REMOVAL OF PONIES BENEFITS GRASSHOPPERS IN DUNWICH FOREST

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Suffolk Natural History, Vol. 50 REMOVAL OF PONIES BENEFITS GRASSHOPPERS IN DUNWICH FOREST TIM GARDINER

Concern was expressed in a recent paper about the damaging effects of Dartmoor pony grazing on grasshoppers (Orthoptera: Acrididae) of heathland in Dunwich Forest (Gardiner 2012). The grazing appeared to be detrimental to the herbaceous understorey leaving little suitable habitat for the Nationally Scarce woodland grasshopper Omocestus rufipes, which requires diversity in grassland structure (e.g. tall and short vegetation). Dartmoor ponies were grazing on the north side of the road which runs through Dunwich Forest. Unfortunately, they did not leave much taller vegetation (apart from bracken Pteridium aquilinum) that would be suitable habitat for the woodland grasshopper, which was absent from this closely cropped sward (<10 cm in height). The negative effect of pony overgrazing upon the orthopteran assemblages of the New Forest (Tubbs, 1986; Pinchen, 2000; Denton, 2006) and Mardyke River Valley (Gardiner & Haines, 2008) is well documented. Denton (2006) outlined the importance of exclosures, from which grazing ponies were largely excluded, for the conservation of Orthoptera in the New Forest. For example, both the woodland grasshopper and wood cricket Nemobius sylvestris were found in exclosures; the varied and taller vegetation structure created in the absence of excessive grazing being particularly important (Denton, 2006). In the Mardyke Valley, only four species were recorded in pony grazed floodplain, compared to seven in ungrazed pastures (Gardiner & Haines, 2008). In Dartmoor pony grazed woodland and heathland at Dunwich Forest only two species were observed by the author (field Chorthippus brunneus and mottled Myrmeleotettix maculatus grasshoppers) in 2011 (Gardiner, 2013). However, in ungrazed heathland with scattered birch trees, six species were observed including the mottled, woodland, and stripe-winged Stenobothrus lineatus grasshoppers. After concerns were raised about the damaging effects of pony grazing in Dunwich Forest (Gardiner, 2012), Suffolk Wildlife Trust (led by Dorothy Casey) removed all Dartmoor ponies in March 2013 to relieve some of the grazing pressure on grasshoppers at this site for a year or two. During a survey in July 2014 in the previously overgrazed heathland in Dunwich Forest north of the road (grid reference: TM454722), six species of grasshopper were recorded (only two were seen in 2011 due to the uniformly short sward created by pony grazing) (Table 1). After removal of the ponies, a variable sward height of 5–100 cm has developed, suitable for short (e.g. mottled grasshopper) and long sward (e.g. common green grasshopper Omocestus viridulus) specialists (see Plate 5 for 2014 sward). This compared with only four species in ungrazed heathland on the south side of the road outside of the Forest where there was also less variation in sward height (5–60 cm) and considerable bracken encroachment. Where pony grazing has been restricted, a patchy sward with heather Calluna vulgaris, purple moor-grass Molinia caerulea, sheep’s sorrel Rumex acetosella and bare earth has developed providing a mosaic of micro-habitats for grasshoppers. The

Trans. Suffolk Nat. Soc. 50 (2014)


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REMOVAL OF PONIES BENEFITS GRASSHOPPERS IN DUNWICH FOREST by Suffolk Naturalists' Society - Issuu