Until now, mountain regions have been largely spared from biological invasions. But a new monitoring study shows that alien plants are spreading rapidly to higher altitudes along transport routes worldwide.
Neophytes use roadsides as gateways of entryHumans, whether deliberately or unintentionally, often introduce alien plants in lowlands, then plants spread from their starting point to higher elevations, particularly along roads, which is why the researchers focused on traffic routes. Along roads, neophytes have a particularly easy time because propagules are readily dispersed by people and because the natural vegetation is disturbed; competition with native species that have adapted to the prevailing climate is, therefore, weakened.
In intact mountain habitats further from roads, on the other hand, biological invaders have a tougher time, as Iseli points out. "If the original vegetation is intact, it takes much longer for neophytes to establish themselves and spread."
Data from around the worldThe data on which the study is based comprises of almost 15,000 observations of 616 non-native plant species from 651 study plots and are collected worldwide using the same procedure. The researchers record the alien species in T-shaped study plots, i.e., a 50-meter-long strip along mountain roads and a perpendicular strip of 100-meters (see diagram). The study areas are distributed at regular intervals along multiple mountain roads in each region.
The vegetation surveys were carried out in southern and central Chile, two regions of Australia, Tenerife, Switzerland, two regions of western USA, Hawaii, Kashmir, and Norway.
This study is conducted by the Mountain Invasion Research Network (MIREN), which was founded in 2005. Its goal is to scientifically study "redistributions" of both alien and native species in mountain areas and to provide a basis for neophyte management. Jake Alexander, senior scientist in the Plant Ecology group at ETH Zurich, was co-chair of MIREN from 2015 - 2019.
"The current study makes it clear that we need to expand biodiversity monitoring programs worldwide and take action to avert any negative consequences for mountain ecosystems and their flora and fauna," Alexander emphasizes. "The time to act is now because we can literally see our mountain environments changing."