DOI: 10.5061/dryad.djh9w0w6g
title: Soil toxicity and species dominance rather than nutrient availability drive plant species richness in swamp forests of Central Europe

description: Aim: A resource-based conceptual model of plant diversity (RBCM) assumes
 direct relationships between resource supply and the diversity of a local
 plant assembly. However, the RBCM largely ignores variation imposed by
 soil toxicity due to climatic effects. Both soil-limiting resources and
 soil toxicity vary along climatic gradients but their net and interactive
 effects on plant species diversity remain unknown. We asked how climatic
 gradients shape resource availability, soil toxicity and dominance of
 herb-layer graminoids, and how these predictors control local species
 diversity of herbs and bryophytes. Location: Swamp forests,
 Central Europe Taxon: Vascular plants, bryophytes
 Methods: Alpha taxonomic diversity of vascular plants and
 bryophytes was counted for 101 vegetation plots sampled in temperate swamp
 forests distributed along an 800-km geographical gradient across the
 Continental, Alpine and Pannonian biogeographical regions. Path analysis
 (structural equation modelling) was used to quantify the direct and
 indirect effects of climatic variables (potential evapotranspiration;
 PET), limiting resources (soil N/P, Ca, C/N, proxies for light and water
 availability), and soil toxicity (Mn) on graminoid dominance and community
 diversity. Results: PET negatively influenced species richness of
 both groups analysed either directly or indirectly through its positive
 effect on the cover of graminoid species. Alpha diversity of herbs was
 additionally reduced by soil toxicity (Mn). Limiting resources correlated
 either with species dominance (canopy shading, soil Ca) or with PET (soil
 N/P ratio), but they did not control species richness pattern. Main
 Conclusions: Climate, soil toxicity and species dominance
 determined alpha diversity instead of the expected importance of soil
 limiting resources. These results are key to advancing the theoretical
 framework of the RBCM. Increased soil toxicity (Mn) in well-watered
 regions favours the dominance of plant competitors at the expense of less
 tolerant species. This implies a potential threat to wetland diversity
 under ongoing climate change.
description: # Soil toxicity and species dominance rather than nutrient availability
 drive plant species richness in swamp forests of Central Europe
 Vegetation and ecological
 data were retrieved from original field research of authors conducted in
 three biogeographical regions (Continental, Alpine and Pannonian) of
 Central Europe. We sampled 101 vegetation plots in stands of the *Alnus*
 swamp forests during the period of 2010–2019 using the traditional
 European phytosociological approach. A list of all vascular plants and
 ground-dwelling bryophytes was created in each plot. The dataset includes
 species richness for herb-layer plants (referred to as herbs) and
 bryophytes. Alpha diversity values are accompanied by a set of explanatory
 variables associated with the resource based conceptual model of plant
 diversity. We measured and/or calculated climatic (large-scale) variables
 and several site productivity variables (i.e. soil fertility measures,
 light and water conditions), environmental harshness (soil toxicity) and
 plant graminoid dominance. Summary statistics for all predictors
 (explanatory variables) and plant taxonomic diversity (dependent variable)
 in swamp forests are shown in Appendix S1 of the study. ## Description of
 the data and file structure The first column shows vegetation plots
 (numbered consecutively) recorded in swamp (alder-dominated) forests, and
 the row shows the names of the variables. Alpha taxonomic diversity
 (species richness) was counted for herb-layer species (herbs) and for
 ground-dwelling bryophytes. The species richness values are followed by
 the predictors used. These include climate (temperature [°C],
 precipitation [mm], aridity index, potential evapotranspiration [mm] and
 their seasonal values, latitude and elevation [m a.s.l.]), soil (pH,
 concentration of Ca [mg/kg], Mg [mg/kg], K [mg/kg], P [mg/kg], Mn [mg/kg],
 Fe [mg/kg], total C [%], total N [%], C/N, N/P, N/K ratios), proxies for
 light (canopy shading [%]) and water (waterlogging) conditions [binary
 variable], and plant graminoid dominance [%]. The column entitled
 "Biogeographical regions" shows the affiliation of each
 vegetation plot to the biogeographical region (Continental, Alpine,
 Pannonian). The last two columns give the geographical coordinates
 (latitude and longitude) of each plot. ## Sharing/Access information The
 geographical coordinates of each plot were used to derive climatic data.
 Temperature and precipitation (including their seasonal values) were
 retrieved from the CHELSA database. Aridity index and potential
 evapotranspiration (PET) were obtained from the Global Aridity and
 Potential Evapotranspiration Database ver. 3. Soil sampling and recording
 of water and light conditions (waterlogging/canopy shading) were performed
 in each plot. ## Code/Software All statistical analyses were conducted in
 R (R Core Team, 2021). Piecewise SEM models were calculated using the
 ‘piecewiseSEM’ package (ver. 2.1.2).