Rapid upwards spread of non-native plants in mountains

Ecologists from the global Mountain Invasion Research Network (MIREN) – including members of the RCAAE (John Morgan, Keith McDougall, James Shannon) – found that the number of non-native plant species in mountainous regions around the world has increased over the last 5-10 years, and that already established species are rapidly spreading to higher elevations.

Compared to lowland ecosystems, mountains have been less invaded by non-native plant species. However, with climate warming and increasing human pressure at high elevations, this situation is changing. While upward movements of native species in mountains are well recognized and relatively well documented, long-term studies on non-native species in mountainous regions are rare. To fill the gap, a global network of researchers has been monitoring non-native species along mountain roads since 2007. Now, a first assessment of the ongoing spread of non-native plants in mountains across continents has been published in Nature Ecology & Evolution.

The long-term study reveals increasing numbers of non-native plant species in high mountains.

Overall, the study found a significant increase in non-native species richness (approximately 16%) in mountains over the last 10 years. Considering that ecological processes such as the establishment of new species and range expansion often take place over long periods of time, the increase in the number of detected non-native species within a decade is surprising and alarming.  However, as the trends greatly varied among the eleven regions included in the study (New South Wales and Victoria [Australia], Central and South Chile, Hawaii, India, Montana and Oregon [USA], Norway, Switzerland and Tenerife), the overall increase in species richness could only be detected by pooling observations from multiple regions, highlighting the importance of globally replicated studies to detect temporal trends within short time periods.

The upward movement of non-native species was mostly at lower and mid elevations.

The invasion of mountain ecosystems is not only marked by an increasing diversity of non-native species, but also by an upward movement of species already present when the survey started. Moving to higher altitudes and latitudes to follow their preferred temperature is a well-known escape strategy for plants in times of global climate warming. Indeed, the analysis of the upper range limit changes within the study period revealed range expansions occurring in 10 out of the 11 surveyed regions. However, as non-native species are often initially introduced in the lowlands, from where they find their way into the mountains, an upward spread can be expected even without the effect of climate warming. This corresponds with the finding that in some of the surveyed regions, change was only detectable for species occurring in the lower or middle part of the surveyed elevational gradient. Nonetheless, climate change might enhance the upward spread of already established species, emphasizing the need to monitor their movements and prevent any negative consequences in high elevation ecosystems.

More Information:

Nature Ecology & Evolution: https://www.nature.com/articles/s41559-022-01979-6

Project Website Mountain Invasion Research Network (MIREN): https://www.mountaininvasions.org/