Due to global warming, Swiss mountainside cacti have replaced snow.
Due to global warming, cacti have taken the place of snow on the Swiss mountainsides. Invasive species that are spreading throughout Valais are encroaching on natural reserves and threatening biodiversity.
The occupants of the Swiss canton of Valais are accustomed to seeing their mountainsides shrouded with snow in winter and edelweiss blossoms in summer. However, as global warming intensifies, an invasive species is increasingly colonizing the slopes: cacti.
Authorities say that prickly pears, or species of cactus in the genus Opuntia, are spreading throughout parts of Valais, encroaching on natural reserves, and threatening biodiversity.
“A lover of dry and hot climates, this invasive and non-native plant is not welcome in the perimeter of prairies and dry pastures of national importance,” the municipality of Fully in the Rhone valley said in a press release announcing the uprooting campaign in late 2022.
In the hills surrounding Sion, the capital of Valais, Opuntia species and related cacti have also spread. According to estimates, Opuntia plants now account for 23-30% of the low vegetation cover. Additionally, their presence has been reported in Italy’s Aosta Valley and Valtellina, as well as Switzerland’s Ticino and Grisons.
“In some parts of Valais, we estimate that the cacti can occupy one-third of the available surface,” says Yann Triponez, a biologist who works in the canton of Valais’ nature protection service. He says Opuntia have been present in Valais at least since the late 18th century, when it was imported from North America.
However, authorities believe that the ideal conditions for their spread may be a warmer climate in the Alps that allows for longer periods of vegetation and decreasing snow cover.
“These species bear -10C or -15C without any problem,” says Peter Oliver Baumgartner, a retired geology professor with a longstanding side interest in botany who has been commissioned by the canton to study and write a report on the plants. “But they want to be in a dry place and don’t like snow cover.”
Even in the Alps, snow is becoming less common at lower elevations. Meteo Swiss claims that since 1970, the number of snow days in Switzerland below 800 meters of elevation has decreased by half. According to a recent study that was published in the journal Nature Climate Change, the amount of snow that covers the Alps is “unprecedented in the last six centuries” and lasts for about a month less than historical averages.
The range’s temperatures have been rising twice as quickly as the global average, and Switzerland’s average temperatures are already 2.4 degrees Celsius higher than the averages from 1871 to 1900. “If you look at climate change reports,” Baumgartner says, “the curves for Switzerland are almost as steep as for the Arctic.”
Nine species have spread to sunny slopes with a southerly orientation below 700 meters, where they compete with endemic and occasionally threatened species. “Valais is one of the biodiversity hotspots in Switzerland,” says Triponez. “We have about 3,000 species of plants in Switzerland, and some 2,200 are in Valais.”
He says authorities are worried by the cacti’s spread to natural reserves and protected areas. “When you have these cacti, nothing else grows,” says Triponez. “Each pad covers the soil and prevents other plants from growing through.”
According to Baumgartner, only four of the nine Opuntia species found in Valais pose a threat to the local ecosystems. This is especially true in areas with acidic or neutral soils, which make up one third of the south-facing slopes in the valley.
Because Baumgartner’s report, which has not yet been published, is the most recent attempt to estimate the plants’ presence in the region, quantitative data about their spread are incomplete. However, according to Baumgartner, there is ample evidence of their expansion in numerous locations he has visited.
In Fully, the uprooting campaign will resume in the coming weeks, and Triponez claims that authorities have also launched an awareness campaign to raise awareness of the threat among tourists and residents, who frequently plant the cacti.
It won’t be easy to stop Opuntia from growing in numbers. The plants reproduce quickly, recover quickly from uprooting, even after being cut down, stepped on by hikers, or left dry for months.
In Sion, eradication efforts were unsuccessful a decade ago. When the species were uprooted last year in Fully, the plants were scattered throughout a forest because authorities feared that the humidity and shade would cause them to rot and become compost. However, the pads at the top of the heap appeared to be flourishing when Baumgartner visited. At the same time, the cacti are growing back in most of the places where they were uprooted, which raises questions among biologists like Baumgartner about whether or not the cacti can ever be eradicated.
“We can restrict them,” he says. “But I don’t think we can get rid of them.”
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