Curiosities There are 17 times as many tree species in Swiss cities as in the forest

There are more than 1,300 tree species in Switzerland's cities. In contrast, only 76 different types of trees grow in the surrounding forests, according to a new study by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).

This makes the cities a gateway for forest pests, the WSL announced on Monday. According to the study, introduced pests have more hosts in the city than in the forest due to the large variety of trees in cities.

"Consequently, urban environments are an ideal place for monitoring measures that enable early detection and control of the introduction of invasive species," the researchers wrote in the study, which was published in the journal "Landscape and Urban Planning".

"Comparison was worthwhile"

For their study, the WSL researchers compared the tree species composition in 26 Swiss cities with that in surrounding forests. To do this, they searched the so-called tree registers from all over Switzerland. A tree register is a directory in which municipalities record individual trees.

"This made the comparison of urban and surrounding forest trees worthwhile. Cities are generally considered to be poor in diversity and forests rich", forest conservation expert Benno Augustinus was quoted as saying in the press release.

However, the high species diversity in cities must be put into perspective, wrote the WSL. This is because a few species, such as maples and lime trees, usually dominate in terms of numbers.

SDA