Short Communication Journal of Orthoptera Research 2020, 29(2): 127-131 Initial impact of a soil disturbance technique (disc harrowing) on Orthoptera in a grass heath in Breckland, UK Tim GARDINER! 1 Environment Agency, Iceni House, Cobham Road, Ipswich, IP3 9JD, Suffolk, UK. Corresponding author: Tim Gardiner (tim.gardiner@ environment-agency.gov.uk) Academic editor: Maria-Marta Cigliano | Received 9 March 2020 | Accepted 15 May 2020 | Published 14 September 2020 http://zoobank.org/D5743264-A38C-4EA 1-B353-99985B297689 Citation: Gardiner T (2020) Initial impact of a soil disturbance technique (disc harrowing) on Orthoptera in a grass heath in Breckland, UK. Journal of Orthoptera Research 29(2): 127-131. https://doi.org/10.3897/jor.29.51900 Abstract Ona Breckland grass heath in eastern England, soil disturbance methods such as disc harrowing employed to benefit endangered plants such as tower mustard, Arabis glabra, could also create exposed ground for localized in- sects, specifically the mottled grasshopper, Myrmeleotettix maculatus. Orthop- tera of disc-harrowed strips on a grass heath at Santon Warren in Norfolk, UK, were monitored in 2018 and 2019. Data analysis focused on two target species, field grasshopper, Chorthippus brunneus, and M. maculatus, which are likely to respond positively to the creation of early successional habitat. Of the two species, M. maculatus was found in significantly high abundance on the disc-harrowed strips, whereas C. brunneus was not. The species richness of Orthoptera did not appear affected by harrowing, although three species at this location (lesser marsh grasshopper, Chorthippus albomarginatus, long- winged conehead, Conocephalus fuscus, and Roesel’s bush-cricket, Roseliana roeselii) need taller vegetation than was present on the disc-harrowed strips. Keywords Acrididae, bare earth, bush-crickets, conservation, grasshoppers, heath- land, Tettigoniidae Introduction Breckland is a biodiversity hotspot in the UK; 25,500 species were recorded in a recent audit led by the University of East Anglia (Dolman et al. 2012). Over 2,000 of these species were of national conservation concern. The flora includes over 120 nationally rare and threatened plant species with many dependent on the remain- ing dry grassland and heathland that survived afforestation in the 20" century (Robertson and Hawkes 2017). The grasshopper fau- na (Orthoptera: Acrididae) of Breckland is relatively impoverished in comparison, with only six native species (55% of the national total of 11 species) (Richmond 2001, Gardiner 2018a). Despite the dearth of species, grasshoppers are an important component of grassland ecosystems, consuming up to 8% of net primary pro- duction (Kohler et al. 1987). Grasshoppers are a crucial link in food chains as prey for spiders and avian predators in particular (Latchininsky et al. 2011). Densities of grasshoppers often exceed 3 adults/m? in dry acid grassland and heathland, indicating that they can be an abundant food source (Gardiner et al. 2002). Be- cause of this, grasshoppers have been listed as a key invertebrate group in the Breckland Natural Area profile. Different grasshopper species have contrasting microclimatic preferences (humidity and temperature) that drive the diversity of assemblages (Gardiner et al. 2002, Gardiner and Dover 2008). Short grassland and heathland swards may be unfavorable for some grasshoppers due to high microclimatic temperatures (>44°C) at 10 cm above the soil surface (Gardiner and Hassall 2009), which can lead to shade-seeking behavior and vigorous escape responses in several grasshopper species. The optimum air temperature for the development of grasshoppers in the UK is thought to be 35-40°C (Willott 1997), although at high eleva- tions in the Alps (>2000 m above sea level), temperatures never reach these levels, limiting the reproductive potential of the com- mon green grasshopper, Omocestus viridulus (Berner et al. 2004). Responses to microclimatic temperatures differ between spe- cies. For example, the mottled grasshopper, Myrmeleotettix macu- latus, is a short sward specialist, and its small size may be an ad- aptation for the high temperatures it experiences (Willott 1997). Contrastingly, O. viridulus, a tall grass species in the UK (Marshall and Haes 1988), is a large insect that can overheat in short, hot grasslands/heathlands and, therefore, avoids those habitats (Gar- diner 2010). Tall grassland may also have higher humidity that is more favorable for this grasshopper (Berner et al. 2004). Warren and Bittner (2009) highlighted that disturbance caused by military activities can help conserve populations of the blue- winged grasshopper, Oedipoda caerulescens, which needs plentiful (30-50%) bare earth in its habitat. Many insects can be classified as either disturbance-dependent or disturbance-averse, depending on the level of disturbance of the vegetation cover they need to persist. Bare earth provides sites where grasshoppers can bask to warm up (exposed soil is often much hotter than surrounding veg- etation; Key 2000) and where adult females of species such as the field grasshopper, Chorthippus brunneus, which lay their egg pods in exposed soil (Choudhuri 1958), can deposit their egg load after mating. Bare earth is the earliest stage of succession and is often