Increasing abundance of an invasive C-4 grass is associated with larger community changes away than at home

Aim We evaluated stands of the invasive grass, Sporobolus cryptandrus in its native North American range and its non-native European range, where it is a recent invader. Our aim was to reveal how the species' increasing abundance affects functional diversity and the ecosystem service-provisioning capacities of plant communities in both ranges. Location Sand grasslands in the Kiskunsag, Hungary and in Montana, USA. Methods All vascular plant species and their relative abundances were recorded in a stratified random manner in 1 m x 1 m plots in each range, using the following cover categories of Sporobolus as strata: 1%-25%, 26%-50%, 50%-75%, and 75%-100%. The functional characteristics of the plant communities in the two continents were compared. We performed comparisons of the communities both with and without including Sporobolus. Results Increasing Sporobolus cover resulted in a lower functional diversity and species richness, reduced average specific leaf area and increased the height of whole plant communities in both ranges but these effects were significantly stronger in the non-native stands. Sporobolus also negatively affected the cover of insect-pollinated plant species and the proportion of native perennials, switching the rest of the community from perennial-dominated to annual-dominated. In plant communities without Sporobolus, increasing Sporobolus cover led to a higher specific leaf area and seed mass in both ranges, but average height was decreasing along the Sporobolus abundance gradient in the native range, whereas it was increasing in the non-native range. Conclusions The spread of Sporobolus, away from its native range, leads to the impoverishment of host communities and compromises the biomass and floral resource-provisioning capacity of the vegetation to higher trophic levels. Tackling the spread of this new invader should therefore be a priority task.