Habitat preferences of three Chorthippus species (Orthoptera: Acrididae) in the Chelmsford area
Acid grassland sites
Galleywood Common (TL 703028) is a relict of a once expansive heath and in 1993 it was designated
as a Local Nature Reserve by English Nature in recognition of its wildlife value (Chelmsford
Borough Council 1995). Many different habitats arc present on the common including grassland,
Ling Calluna vulgaris covered areas. Bracken Pleridium aquilinum stands and secondary woodland.
Much secondary woodland encroached onto the common during the 20th century and recently
efforts have been made to re-establish the former heathland. The survey site was a grassy area that
is being restored to lowland heath covered with C. vulgaris (Chelmsford Borough Council 1995).
Much young Birch Betula spp., Oak Quercus robur and other scrub has been removed, although
some still remains.
Mill Green Common (TL637013) forms part of the Writtle Forest ancient landscape and much of
the common is woodland with relict areas of heathland vegetation and acidic grassland present.
Mill Green Common is a registered common and has been designated a Wildlife Site (formerly
known as Site of Importance for Nature Conservation - SINC) by the Essex Wildlife Trust because
it possesses relict areas of heathland. There is evidence that the common was once grazed, but this
management practice ceased in the early 20th century and much secondary woodland has encroached
onto the common. The study site is a small area of acidic grassland with patches of heathland
vegetation. In the late 1970s, an attempt was made to create a cricket pitch in this grassy area and
much vegetation cover and soil was removed. This clearance inhibited scrub and P. aquilinum
encroachment, and may have caused the regeneration of a small area of C. vulgaris in the north-
east corner.
Statistical analysis
Kruskal-Wallis multiple comparison test (Heath 1995) was conducted using the total adult density
per m2for each of the three Chorthippus species to ascertain whether significant differences and
therefore habitat preferences occurred between the six study sites. Dunn's non-parametric procedure
(Gardiner 1997) was used to determine between which sites the significant differences in grasshopper
density occurred. Differences between mean sward heights at each site were tested using one-way-
Analysis of Variance (ANOVA) (Heath 1995). A Tukey test determined where the significant
differences occurred. All statistics were performed using SPSS statistical software (SPSS 1999).
Results
A total of 972 individuals of all three species were counted in the survey (Table 1). The most
common grasshopper species in the survey was C parallelus which comprised approximately 61 %
of all sightings. C. albomarginatus was also abundant. The least common species was C. brunneus.
Table 1: Proportion and number of sightings for the three
Chorthippus species for 2000 and 2001 combined
___________Species____________Proportion No. sightings
Chorthippus albomarginatus 0.33 316
Chorthippus brunneus 0.06 59
Chorthippus parallelus___________0.61_________597_______
_____________________Totals 1.00_________972_______
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Essex Naturalist (New Series) 20 (2003)