Bracken and ticks on grouse moors in the North of England.

Abstract

Bracken encroachment onto heather-dominant moorland has resulted in a significant reduction in the amount of heather available to stock and game. In the North Yorkshire Moors, it has been estimated¹ that nearly a fifth of the moorland is dominated by bracken and the weed is currently spreading at the rate of 1.0% per annum. The direct replacement of heather by bracken results in the loss of winter food for sheep² and a reduction in grouse-producing ground³.  Other disadvantages of bracken include its toxic⁴ and carcinogenic⁵ properties as well as harbouring parasites harmful to grouse and sheep⁶.

The sheep tick, Ixodes ricinus, is an ectoparasite of both sheep and grouse and transmits a number of harmful diseases including louping-ill, tick-borne fever and tick pyaemia. Ticks and their associated diseases result in financial loss for both the hill farmer⁷ and grouse-shooting interests⁸. Control of the tick usually involves the treatment of sheep with an ixodicide to reduce the incidence of tick infestation and, when necessary, the administration of drugs to combat disease, The owner or tenant of a grouse moor is unable to control directly the tick infestation on the grouse but may implement effective control through the removal of habitat beneficial to the over-winter survival of ticks. In studies on ticks, Milne⁹ has found an association between rough grazing and ticks, with a positive correlation between mat thickness and tick population density. The ticks require a humid habitat in which to survive, and this is provided by the thick mat layer associated with rough moorland grasses and bracken.

This paper examines the association between bracken and ticks and reports some findings from a pilot experiment to test the idea that the removal of bracken could result in a decrease in mat thickness and consequently a decrease in tick abundance.