The proliferation of Asian palms in Switzerland’s southern Ticino canton is threatening local species and posing increased fire risk, says a study.

In a report on the Chinese windmill palm (Trachycarpus fortunei) published on TuesdayExternal link, the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) recommends targeted measures to control its spread.

These ornamental, cold-resistant  trees have been planted in gardens over the past 50 years and spread to forests, particularly near residential areas. “Ticino's forests near residential areas now almost look tropical,” says WSL. “The palms have proliferated and in some places are displacing native plant species.”

The research team studied the flora and fauna at ten forest sites with high palm density or with no palms at all. WSL says the palm-rich sites did not contain fewer invertebrates, “but significantly fewer plant species”.

In addition, windmill palms weaken the protective function of forests against natural hazards, as their root system strengthens the soil only slightly, according to the study. And since many dry, dead leaves accumulate on the windmill palms, the researchers say they probably increase the risk of forest fires.

At present, these palm trees are restricted to forests at lower altitudes. However, WSL says they will also be able to colonise at higher altitudes if it gets warmer there with climate change.

The researchers conducted a nationwide survey on the public's perception of these trees and found that most people see them positively as a Ticino landmark. While bans would receive little support, WSL says, it is  recommending measures to limit their further spread, such as removing their flowers and fruits, removing stray plants, and planting alternative non-invasive palm species.

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