LEVELS of airborne bracken spores, which have been linked to cancer, are to be measured in a major study by scientists based in Scotland.

Dr Eric Caulton, director of the Scottish Centre for Pollen Studies (SCPS) at Napier University, in Edinburgh, said it would be the first time such a research project had been carried out on a UK-wide basis.

Bracken cover has more than doubled since the 1940s, perhaps because of climate change, leading to a reduction in heather cover and threatening species which rely on that habitat. Environmentalists are concerned that bracken control programmes appear to be at an ''all-time low''.

A Borders seminar on the subject was organised last week by the Scottish Environment Protection Agency (Sepa) and similar discussions are due to take place on Mull next month.

A Southern Uplands Bracken Working Group was formed following last week's talks to bring together farmers, landowners, scientists and conservationists and develop a ''coherent policy''. It is hoped further initiatives will now be launched around the country.

Aerobiologist Dr Caulton, who has carried out a 10-year study of bracken levels in Edinburgh, said the findings of SCPS work to date, which are due to be published, show that levels of bracken spores in the capital have not reached a dangerous level.

However, he added that walkers, climbers, farmers and forestry workers may be exposed to much higher levels in the countryside, particularly when bracken usually spores between August and October.

Other studies have identified bracken spores as a cause of cancer of the respiratory tract in laboratory rats. It is also been established that bracken can have a ''drastic'' effect on grazing livestock, Dr Caulton added.

He said: ''More people should be aware of the potential dangers, particularly when it comes to rambling and hiking in certain areas. It is a nasty plant with high toxicity and definite carcinogenic properties.

''The levels we are finding are sufficiently low so as not to pose a hazard to health in an urban situation. However, the problems are in the countryside and that is what I am anxious to tap into now.''

Dr Caulton will contact the 12 official pollen monitoring stations around the UK, including another Scottish site at Invergowrie, to request access to their data and samples from 1997 his chosen year of study. He will also request information from a further 40 individuals and organisations who monitor aerial spores on a less formal basis.

He said that would allow him to draw up a comprehensive picture of bracken levels around the country.

Dr Caulton said: ''More and varied urban airborne spore counts would give a better picture of the degree of health hazard posed within the UK.

''We plan to extend our investigations into airborne bracken spore concentrations in both urban and rural situations over the next few years.

''Nothing on this scale has been done before in Britain. Bracken has really developed in the last six years and although it was planned to do a UK-wide survey, nobody has actually done it yet.''

Bracken is classed as a cosmopolitan weed, which means is grows around the world. Sepa estimates that a lack of bracken control has allowed it to expand at a rate of up to 3% a year in this country.

A spokesman for the environment watchdog said the spread of bracken was eating into pasture land and killing heather and some rare ferns, such moonwort. The loss of habitat for vulnerable ground-nesting birds, such as grouse, is also causing concern. However, bracken can also provide habitats for endangered species, such as some butterfly.

The spokesman added that a further problem was that bracken harbours cattle ticks and scab mites, which can carry the potentially fatal Lyme disease.

He said farmers were given one-off payments to clear bracken but on-going treatment was required to prevent it re-growing.