Germany's forests are in a worrying state and nearly one third of all trees are showing signs of damage. The situation among oak trees is of particular concern, with half in poor condition, the study carried out by the agriculture ministry in 2005 found.
The main causes of the damage were air pollution from motor vehicles and contamination of the soil from agriculture.
"The state of health of forests remains a source of concern," Peter Paziorek -- a state secretary in the agriculture ministry -- said Tuesday.
He called for stricter air pollution measures to be introduced and an increase in the use of environmentally friendly fuel.
The report by the agriculture ministry said 29 percent of trees showed signs of damage or disease in 2005, a slight improvement on the 31 percent in 2004.
However, the state of oak trees had worsened dramatically, while 20 percent of fir trees were in a poor condition compared with 17 percent in 2004.
The German farmers' federation (DBV) blamed the Europe-wide heatwave in 2003 and the high ozone levels it triggered for much of the damage.
Environmental group NABU said the report was alarming.
"Such a picture of damage being painted repeatedly and so often proves the clear threat to the very existence of forests," the group said.
It called for an end to mass livestock rearing which it said contributed to soil pollution from chemicals.
