Invasive plant species in the Swedish flora: developing criteria and definitions, and assessing the invasiveness of individual taxa

Abstract

In a north European context, identifying invasive species is far from trivial because the vegetation has been influenced by human activities for thousands of years. New species have immigrated continuously since the end of the last glaciation, both spontaneously and through direct or indirect help by man. Still, newly immigrated species may be problematic in a nature conservation context and may harm biodiversity, and cause changes in ecosystem services. In this study, all 721 presently established vascular plant and bryophyte taxa known to have been introduced to, or to have immigrated to, Sweden since the year 1700 are assessed for their invasive potential. The assessment is based on six components considered relevant for their invasiveness: 1) ability to compete in natural vegetation, 2) ability to form dense populations, 3) realized dispersal ability, 4) gene flow to native relatives, 5) time since immigration and 6) distance to their native range. Although the relative importance of these components is context dependent, a compound general index of invasive concern is proposed and calculated for all taxa. The index of invasive concern is validated by comparing it to assessments by a Bayesian Belief Network in which the influences of the same six components are assigned by expert opinions. In addition, rough estimates of the present‐day abundance of each taxon in Sweden are presented. The origin, biology and possible impact of the 150 taxa with the highest index values are discussed. Based on the index of invasive concern, Campylopus introflexus, Epilobium adenocaulon, E. ciliatum, Rosa rugosa, Lamiastrum galeobdolon subsp. argentatum, Orthodontium lineare, Solidago canadensis, Calystegia sepium subsp. spectabilis, Rubus armeniacus and Prunus serotina are identified as the ten most problematic alien vascular plant and bryophyte taxa in Sweden.

Climate warming and land‐use changes drive broad‐scale floristic changes in Southern Sweden

“…To become established and resident members of the flora, newly immigrated species need to spread and increase. Since only those recent immigrants that have successfully established were included in our analyses, their average increase thus partly follows from their definition (Tyler, Karlsson, Milberg, Sahlin, & Sundberg, ). However, the continued increase in the newcomers also means that there is an on‐going change, or turnover, of the flora in addition to that explained by the environmentally related factors in the analyses.…”

The last step towards a full revision of Hieracium sect. Vulgata in Sweden

“…Although many of these species have been found persisting in or close to the former parks well over a century after their presumed introduction, and many new sites have been detected since the works of Hylander (Tyler unpubl. ), only 3–5 of them have proven able to spread by their own means in their introduced range and may be considered invasive (Tyler et al ). Unfortunately, at least in Sweden, the cultural and botanical values of these parks have not been generally recognized and many sites have recently been destroyed by new buidlings or changed management regimes, while other sites are abandoned and suffer from gradual overgrowth.…”

Hieracium sylvularum (Asteraceae) in the Mordovia State Nature Reserve: invasive plant or historical heritage of the flora?

“…It is considered as locally established in Sweden on several localities, as a good competitor, forming stands and having a frequent dispersal. Due to this fact it was assessed as invasive with a moderate impact on the native habitats and vegetation (Tyler et al, 2015). In Central Russia it was also assessed as an established and potentially invasive species (Mayorov et al, 2013), but not a pure invasive plant (Vinogradova et al, 2010).…”