Alien plant species ‘invading’ world’s mountain regions

[NEW DELHI] Alien plant species are rapidly invading the world’s mountain slopes, a process facilitated by roads and human activity, according to new findings that covered 11 regions on five continents.

The global survey, published in Nature Ecology and Evolution, suggests that high-elevation ecosystems, so far spared by heavy invasions of non-native plants, are now under threat caused by warming climate and increasing human pressures, adding that the changing situation upland will have serious implications for local biodiversity and agricultural systems in the adjoining lowlands.

“Mountains provide many ecosystem services, such as water supply for lowland human settlements, and changes in mountainous ecosystems also have an influence on adjacent lowlands,” says Evelin Iseli, an author of the study and PhD student at the Institute of Integrative Biology, ETH Zurich. “Additionally, high elevation vegetation is species-rich, unique and contains many endemic species, and therefore has a high conservation value.”

“In times of global climate change, high-elevation ecosystems are faced with many challenges, such as increasing plant-plant competition due to other upward migrating native species. and the additional pressure of rapidly expanding non-native species can be a major threat to mountain flora”

Evelin Iseli, ETH Zurich

Invasive alien species — plants, animals and other organisms that stray outside their natural range — are a major cause of global biodiversity loss and species extinction, and a threat to food production, according to the International Union for Conservation of Nature.

“In times of global climate change, high-elevation ecosystems are faced with many challenges, such as increasing plant-plant competition due to other upward migrating native species. and the additional pressure of rapidly expanding non-native species can be a major threat to mountain flora,” Iseli tells SciDev.Net.

According to Iseli, because of man-made interference, non-native species are continuing to advance into high-elevation ecosystems. “These changes are so fast that we can observe them over less than a decade, highlighting the speed at which our vegetation is changing.”

Iseli and her teammates surveyed elevational gradients along mountain roads and adjacent seminatural vegetation in 11 mountain ranges across the globe including in the Australian Alps, the Swiss Alps, the Andes in Chile, the Montana-Yellowstone National Park in the US and Kashmir in India.

Non-native plant species were found expanding their upper elevation limits in 10 out of the 11 surveyed regions. The only region that did not show evidence of significant changes in the upper-range limits of non-native species was Chile.

On average, the number of non-native species increased by about 16 per cent per decade across regions with the direction and magnitude of upper-range limit shifts depending on elevation across all regions, the survey found.

“Roads provide favourable habitat and anthropogenic dispersal routes for many non-native plant species, and range expansions along roads are therefore expected to be more rapid than in undisturbed habitats,” the study said. “Non-native plant species spreading away from roads into the surrounding undisturbed vegetation have so far been limited at higher elevation but this might change with increasing anthropogenic disturbance and changing climate.”

According to Zafar Ahmad Reshi, dean of biological sciences at the University of Kashmir, the ecological and economic impact of invasive alien plant species could be more significant in biodiversity-rich areas like the Himalayas.

“The study is expected to raise concern among policy planners for better management of alien species with focus on low-cost, effective early detection and rapid response strategies,” says Reshi, an author of the study.

“Kashmir, being part of the Himalayan Biodiversity Hotspot, has prized endemic plants which face extinction on account of several anthropogenic factors,” he adds. “Species initially restricted to lower or middle elevations are spreading upwards significantly more than expected by chance alone — as the survey shows.”

Critically endangered plants in Kashmir, based on field explorations and herbarium records include: Saussurea costus, a thistle traditionally used for thyroid ailments; Gentiana kurroo, or Himalayan Gentian; Lilium polyphyllum, a species of lily known to cure stomach ailments; and Aconitum chasmanthum, or Gaping Monkshood, useful for treating boils and abscesses.

According to Reshi and other scientists who are a part of the Mountain Invasion Research Network, the role of roads as dispersal corridors is amplified due to increased vehicle traffic, often as a result of recreation and tourism. Roadside habitats also provide ideal spaces for non-native plants, which benefit from reduced competition, increased soil nutrients and water availability.

Reshi says that the spread of invasive species to higher elevations together with unprecedented changes in the climate could severely impact native biodiversity with implications for local populations that are dependent on this biodiversity for livelihood and survival.

“Roads can serve as conduits for plant invasions into new habitats and climate change can also promote invasions,” says Sumanta Bagchi, associate professor at Centre for Ecological Sciences at the Indian Institute of Science.

“The authors provided data on invasions along roads and relate it to climate change,” says Bagchi. “It is difficult to disentangle the two aspects — for translating these patterns into effective management, we will need more studies that focus on the underlying mechanisms and relate them to processes which operate at large spatial scales.”

“Addressing invasive species can be a challenge,” says Malvika Chaudhary, a weed biocontrol specialist who works with the ‘Action on Invasives’ programme for CABI, the parent organisation of SciDev.Net, in India. “However, in this era of digitalisation there are tools that support quick action that can subsequently be followed up with a contingency plan and policy interventions at the local level.”

This piece was produced by SciDev.Net’s Asia & Pacific desk.