Habitat preferences of three Chorthippus species (Orthoptera: Acrididae) in the Chelmsford area
Sampling of vegetation characteristics
The height of the vegetation was recorded using the Boorman Drop Disc (Smith et al. 1993). The
disc is dropped from the top of a metre rale standing vertically and the height of the vegetation
where the disc settles is measured in millimetres. The disc weighs 200g and has a diameter of
300mm (Waring 1992). Four height measurements were obtained for each quadrat in the July 2000
survey. Percentage cover of the vegetation was estimated by eye for each plant species in every
quadrat in the July 2000 survey. The percentage cover values obtained for the plant species and the
bare earth at each site were converted to the Domin Scale which assigns cover value to a defined
category. Once each cover value was converted to the Domin scale, the median Domin value was
calculated for every plant species (and bare earth) at each site (Kent & Coker 1992). A high
median Domin value indicates an abundance of a particular plant species and the maximum value
that can be attained is 10.
Study sites
There were six sites surveyed during this study. Three of these study sites were located on the
predominantly agricultural Writtle College Estate (TL 670070) which is situated near Chelmsford
in Essex. The approximate size of the estate is 210 hectares, consisting of Sturgeon's Farm and
many horticultural and amenity areas. The other agricultural site is located at Highwood, 4km to
the south-west of Chelmsford. For comparison of these farmland habitats with more potentially
favourable areas, two acid grassland sites close to the College Estate were surveyed: Galleywood
Common and Mill Green Common.
Site descriptions
Agricultural sites (Writtle College Estate & Highwood)
Two set-aside grasslands were chosen as study sites: Writtle Set-aside (TL675069) and Highwood
Set-aside (TL625031). The former site has been an area of set-aside grassland since 1996 when it
was sown with Lolium species. The set-aside is cut once a year in August and the cuttings are left
in situ in accordance with the regulations outlined by Defra. Highwood Set-aside is an area of
grassland that was created in 1997 on Gorrell's Farm near Highwood. The field is mown once a
year in August and the cuttings left in situ.
Sturgeon's Track (TL663073) is a disused farm track that is not managed. The track was used as an
access route to a manure pile until 1995. It was frequently used by vehicles and the sward was
detrimentally affected, with much bare earth and short vegetation evident. However, since 1995
the grassland has remained unmanaged with very infrequent vehicular usage.
Long Meadow (TL674068) is a cattle-grazed pasture that is heavily grazed throughout the year.
This pasture is occasionally mown to regenerate the grass and to eradicate species such as Nettle
Urtica dioica and Creeping Thistle Cirsium arvense. High levels of fertiliser are applied regularly
and this is the most intensively managed of the four farmland survey sites and is therefore a 'control'
plot.
Essex Naturalist (New Series) 20 (2003)
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