PEOPLE AND farm animals are helping an invisible pollutant to change the types of plants that grow in Britain, according to the Natural Environment Research Council.

Nitrogen deposits are the cause of the problem.

The dung from farm animals produces vast quantities of ammonia, and the burning of fuels (coal, gas, petrol) causes massive emissions of nitrogen oxides into the atmosphere.

The result is that ammonia and nitrates are deposited back onto the land, acting as fertilisers and acidifying soils.

Nitrogen cascades through the environment like no other pollutant and at the right level is good, since plants depend on the use of nitrogenous fertilisers.

But this extra nitrogen is providing an environment for “takeover bids” on the land from more aggressive plant species.

The winners are the plants that can mop up nitrogen – grasses, brambles and nettles. They will move in on slower-growing plants that live in habitats where low levels of nitrogen are more usual – heather moorland will become grassland, for example.

Professor Alan Davison, co-ordinator of the Global Atmospheric Nitrogen Enrichment research programme, said: “What most people don‘t realise is that they are helping to change areas like the Pennines or the Lake District, which are considered to be unspoilt.”

“Their cars are small ‘fertiliser factories‘, so every time they start the engine nitrate is released and can be carried over long distances before falling on plants and soils.”

“The chicken and pork that we eat has played a part in contributing to the ammonia that is changing the biodiversity in our countryside. I wonder if farmers, including organic growers, understand that their land is receiving a significant amount of ‘free‘ fertiliser”, Prof Davison said.