Functional traits predict resident plant response to Reynoutria japonica invasion in riparian and fallow communities in southern Poland.

Marcin W Woch,Małgorzata Stanek,Szymon Zubek,Anna M Stefanowicz,Paweł Kapusta,David Gorchov

doi:10.1093/aobpla/plab035

Abstract

Reynoutria japonica is one of the most harmful invasive species in the world, dramatically reducing the diversity of resident vegetation. To mitigate the impact of R. japonica on ecosystems and properly manage affected areas, understanding the mechanisms behind this plant’s invasive success is imperative. This study aimed to comprehensively analyse plant communities invaded by R. japonica, taking into account species traits, habitat conditions and seasonal variability, and to determine the ecological profile of species that withstand the invader’s pressure. The study was performed in fallow and riparian areas in southern Poland. Pairs of adjacent plots were established at 25 sites with no obvious signs of recent human disturbance. One plot contained R. japonica, and the other contained only resident vegetation. For each plot, botanical data were collected and soil physicochemical properties were determined. Twelve sites were surveyed four times, in two springs and two summers, to capture seasonal variability. The presence of R. japonica was strongly associated with reduced resident plant species diversity and/or abundance. In addition to the ability to quickly grow and form a dense canopy that shades the ground, the success of the invader likely resulted from the production of large amounts of hard-to-decompose litter. The indirect impact of R. japonica by controlling the availability of nutrients in the soil might also play a role. A few species coexisted with R. japonica. They can be classified into three groups: (i) spring ephemerals – geophytic forbs with a mixed life history strategy, (ii) lianas with a competitive strategy and (iii) hemicryptophytic forbs with a competitive strategy. Species from the first two groups likely avoided competition for light by temporal or spatial niche separation (they grew earlier than or above the invasive plant), whereas the high competitive abilities of species from the third group likely enabled them to survive in R. japonica patches.

Highlights

Japanese knotweed (Reynoutria japonica) is one of the world’s most problematic invasive species (Lowe et al 2000; EPPO 2020)
The aims of our study were to: (i) characterize differences in the resident plant community structure resulting from the invasion by comparing R. japonica patches and adjacent vegetation patches, (ii) link the occurrence of resident plants with soil properties and the season and (iii) identify functional traits that enable resident plants to coexist with R. japonica
According to PERMANOVA, the R. japonica plots did not differ from the resident vegetation plots in terms of soil physicochemical properties

Summary

Introduction

Japanese knotweed (Reynoutria japonica) is one of the world’s most problematic invasive species (Lowe et al 2000; EPPO 2020). This species, which is native to Asia, was introduced into Europe in the 19th century. This is an ecologically plastic, clonal, fastgrowing, herbaceous, perennial geophyte that dramatically reduces the occurrence of native species, causing biotic. Received: 5 November 2020; Editorial decision: 19 May 2021; Accepted: 2 June 2021. Its monodominant stands are sparse to widespread, and can be found from lowlands to the submontane areas of temperate climate zones in Europe (EPPO 2020)

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