Global Warming To Aid Bracken Invasion

Abstract from Global Change Biology
15th April 1996

All over upland Britain there is a battle going on between the heather and the vigorous and invasive bracken. At the moment, the bracken is winning - there are estimated to be 300,000 hectares (three quarters of a million acres) dominated by it.

The rich diversity of heather moors, with a profusion of insects and birds such as the economically vital Red Grouse, contrasts strikingly with bracken areas. Here there are very few insects or birds and the plant itself is a carcinogen often eaten by cattle.

In a recent experiment on the hillside in Upper Teesdale, scientists from Sheffield University tried to find out what will happen if the current rate of global warming continues. They placed small polythene tents over bracken and areas of bracken and heather to mimic the raise in temperature, and applied light doses of fertiliser to reproduce other effects.

Ben Werkman, one of the team reporting results in Global Change Biology, said the effects were startling. The bracken responded by growing for longer, growing taller and becoming more dense. Global warming will surely cause further losses to heather moorland in many areas where it is not controlled by spring frosts.

Ornithologists are very worried by these predictions because heather moorland is a rich and characteristic habitat of upland Britain. Very common small birds, like the Meadow Pipit and Skylark, shun the bracken areas because of the lack of their insect food. These birds in turn are food for the rare falcon, the Merlin.

Humphrey Crick, of the British Trust for Ornithology, has recently worked on Golden Plover breeding biology. His results clearly showed that heather moorland was the best habitat for this declining wader. Encroachment by bracken would be disastrous for moorland breeding waders like the Golden Plover, Curlew and Lapwing. Bracken, once fully established, is impossible to eliminate without very time-consuming and expensive procedures. Typically, a series of mechanical cuts of the fronds, and chemical spraying, are needed over a number of years.

The effect on Red Grouse may be particularly important because many upland areas are as good as they are for a wide variety of wildlife simply because they are preserved for shooting. If the game were to disappear, and the vegetation becomes impossible for sheep grazing, there will inevitably be moves to plant more conifers, and the rich moorland communities will be lost.

Chris Mead