Invasive cacti are taking over mountain slopes in the Swiss canton of Valais. According to authorities, in some places they already make up to 30% of the low vegetation cover.

Biologists said cacti have been present locally since at least the late 19th century, when they were introduced from North America. But until recently, their spread was held back by cold winter weather.

But as the snow has retreated in the mountains, some species of cacti have spread across sunny slopes up to 700 m above sea level. They now threaten the local ecosystem as they displace any other vegetation, including rare species on the brink of extinction.

A local researcher added that the cacti are rare survivors, making them very difficult to control. They are able to reproduce even when they are chopped down, pulled out of the ground or deprived of moisture for months at a time.