Cacti on Swiss Mountainsides

In Switzerland, the residents of the canton of Valais are used to seeing their mountainsides covered with snow in winter and edelweiss flowers in summer. But as global heating intensifies, they are increasingly finding an invasive species colonising the slopes: cacti. 

 

Authorities say cactus species belonging to the genus Opuntia or prickly pears, are proliferating in parts of Valais, encroaching on natural reserves and posing a biodiversity threat. 

 

 

 

 

 

 

 

 

 

 

 

 

 

“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 an uprooting campaign in late 2022. 

 

Opuntia species and similar cacti have also proliferated in some of the hills around the capital of Valais, in Sion, where estimates suggest Opuntia plants now make up 23-30% of the low vegetation cover. Their presence has also been reported in neighboring Alpine regions, including Ticino and Grisons in Switzerland, and the Aosta valley and Valtellina in Italy. 

 

Yann Triponez, a biologist who works in the canton of Valais’ nature protection service explains that Opuntia have been present in Valais at least since the late 18th century, when it was imported from North America. 

 

But authorities believe that a warmer climate in the Alps, allowing for longer vegetation periods, and the diminishing snow cover might be creating the ideal conditions for them to spread. 

 

Already, snow is becoming rarer at lower altitudes, even in the Alps. According to Meteo Swiss, the number of snow days under 800 metres of altitude in Switzerland has halved since 1970. A recent study published in Nature Climate Change said snow covers the Alps for about a month less than historical averages and called the situation “unprecedented in the last six centuries”. 

 

Nine species have spread on sunny, south-facing slopes below 700 metres of altitude, where they compete with endemic and sometimes 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”. 

 

Preventing Opuntia from proliferating will not be an easy task. The plants reproduce easily, growing back even when felled, stepped on by hikers or left dry for months, and recover quickly after they are uprooted.