Even more dramatic was the rise in trees with severe treetop damage, up to 51 percent in 2005 from 9 percent in 1984.

"The situation for oaks is worrying," the ministry said in a statement. "At 51 percent, the level of severe treetop damage has hit a new record."

It said air pollution as well as parasites and unusual weather conditions had contributed to the damage.

The problem is a blow to a nation where politicians boast of "standing firm as a German oak" and where, even today, about one-third of the country is forested.

Thick woodland has been a key part of Germany's image from ancient times, when the tribal chieftain Hermann defeated the invading Roman legions in the murky Teutoburg forest to the 19th century Romantics and the fairy tales of the Brothers Grimm.

Environmental lobby groups said oaks had been especially hard hit because of their long life span of up to 1,000 years, which gives them more time to accumulate harmful substances.

"We have seen such a strong reduction of oaks in recent years," said Ruediger Rosenthal, spokesman for environmental lobby group BUND. "We cannot rule out any more that a tree species like the oak could disappear from our forests."

German environmental groups have campaigned against "Waldsterben" or "dying forests" since the 1980s, when stickers proclaiming "First the forest dies, then humans die" were a common sight.