"Long before it's in the papers"
January 27, 2015


Invasive plants use our shoes, tires as transport, scientists say

March 4, 2014
Courtesy of Umeå university
and World Science staff

They hitch­hike with us un­der the soles of our shoes and mud­dy car tires. Harsh, cold cli­mates don’t seem to stop al­ien plants from con­quer­ing moun­tain ar­eas, and glob­al warm­ing is mak­ing the prob­lem worse, ac­cord­ing to a new study in Nor­way.

Sci­en­tists are ask­ing hik­ers to clean their shoes and oth­er equip­ment be­fore trips.

“Alien plants of­ten gain ad­van­tages in their new en­vi­ron­ment be­cause they lack nat­u­ral en­e­mies,” said ecol­o­gist Ann Mil­bau of the Cli­mate Im­pacts Re­search Cen­tre in Abisko, Swe­den.

In a study pub­lished in the jour­nal PLoS One here, Mil­bau, with Jo­nas Lem­brechts of the Uni­vers­ity of Ant­werp, Bel­gium in­ves­t­i­gated how plants nor­mally grow­ing at low­er ground can spread high­er up.

Moun­tains have so far been seen as the last nat­u­ral ports of ref­uge, where al­ien spe­cies should have trou­ble es­tab­lish­ing them­selves due to the harsh cli­mate and tough com­pe­ti­tion from na­tive plants adapted to sur­vive cold, wind and short sum­mers.

But al­ien plants are no long­er rare above the Arc­tic Cir­cle, the re­search­ers said. “Aliens start their con­quest in the low­lands and fol­low hu­man roads and walk­ing tracks in­to the moun­tains,” Lem­brechts said.

In low­er ter­rain, the study found, the new spe­cies stick to the road­sides. But fur­ther up the moun­tain, the na­tive vegeta­t­ion seems more vul­ner­a­ble and the in­vaders swarm out­ward. “Most like­ly, these al­ien low­land spe­cies are be­com­ing in­creas­ingly suc­cess­ful in al­pine ter­rain due to the warm­er weath­er we have ex­pe­ri­enced in the past dec­ades,” said Mil­bau.

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They hitchhike with us under the soles of our shoes and muddy car tires. Harsh, cold climates don’t seem to stop alien plants from conquering mountain areas, and global warming is making the problem worse, according to a new study in Norway. Scientists are asking hikers to clean their shoes and other equipment before trips. “Alien plants often gain advantages in their new environment because they lack natural enemies,” said ecologist Ann Milbau, assistant professor at the research station Climate Impacts Research Centre in Abisko, Sweden. In a study published in the journal PLoS One Milbau, with Jonas Lembrechts of the University of Antwerp, Belgium investigated how plants normally growing at lower ground can spread at higher altitudes in subarctic mountain areas in Norway. Mountains have so far been seen as the last natural ports of refuge, where alien species should have trouble establishing themselves due to the harsh climate and tough competition from native plants adapted to survive cold, wind and short summers. But alien plants are no longer rare above the Arctic Circle, the researchers said. “Aliens start their conquest in the lowlands and follow human roads and walking tracks into the mountains,” Lembrechts said. In lower terrain, the study found, the new species stick to the roadsides. But further up the mountain, the native vegetation seems more vulnerable and the invaders swarm outward. “Most likely, these alien lowland species are becoming increasingly successful in alpine terrain due to the warmer weather we have experienced in the past decades,” added Milbau.