Local-scale increase masks landscape-scale loss of species richness in managed Pannonian grasslands

Context
While biodiversity decline is undebated on the global level, landscape-scale trends are poorly known and local assemblages even show stable species richness, accompanied by pronounced turn-over. The landscape-scale consequences of local-scale species turnover likely depend on whether species replacement is random or biased towards more frequent species in the metacommunity, but this potential bias is insufficiently studied.

Objectives
Here, we use grassland ecosystems of a Central European national park to simultaneously analyse time-series of local-scale species richness and landscape-scale species incidence to better understand how trends are linked at these two scales.

Methods
From 2013 to 2024 we sampled 120 plots per year and used regression methods to quantify changes in the number of species per assemblage, the incidence of species across assemblages and the relationship between initial incidence of species and incidence trends. To explore possible drivers of change, we further evaluated trends of community means of environmental indicator values.

Results
We found that local species richness has increased within the study period from 18 species per plot in 2013 to 21 species in 2024, while the overall number of species sampled per year stayed the same. In contrast, when looking at individual species trends we found an average decline of species’ incidence in the region. While a small pool of already common species became more frequent, the majority of species became rarer, leading to a pronounced homogenization of plant communities on the sampled sites. Indicator-value analysis showed that the species turnover was mainly influenced by desiccation of grasslands, significantly biassing incidence changes towards species that prefer drier conditions.

Conclusions
We conclude that in typical Central-European grassland ecosystems, anthropogenic drivers rather decrease landscape-scale than local-scale biodiversity, because they tend to homogenize environmental conditions. The resulting species turn-over can stabilize local species richness but depletes the metacommunity, thereby posing future risks to the regional biodiversity.