Spread of common species results in local-scale floristic homogenization in grassland of Switzerland

Abstract

Aim We assess changes in plant species richness and changes in species dissimilarity at local scale in Swiss grassland between the time periods 2001-2004 and 2006-2009. Further, we provide an ecological interpretation of the observed taxonomic homogenization of vascular plants. Location Switzerland. Methods Changes in species richness and changes in Simpson dissimilarity index of vascular plants in grassland (meadows and pastures) were examined. The analyses were based on species lists recorded on 339 10-m 2 sample plots from a systematic sample covering the entire Switzerland. Each sample plot had been surveyed once in 2001-2004 and once in 2006-2009 with 5 years between the first and the second survey. Changes in species dissimilarity were interpreted by comparing the relative contribution of several indicator species groups.Results Mean species richness of vascular plants in grassland increased during the study period. In contrast, species dissimilarity of plants decreased, suggesting local-scale floristic homogenization of grassland in Switzerland. It was mostly because of the spread of common species, namely the species that are tolerant to high nutrient levels, the species of low conservation value and the species adapted to moderate temperature levels that led to taxonomic homogenization. Target species for conservation did only marginally affect taxonomic homogenization. In contrast to the predictions from studies of taxonomic homogenization on larger scales, the taxonomic homogenization of grassland at local scale was not explained by the spread of neophytic species.Main conclusions The biotic diversity of grassland in Switzerland changed considerably between 2001-2004 and 2006-2009. The observed taxonomic homogenization was merely because of the spread of common species. Localscale changes in land use regimes implemented by agri-environmental schemes and other conservation efforts on parts of the entire grassland area were, apparently, not enough to prevent the total grassland from recent taxonomic homogenization.

Concordance and discordance between taxonomic and functional homogenization: responses of soil mite assemblages to forest conversion

“…Furthermore, across a range of terrestrial and aquatic organisms, Baiser et al (2012) found that the biotic homogenization at a broad scale (regional to continental) was more attributable to the changes in species richness than the reductions in spatial turnover. Our result based on the local scale contrasts with this broad-scale finding, likely resulting from differences in the factors reshuffling communities at different spatial scales (Bühler and Roth 2011;Karp et al 2012;Trentanovi et al 2013). At larger scales, the processes behind the observed changes in species richness may be explained by biogeographical theories such as the interplay between immigration and extinction (Baiser et al 2012).…”

“…The resultant nestedness component is also referred to as "richness difference," which represents how differences in species richness that are not due to species turnover contribute to patterns of the overall β-diversity (Legendre 2014). Notably, several recent studies have shown that biotic homogenization sometimes occurs despite no net change in local species richness (α-diversity) (Bühler and Roth 2011;McCune and Vellend 2013;Rodrigues et al 2013), which is in contrast to the well-documented patterns of biotic homogenization associated with a net loss of biodiversity resulting from the response of sensitive specialist species to habitat modifications (Clavel et al 2011). Considering such variable effects of local species richness on the spatial variations of communities among localities, separating the effects of α-diversity from the overall β-diversity will be an important step to further help understand the causes and consequences of biotic homogenization.…”

Long-term hay meadow management maintains the target community despite local-scale species turnover

“…Examples in this study could be Scorzoneroides autumnalis, Trifolium pratense and Prunella vulgaris, which are common grassland 'generalists'. It is likely that a longer time period is needed to assess such changes particularly in grasslands where most of the species are perennials (Bühler and Roth 2011). In addition to the indication of greater homogenization at the regional level, the significant decrease in site species richness suggests that within-site diversity has also declined.…”

“…Bühler and Roth (2011) found that taxonomic homogenization was a result of an increase in more common species. Examples in this study could be Scorzoneroides autumnalis, Trifolium pratense and Prunella vulgaris, which are common grassland 'generalists'.…”

“…In previous re-visitation studies the focus has often been the substantial change in grassland community composition in regions where more intensive farming practices have replaced low input management (Prince et al 2012;Wesche et al 2012;Krause and Culmsee 2013). Some studies of vegetation in meadows which have a long history of extensive management have investigated particular aspects of change such as the homogenization of meadow vegetation (Bühler and Roth 2011) and the loss of rare meadow species (Bradshaw 2009). Only a small number of long-term studies have concentrated on meadows managed for both agricultural and conservation objectives.…”