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Human threat to grassland ecosystems

Posted June 3, 2015

A manmade pollutant is having a significant impact on our global environment according to a new study published in ‘Ecology’ this month (June 2015).


Human activity, such as burning forests and fossil fuels, increasing dependence on farm fertilizers and more livestock waste, has led to high levels of atmospheric nitrogen.

An international investigation, led by Dr Carly Stevens, found that grasslands – including prairies, alpine meadows and savannahs – grew more abundantly as atmospheric nitrogen increased.

Surprisingly, they also found atmospheric nitrogen had a bigger effect on grasslands growth than any other factor – including local climate and rainfall.

This increase in grassland growth has previously been linked with reduced species richness, which poses a threat to biodiversity.

Grasslands cover 40 percent of the earth’s surface storing 34 per cent of terrestrial carbon. Therefore any change to grassland growth patterns could have a significant impact on earth system processes.

This investigation was part of the global research co-operative Nutrient Network where researchers from across the world all conduct the same experiment and share their data to address a wide range of ecological questions.

Dr Carly Stevens said: “Atmospheric nitrogen, a pollutant which most people have probably never heard of, is actually having a great impact on our environment globally.

“Grassland habitats are important for conservation, atmospheric nitrogen is increasing productivity meaning that the habitat is being changed. Natural habitats are often adapted to low levels of nitrogen so adding it can lead to reductions in species richness and changes in species composition – which have demonstrated in a wide range of habitats in the past.”

Throughout the study, levels of local atmospheric nitrogen were compared with above-ground vegetation growth cut from two one metre strips at each site in peak growing time. The foliage was dried and weighed.

Researchers found the greater the amount of nitrogen in the atmosphere the more ‘above ground net primary production’ there was on grasslands; the more nitrogen in the atmosphere, the more vigorously the grasslands grew.

Scientists working on earth systems modelling and carbon cycle predictions now need to take more account of nitrogen deposition.

Source: Lancaster University

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