Abstract
AbstractAimEuropean grassland communities are highly diverse, but patterns and drivers of their continental‐scale diversity remain elusive. This study analyses taxonomic and functional richness in European grasslands along continental‐scale temperature and precipitation gradients.LocationEurope.MethodsWe quantified functional and taxonomic richness of 55,748 vegetation plots. Six plant traits, related to resource acquisition and conservation, were analysed to describe plant community functional composition. Using a null‐model approach we derived functional richness effect sizes that indicate higher or lower diversity than expected given the taxonomic richness. We assessed the variation in absolute functional and taxonomic richness and in functional richness effect sizes along gradients of minimum temperature, temperature range, annual precipitation, and precipitation seasonality using a multiple general additive modelling approach.ResultsFunctional and taxonomic richness was high at intermediate minimum temperatures and wide temperature ranges. Functional and taxonomic richness was low in correspondence with low minimum temperatures or narrow temperature ranges. Functional richness increased and taxonomic richness decreased at higher minimum temperatures and wide annual temperature ranges. Both functional and taxonomic richness decreased with increasing precipitation seasonality and showed a small increase at intermediate annual precipitation. Overall, effect sizes of functional richness were small. However, effect sizes indicated trait divergence at extremely low minimum temperatures and at low annual precipitation with extreme precipitation seasonality.ConclusionsFunctional and taxonomic richness of European grassland communities vary considerably over temperature and precipitation gradients. Overall, they follow similar patterns over the climate gradients, except at high minimum temperatures and wide temperature ranges, where functional richness increases and taxonomic richness decreases. This contrasting pattern may trigger new ideas for studies that target specific hypotheses focused on community assembly processes. And though effect sizes were small, they indicate that it may be important to consider climate seasonality in plant diversity studies.
Highlights
Grasslands are among the most diverse ecosystems in Europe (Wilson et al, 2012; Dengler et al, 2020)
Environmental conditions act as an additional filter on plant communities, sorting those that fulfill local niche requirements constituted by physiological constraints (Leibold et al, 2004; Tingley et al, 2014)
Considering the variation of functional and taxonomic richness across precipitation gradients, we found a decrease in richness with increasing precipitation seasonality (Figure 2b, d; Appendix S9)
Summary
Grasslands are among the most diverse ecosystems in Europe (Wilson et al, 2012; Dengler et al, 2020). A third filter may be biotic interactions, representing a counter-gradient with competitive interspecific interactions being the main driver of plant community composition at low abiotic stress (the stress gradient hypothesis; Bertness & Callaway, 1994) While this competition may lead to exclusion of species and reduced trait variation (Grime, 2006; Mayfield & Levine, 2010; Kunstler et al, 2012), facilitative interactions have been suggested to dominate when abiotic stress is high (Bertness & Callaway, 1994; Brooker & Callaghan, 1998), leading to higher trait divergence and increased functional diversity (Valiente-Banuet & Verdú, 2007; McIntire & Fajardo, 2014). This expansion of the realized niche can be especially important for the diversity of plant communities in temperate regions (Scheiner & Rey-Benayas, 1994; Breitschwerdt et al, 2018)
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