Rapid continental spread of a salt-tolerant plant along the European road network

R Fekete,D Schmidt,H Bak,Gy Haszonits,A Molnár V,O Vincze,K Süveges

doi:10.1007/s10530-021-02531-6

Abstract

The spread of alien species with the expansion of road networks and increasing traffic is a well-known phenomenon globally. Besides their corridor effects, road maintenance practices, such as the use of de-icing salts during winter facilitate the spread of halophyte (salt tolerant) species along roads. A good example is Plantago coronopus, a mainly coastal halophyte which has started spreading inland from the Atlantic and Mediterranean coastal habitats, recently reaching even Central European countries (e.g. Hungary). Here we studied the spread of this halophyte and tried to identify factors explaining its successful dispersion along roads, while also comparing native and non-native roadside occurrences with regard to altitude of the localities, size of roadside populations and frequency of roadside occurrences. We completed a comprehensive literature review and collected more than 200 reports of occurrence from roadsides spanning a total of 38 years. During systematic sampling the frequency of the species along roads was significantly higher in the Mediterranean (native area), than along Hungarian (non-native area) roads, however the average number of individuals at the sampling localities were very similar, and no significant difference could be detected. Using a germination experiment, we demonstrate that although the species is able to germinate even at high salt concentrations, salt is not required for germination. Indeed salt significantly decreases germination probability of the seeds. The successful spread of the species could most likely be explained by its remarkably high seed production, or some special characteristics (e.g. seed dimorphism) and its ability to adapt to a wide range of environmental conditions. Considering the recent and rapid eastward spread of P. coronopus, occurrences in other countries where it has not been reported yet can be predicted in coming years.

Highlights

Due to globalization, road networks are growing rapidly all over the world, Europe harbours one of the longest road networks, where the length of paved roads was almost 5 million kms by the end of 2017, out-rivaling even the United States and China (European Road Federation 2020)
Between 1980 and 2000 only 15 P. coronopus occurrences were reported from roadsides, while this number increased to 50 between 2000 and 2010, and 153 occurrences were reported between
While publication rates increased rapidly during the last four decades, which might have an influence on the latter records, the increasing speed of dispersion of P. coronopus is indicated by documented spread of the species by several earlier works as well as floristic records in multiple regions. 82 documented occurrences reported information about the size of the population

Summary

Introduction

Road networks are growing rapidly all over the world, Europe harbours one of the longest road networks, where the length of paved roads was almost 5 million kms by the end of 2017, out-rivaling even the United States and China (European Road Federation 2020). The construction and management of roads is usually associated with several types of disturbances, such as frequent mowing, use of herbicides, trampling by humans or vehicles, introduction of a range of pollutants or propagules of alien species embedded within the modified soils used for the construction (Sera 2008; van der Ree et al 2015). Another management practice involves the spraying of deicing salts (most frequently NaCl) during winter which has become a common practice, during the last few decades (Houska 2007). Halophytes are plant species, which are able to survive and reproduce in environments where salt concentrations are at least 200 mM NaCl (Flowers and Colmer 2008)

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Conclusion