Thorny issue - Invasive cactus takes root above the snowline

The residents of the Swiss 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.

- Alessio Perrone

Cactus species belonging to the genus Opuntia, or prickly pears, are proliferating in parts of Valais, posing a biodiversity threat as they encroach on nature reserves.

“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, Sion, where estimates suggest Opuntia plants make up 23-30% of the low vegetation cover. Their presence has also been reported in neighbouring Alpine regions, including Ticino and Grisons in Switzerland, and the Aosta valley and Valtellina in Italy.

“In some parts of Valais, we estimate that the cacti can occupy one-third of the available surface,” said Yann Triponez, a biologist who works in Valais’s nature protection service. He said Opuntia had been present in Valais at least since the late 18th century, when they had been imported from North America.