Competitiveness of the Exotic Silphium perfoliatum against the Native Urtica dioica: A Field Experiment

Abstract

Silphium perfoliatum (cup plant) is native to North America and is increasingly used as a bioenergy crop in Germany. Spontaneous occurrences of this species have already been detected in several European countries. To assess the possible risk to biodiversity by spreading of S. perfoliatum, we investigated the competitiveness of this species against the native and highly competitive Urtica dioica over four years in a field experiment in Bayreuth (Germany). S. perfoliatum grew well among U. dioica, although its biomass was strongly reduced by surrounding U. dioica. Projection area, plant height, and reproductive potential were less or similarly reduced by surrounding U. dioica as by the intraspecific competition. Moreover, S. perfoliatum significantly suppressed the growth of the competitive U. dioica. A settlement and establishment of S. perfoliatum in the native flora of Central Europe and a suppression of uncompetitive plant species are therefore conceivable.

Dispersal and persistence of cup plant seeds (Silphium perfoliatum): do they contribute to potential invasiveness?

“…Due to the high value for nature conservation of riparian fringes and floodplains (Finck et al 2017), the possible dispersal of cup plant seeds by water courses and the associated colonisation of these habitats should be considered critically from an invasion biology perspective. Because of the high competitiveness of the cup plant -especially under moist conditions -a suppression of native species is conceivable there, and therefore a risk for biodiversity is possible (Ende et al 2023). In some regions of Europe, dominance stocks of cup plant are already recorded (Brennenstuhl 2010;Zykova and Shaulo 2019;Vladimirov 2021;Shynder et al 2022).…”

“…Until now, an invasive behaviour was not reported in Germany. However, several studies suppose a certain invasive potential, because of its spread, its preference for moist habitats, which are often valuable for nature conservation, and its high competitiveness (Ende et al 2021(Ende et al , 2023Ende and Lauerer 2022). Another important trait that promotes the spread and thus the invasive behaviour of a plant species is the effective dispersal of the diaspores (Coutts et al 2011).…”