Summary of risk assessments

Both Solidago species have been introduced and entered the risk assessment area in the past. A number of active pathways of introduction exist and entry into the environment is very likely with high confidence.

The species are already established in the risk assessment area and further establishment is very likely in both current and future climatic conditions. The species have a wide tolerance of habitats and abiotic parameters which promote their establishment. 

Solidago canadensis and S. gigantea exhibit vegetative and sexual reproduction in the risk assessment area. The high propagule pressure (seeds) facilitates the colonization of new (disturbed) habitats. Small root/rhizome fragments can form viable plants and are spreading clonally, forming monodominant stands. Based upon the species’ anemochory with tiny seeds, longdistance dispersal enables spread across landscapes to reach favourable and suitable habitats. Both Solidago species have spread across all climatically suitable biogeographical regions in Europe in about 175 years.

Both Solidago species have shown major impacts on biodiversity and ecosystem functioning and services through suppression of native species development and reducing species richness by forming dense monodominant stands.

Solidago canadensis and Solidago gigantea pose a high risk to the EU with high confidence. This overall risk conclusion score takes into account the major impact score already happening in several biogeographical regions, coupled 97 with a rapid spread. The high confidence score incorporates the high amount of evidence and references for the risk assessment area.