Risk assessment and pre-alarm on invasive peculiarities of ornamental grasses to the urban greening routine

Abstract Two risk assessment protocols, the Weed Risk Assessment for Central Europe (WG-WRA) and the Australian Weed Risk Assessment (WRA), were adapted to evaluate the invasion risk of eighty-two ornamental grasses. Meanwhile, some particular characteristics of these ornamental grasses, like ornamental value, biological and ecological characteristics were highlighted and assessed for their potential risk by field observations and method of expert ranking. There was a positive correlation between scores derived from the two risk protocols, though WRA was considered to be more acceptable than WG-WRA according to the analysis of ornamental grasses. Anyhow, well-cultivated cultivars were less-efficiently predicted by the two risk protocols compared with the protospecies in the study, as well as some outliers with higher fecundity. In details, the risk classification differed: risk categorization using the WG-WRA protocol allocated high and moderate risk to 81.1% of 45 native grasses, yet only 22.2% of 37 alien species. Assessment using the WRA protocol scored 91.5% of the studied grasses to pose invasion risk following a diverse criterion, of which 97.3% were for native species and 86.7% for alien species. On details, ranked scores of biological and ecological characteristics of ornamental grasses highlighted herein were correlated with risk scores, although the significance of these relationships varied; while ornamental value had a weak relationship to the risk scores. In addition, some features peculiar to ornamental grasses relating to their invasive tendency are presented that most (72.0%) of the alien ornamental grasses exhibit perenniality, intentionally introduced from the Americas and Europe, and to a lesser extent from Asia, Africa, and Australia. In general, the ornamentals with high fecundity and adaptability presented a higher risk of invasion, while well-domesticated cultivars or hybrid species with high aesthetic scores yet relatively low levels of fecundity and adaptability, presenting a low invasion risk. Thus, special attention should be paid to the invasive characteristics of ornamental grasses to mitigate risks to agriculture and local ecosystems and also some amendments are needed to improve the risk assessment protocols at some certain case or even a larger scale during application in projects of urban greening and environmental restoration.