants from abroad thus helped to ensure the comprehensive collection of the terricolous non-vascular plants, while the “critical” taxa among them later were sent to experts in different countries. An early paper from the Bulgarian Field Workshop on the phytosociology of the studied grasslands (Pedashenko et al., 2013) already led to interesting insights, including the first record of the lowland matgrass communities (Violion caninae) from the country. Taking into account not only vascular plants, but also bryophytes and lichens, supported the view that the meso-xeric sandy grasslands of the region (Armerio rumelici-Potentillion) are floristically and ecologically very similar to the East-Central European alliance Armerion elongatae and thus rather be placed in a common order (Trifolio arvensis-Festucetalia ovinae, class Koelerio-Corynephoretea) than in an endemic Balkan order (Astragalo-Potentilletalia, class Festuco-Brometea) as done before by phytosociologists from a regional perspective and disregarding the cryptogams.

Sandy dry grassland in the Koprivshtitsa region (Bulgaria), rich in cryptogams, such as Polytrichum piliferum (bryophyte) and Cladonia furcata (lichen). Photo credit: Jürgen Dengler.

Now, seven years later, we finally also completed the complementary study on biodiversity patterns and their drivers (Dembicz et al., 2020). As in similar studies before (e.g. Turtureanu et al., 2014; Kuzemko et al., 2016) we found striking differences between grain sizes and between taxa. Among others, we found that total species richness and richness of vascular plants were controlled mainly by pH (unimodal relationship) and inclination (positive), while the richness of bryophytes by rock cover (positively) and proportion of sand in the soil (also positive relationship). Elevation was the most important predictor of total species richness in 100 m2 plots, while heat load index was best predictor of total species richness in 1 m2 grain. In this regional study, we also looked into differences between life forms and functional groups of vascular plants. We found that richness of hemicryptophytes and graminoids was positively related to litter cover, while rock cover had a positive impact on the richness of phanerophytes and therophytes, but negatively influenced richness of hemicryptophytes and cryptophytes. Unlike previous similar studies, this time the spatial autocorrelation structure posed some challenges: we found that species richness within sampling sites was more similar and among sites more dissimilar than expected by the measured environmental parameters. All in all, we found some similarities, but also striking differences compared to previous regional studies of the same type. This calls for overarching studies of the whole Palaearctic biogeographic realm as they are now possible with the GrassPlot database, combining the data of all the EDGG Field Workshops as well as similar data of other researchers (Dengler et al. 2018).

Rocky dry grasslands in the Balkan Mts. Photo credit: Jürgen Dengler.

Apart from the scientific outcomes, the EDGG Field Workshops are also very special events for people interested in getting to know a flora very much in detail. Jointly, we study every part of the plot so carefully that we can be reasonably sure not to have overlooked a non-flowering grass, a seedling or a tiny acrocarpous moss. Doing this, we learn a lot from each other. A complete sampling of a 100 m² EDGG Biodiversity Plot with its two subseries in opposite corners (0.0001 to 10 m²), depending on the richness and structure of the vegetation, might take between one and six hours for a team of 4-6 experienced botanists, depending on the richness and structure of the vegetation. That way, we can ensure the high quality of the data in the GrassPlot database. However, studying a plot so carefully also gives one a deep insight into the organisation of the plant community and the fine details of discriminative characters between species. It can be almost meditative. Many colleagues from multiple countries really like this atmosphere and got kind of “addicted” to the Field Workshops and try to join again every year. Thus the Field Workshops grew in size, and sometimes there are now even two events per year.

After the cancellation of the planned 14th Field Workshop to Ukrainian steppes in early summer 2020 due to the Corona pandemic and its ad-hoc replacement by a small Field Workshop in alpine habitats of Switzerland in late summer 2020, we now hope that the situation allows to jointly study the Ukrainian steppes with an international team in May 2021. In case this report has risen your interest, you can join EDGG ( for free to ensure that you receive the invitation.

Returning from field sampling after a hot day in Bulgarian dry grasslands. Photo credit: Jürgen Dengler.