Wild pollinator communities are negatively affected by invasion of alien goldenrods in grassland landscapes

The increasing spread of invasive alien plants has changed biodiversity throughout the world. To date research in this area has focused on how invasive plant species affect pollinator behaviour, but there is a lack of data on the impact that alien plant species have on wild pollinator populations. Since their introduction in the 19th century, and rapid spread after the 1950s, alien goldenrods (Solidago canadensis, Solidago gigantea) have been among the most successful invasive plant species in Europe. We studied the effects of goldenrods on wild pollinator communities in SE Poland. The abundance, species richness and diversity of wild bees, hoverflies and butterflies were compared between wet meadows invaded by goldenrod (10 transects) and non-invaded controls (10 transects). Furthermore, we compared the plant diversity and average cover between the two groups of sites. Invasion of goldenrods had a very strong negative effect on wild pollinator diversity as well as abundance. Plant diversity and average cover were also negatively affected by goldenrod invasion. Wild pollinators were grouped according to their nesting and food specialization, but none were resistant to the invasion, indicating that introduced goldenrod may affect the entire wild pollinator community. Our study emphasises the urgent need to develop specific protection plans for wild pollinators in habitats threatened by foreign plants and we call for the introduction of programs to stop the invasion of goldenrod not only in Poland, but also on a continental scale.