International travel and trade provide ample opportunity for plants to find their way into non-native soils. But some are quick to take root and influence both the economy and the environment.
It may have been back in 1492 that #link:https://en.wikipedia.org/wiki/Christopher_Columbus:Christopher Columbus# sailed upon America, but one could say his historic discovery served as the impetus for new research at the University of Konstanz. A team of scientists led by Wayne Dawson and Mark van Kleunen has been investigating how many plant species have successfully travelled – generally by human hand – and settled beyond their indigenous grounds.
These invasive plants, or Neophytes as recent incomers are collectively known, can have a significant impact on both their environment and the economic situation of their new homes.
Take the humble potato, for example, or tobacco or cocoa. Before Columbus embarked on his revelatory voyage, they were unheard of on the European side of the Atlantic. And that was just the start. As human travel became more commonplace, traders brought unknown species to every possible corner of the world.
"The start of the 20th century and the beginning of globalization of the economy caused a huge increase in the movement of people and of goods," Piero Genovesi, head of the #link:http://www.issg.org/:Invasive Species Specialist Group# at IUCN said. The numbers of species moved around the world increased much more rapidly then ever before."
Species are on the move, but how many?
Establishing just how many, is mammoth undertaking, but with the help of a gigantic database, the Konstanz researchers have identified more than 13,000 types of plant that have taken root in new places.
"We searched for published lists and compendia of naturalized alien plant species for geopolitical regions, digitized the lists, and standardized the taxonomy," Dawson said, adding that for some places – such as India and China - they had to create lists from scratch.
Given the sheer size of the overall plant kingdom, 13,000 species - which equates to four percent of the world's total plant - might seem like a small number to have travelled abroad. But that four percent, says Dawson "would be like the flora of a whole continent – Europe – becoming naturalized in other continents."
The number of all introduced species is higher, but as the scientists point out in their #link:http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14910.html:study#, not everything manages to thrive in its new habitat.
But in our increasingly interconnected world, the rate of newly introduced plants that do adapt to their new environments is set to increase.
Impact on humans and the environment
A species is described indigenous to a new area if it manages to develop a viable population without human assistance. The common sow thistle (Sonchus oleraceus) is one such plant. When it comes to the colonization of new species, it is one of the most successful species.
"It is present in almost half of the world’s regions covered by our database", Dawson says.
Another major example is the water hyacinth (Eichhornia crassipes), a plant with a delicate blossom, originally native to Latin America, and today available almost everywhere in the world.
"This is the species that has the highest economic costs at present in Europe", Genovesi said. A large part of that expenditure goes towards moving the plants from the waters where they have settled – waters in which they displace other plants that would naturally thrive there.
"In Africa it has a huge impact on local communities because it limits the possibility for families living on rivers to fish, it limits the possibility to travel along rivers and it decreases the availability of water", he continued.
What's more, the hyacinth also generates ideal conditions for mosquitoes, which implies diseases such as Malaria.
Evolution does its thing
Not every species has such a dramatic effect on its new environment as the water hyacinth, but each new arrival has some influence on its surroundings. Dawson says they have to, because they will be interacting with other, more established flora.
"If a naturalized plant species has traits that differ strongly from those of the native plants, it might change properties of the ecosystem invaded, such as the availability and cycling of soil nutrients. Some naturalized plants can act as important food sources for animals, such as pollinating insects, or fruit-eating vertebrates."
Determining whether an invasive species is a good or bad thing, the scientist says, depends on the relevant eco-system, on nature and on our individual perspective.
"Novel plants in novel environments means novel interactions, which sets the stage for evolution to continue in a way that would be different if species remained geographically separated on their own continents of origin," he concluded.
Billion-dollar losses and an open stage
Non-native plants can also damage buildings and infrastructures, and even increase the risk of flooding or fire. And that can be expensive.
Piero Genovesi was part of a group of scientists and economists that calculated the potential damage of invasive plants for the European Commission.
"We came up with an estimate of an overall loss of well above 13 billion euros per year in Europe," Genovesi said, adding that because the data was based on actual costs, it was an underestimate.
He believes if efforts are made to protect the environment, the knock-on effect will benefit the economy.
In January 2016, European legislation will attempt to address the issue of invasive plants by imposing a ban on the import of the most aggressive species.
"Countries will have an obligation to survey their territory, to protect from new invasions and immediately remove the very first species that may arrive in our territories", Genovesi said.