The team surveyed vegetation at ten sites along the two rivers, which are small tributaries of the Tanew River within the Vistula basin. The sites were chosen to represent the dominant land-use contexts of the valleys, ranging from allotment gardens and residential areas to hydrotechnical infrastructure, tree plantations, semi-natural meadows and agricultural land. Between spring 2023 and spring 2025, the researchers recorded the composition and cover of herbaceous vegetation in 150 phytosociological plots, each measuring two by two metres. The plots were arranged along transects running perpendicular to the river channel, capturing the ecological gradient from the water’s edge to the valley margin. Tree and shrub cover were assessed at the site level, since these layers often extended beyond individual plot boundaries.

To characterise the ecological conditions of each site, the researchers calculated Ellenberg indicator values, a widely used European system in which the plant species present at a location act as living gauges of light, temperature, moisture, soil reaction and nitrogen availability. Because plants integrate environmental conditions over time, these values provide a practical, field-based proxy for habitat quality without the need for extensive instrumentation. The team also computed classic diversity metrics, the Shannon-Wiener index and Simpson’s index, and constructed a vegetation-based Index of Biotic Integrity, a composite score that combines diversity, the share of alien and invasive taxa, indicator species and Ellenberg values for moisture and nitrogen into a single measure of ecological condition.

The most compelling result came from a species-level analysis. Using 217 unique species as observational units, the researchers applied logistic regression to ask whether a species’ invasion status could be predicted from its fixed, literature-based Ellenberg indicator classes. The answer was emphatic. With each step up the nitrogen indicator scale, the odds of a species being classified as invasive increased roughly 4.3-fold. With each step up the temperature scale, the odds increased approximately 6.3-fold. Soil reaction showed only a marginal, negative association, while light and moisture played no independent role in the final model. The model discriminated well between invasive and non-invasive species, achieving an area under the receiver operating characteristic curve of 0.818.

In plain terms, the invasive flora of these Polish river valleys is dominated by eutrophic and thermophilous taxa: plants that favour nutrient-rich soils and warmer conditions. This makes intuitive sense in a landscape where agricultural runoff, urbanisation and recurrent disturbance continually enrich riparian soils and open up bare ground. Fast-growing, disturbance-tolerant invaders such as giant goldenrod, Solidago gigantea, which was the most frequently recorded invasive species in the study, appearing at four sites across both agricultural and built-up contexts, are precisely the kinds of plants equipped to exploit such conditions. Other recorded invaders included Canadian horseweed, barnyard grass, Jerusalem artichoke, bigleaf lupine and Oregon grape, alongside woody aliens such as box elder, black locust, black cherry and staghorn sumac.

The composition of invasive assemblages differed noticeably between the two rivers. An ordination analysis based on non-metric multidimensional scaling showed that sites along the Biala Lada clustered tightly, indicating a relatively homogeneous set of invasive species dominated by herbaceous ruderal taxa. Sites along the Czarna Lada were more widely dispersed, with woodland-associated sites harbouring woody aliens such as black locust, black cherry and staghorn sumac, as well as the tall perennial Canadian goldenrod. Infrastructure-related sites were associated with box elder, while agricultural sites occupied isolated positions in the ordination. These patterns suggest that different groups of invaders exploit different habitat conditions within the same riparian system, with herbaceous invaders favouring disturbed, nutrient-enriched ground and woody aliens more often establishing near built-up and engineered environments.

The study also documented how invasion relates to community structure. Sites with greater occurrence of invasive alien species tended to show reduced evenness, increased dominance of ruderal taxa and stronger floristic homogenisation, a process in which a small set of widespread, disturbance-tolerant species replaces locally characteristic assemblages. This echoes a long-standing idea in ecology, first articulated by Charles Elton in 1958, that structurally complex and diverse communities resist invasion more effectively than simplified ones. Interestingly, the relationship between diversity and dominance was not straightforward: sites with similar Shannon diversity values sometimes differed markedly in Simpson’s index, indicating that low diversity can arise either from strong dominance by a few species or from species-poor but relatively even assemblages. Combining complementary diversity metrics, the authors note, is therefore essential when interpreting homogenisation.

A principal component analysis integrating Ellenberg values, vegetation structure and channel morphology revealed that the first two axes together explained nearly seventy percent of the variance among sites. The first axis contrasted wider, tree-shaded channels with steeper, more open sites dominated by herbaceous vegetation, while the second separated nutrient-rich, base-rich sites from those with greater shrub cover. A permutation test confirmed that this structure was unlikely to be an artefact of averaging indicator values, a known pitfall in vegetation science. Meanwhile, the Index of Biotic Integrity, scored on a scale of zero to thirty, ranged from seventeen to twenty-eight across the ten sites, with higher values at sites with structurally complex, native-dominated vegetation and lower values where alien taxa and simplified structure prevailed.

The authors are careful about the limits of their conclusions. Because several land-use categories were represented by only one or two sites, land-use effects could not be formally separated from site-specific conditions, and the study is framed as an exploratory case study rather than a generalisable test. Notably, transect-level models did not detect a significant relationship between the proportional cover of invasive species and weighted mean Ellenberg values, meaning that while the invasive species pool has a distinct ecological profile, the amount of invader cover at a given site could not be statistically linked to the habitat conditions measured there. The findings on diversity and invasion are therefore presented as local descriptive patterns rather than evidence of causal land-use effects.

Even so, the practical implications are considerable. Riparian corridors function simultaneously as reservoirs of native biodiversity and as dispersal pathways for alien plants, and identifying which species are most likely to invade, and under which conditions, is a key step in targeting management. The authors suggest that Ellenberg indicator values and the vegetation-based Index of Biotic Integrity can serve as complementary screening tools, helping to flag sites where vegetation structure and composition indicate reduced ecological integrity. Such approaches may complement existing European policy frameworks, including EU Regulation 1143/2014 on invasive alien species and the Water Framework Directive’s biological assessment tradition. As climate warming and nutrient enrichment continue to reshape European landscapes, the combination of nutrient-loving and warmth-seeking traits among invaders is a warning worth heeding: the riverbanks most altered by human activity may be the ones most easily conquered.

Subject of Research: Ecological characteristics of invasive alien plant species in riparian ecosystems of two lowland rivers in eastern Poland

Article Title: Invasive alien plants in riparian ecosystems: a study from two lowland rivers in Eastern Poland

Article References: Invasive alien plants in riparian ecosystems: a study from two lowland rivers in Eastern Poland. (n.d.). https://doi.org/10.1007/s11356-026-38279-6

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38279-6

Keywords: invasive alien species, riparian ecosystems, Ellenberg indicator values, Index of Biotic Integrity, floristic diversity, biotic homogenisation, eutrophication, lowland rivers, logistic regression, vegetation ecology, Poland, land use