Radiation generated by wireless networks that enable our ever increasing online communications has a detrimental effect on trees, a new study has claimed.

The research by a team from Wageningen University in the Netherlands found that trees planted close to a wireless, or wi-fi, router had bleeding bark and dying leaves.

The revelation will raise fears that wi-fi radiation may also be having an effect on the human body and supports parents who have campaigned to stop wireless routers being installed in schools, the Daily Mail reported.

However, findings of a number of studies carried out to measure radiation impact on human health have so far been inconclusive.

The Dutch city of Alphen aan den Rijn had ordered the new study after officials found unexplained abnormalities on trees.

As part of their research, the Wageningen University team took 20 ash trees and for three months exposed them to six sources of radiation.

Trees placed closest to the wi-fi source developed a "lead-like shine" on their leaves that was caused by the upper and lower epidermis -- the leaf's skin -- dying.

The researchers also discovered that wi-fi radiation could slow the growth of corn cobs.

In the Netherlands, 70 per cent of all trees in urban areas show the same symptoms, compared with 10 per cent five years ago, the study found. However, trees in densely forested areas are not affected.

The scientists behind the research, which has not yet been published, said that further studies were needed to confirm their findings.

The Dutch health agency issued a statement, stressing that "these are initial results and that they have not been confirmed in a repeat survey".

"There are no far-reaching conclusions from its results.

Based on the information now available it cannot be concluded that the wi-fi radio signals leads to damage to trees or other plants," it added.

Other scientists have expressed scepticism.

Marvin Ziskin, a professor of radiology and medical physics at Temple University in Philadelphia, said: "Stuff like this has been around a long time. There's nothing new about wi-fi emissions. Scientifically there's no evidence to support that these signals are a cause for concern."

In 2007, a BBC Panorama documentary found that radiation levels from wi-fi in one school was up to three times the level of mobile phone mast radiation. However, the readings were 600 times below government safety limits.

The new study is to be the subject of a conference in Holland in February.