The first ash tree was planted along a 1.2-kilometre-long (0.75-mile-long) path that will link the Hainich National Park in eastern Germany to the Thueringia forest, said Angelika Zahrnt, the head of the environmental federation BUND.
It is 50 metres (164 feet) wide and will eventually comprise 20,000 trees and shrubs, she said.
Zahrnt added that the aim is to create a 20,000-kilometre network of paths across the country to allow wildcats to roam freely, increasing the chances of the European wildcat species to survive in Germany.
In recent years their numbers here have declined from dozens of thousands to between 3,000 and 5,000, and there are fears that the sharp-fanged predators could disappear from the country.
The cats are threatened by hunters and a lack of space