lacking in grasslands due to a dearth of soil disturbance caused by an absence of grazing livestock. Grasslands without management can become tall and rank and have little exposed soil (Grayson and Hassall 1985, Ausden and Treweek 1995, Gardiner 2018b). JOURNAL OF ORTHOPTERA RESEARCH 2020, 29(2) 128 Myrmeleotettix maculatus was the scarcest species recorded in a recent survey of Breckland (Gardiner 2013, 2018a), being ob- served at only two sites (East Wretham Heath and Thetford Warren Lodge). In the Breckland survey, there seemed to be an absence of the open ground for this disturbance-dependent grasshopper. At Thetford Warren Lodge, it was abundant on lichen heath, a seem- ingly scarce habitat at the other survey sites. It is the aim of this short communication to determine the initial impact of the soil disturbance technique of disc harrowing on Orthoptera of a grass heath in Breckland, UK, focusing on two disturbance-dependent species: C. brunneus and M. maculatus. Methods Site.—The study site on Santon Warren (52°27'43.2468'N, 0°40'23.8224"E) in Breckland, Suffolk, UK, was a grass heath composed of fine-leaved grasses (Agrostis and Festuca spp.) with rare annual plants (tower mustard, Arabis glabra) dependent on soil disturbance for their persistence. The grass and lichen heath developed on a sandy soil (with flint) and underlying chalk bed- rock. Formerly, rabbit (Oryctolagus cuniculus) grazing checked grass growth and scrub development, but since the myxomatosis out- break in the 1960s, this influence has declined. Therefore, other methods of creating bare ground were required to encourage the proliferation of rare plants. Soil disturbance technique.—Two strips of grass heath (300 m length) with little exposed bare ground (<10%) were randomly selected for soil disturbance with agricultural discs attached to the back of a tractor. The primary aim of disc harrowing in this area was to promote the abundance of the plant A. glabra (Neal Armour- Chelu personal communication). The vertical discs harrowed the surface and upper layers of the soil (Robertson and Hawkes 2017) to a width of 2.5 m and a depth between 8-18 cm. Disc harrowing has been regularly employed in Breckland in recent years to con- serve rare plant populations and promote invertebrate abundance (Robertson and Hawkes 2017). The two strips were disc-harrowed in February 2018 with adjacent grass heath left untouched (Fig. 1). Vegetation was allowed to naturally regenerate on the strips. Orthoptera sampling methods.—In each disc-harrowed strip and in an adjacent control strip, a 1-m wide x 300-m long transect (the same length for the disc-harrowed strip and the control) was es- tablished, closely following the methodology of Gardiner et al. (2005) and Gardiner and Hill (2006). The disc-harrowed and control strips were parallel to each other but at least 10 m apart to reduce the risk of double counting. Two target species, C. brun- neus and the more localized M. maculatus, were the focus of adult monitoring, although individuals of all species were also recorded to determine assemblage composition and species richness. The former grasshopper is an abundant species in Breckland, while M. maculatus is localized and probably declining in response to the lack of soil disturbance on grass heath (Gardiner 2018a). The two target species should be model insects for studying the re- sponses to disc harrowing as both require bare earth during their life cycle for basking and oviposition (Marshall and Haes 1988). It is acknowledged that the narrow nature of the disc-harrowed strips meant that frequent movements of grasshoppers between bare earth and surrounding unmanaged heath were unavoidable. Therefore, the surveys were a snapshot of strip usage, indicating their favorability for basking or oviposition, rather than as a self- contained breeding habitat. T. GARDINER Fig. 1. Disc-harrowed strips in May 2018, three months after disc harrowing, showing partial revegetation and variation in exposed substrate. Each transect was walked at a slow, strolling pace (2 km/hr) from May-July of 2018 and 2019 (5 surveys in each year, 10 in to- tal). Nymphs flushed from a 1-m wide band in front of the observ- er were recorded along the center of the 2.5 m harrowed strip and in the control. As it is difficult to distinguish between species in the early instars, nymphs of both species were lumped together for re- cording purposes. The surveys were undertaken in vegetation suf- ficiently short (<50 cm) to minimize the possibility of overlooking nymphs in tall grass (Gardiner et al. 2005). With practice, it was relatively easy to ascertain the species of adults without capture (Gardiner and Hill 2006). In addition to nymphs and adults of the two grasshopper species, other orthopteran species were counted on transects to provide an estimate of assemblage abundance and species richness. The weather conditions on survey days were fa- vorable for insect activity, being largely sunny and warm (>17°C). Statistical analysis. —The counts for each transect were standardized to 0.1 ha to give a clearer indication of usage of strips and control. To correct for non-normality, the data for both grasshopper spe- cies and the species richness were square-root transformed (Heath 1995). The mean density/0.1 ha of nymphs, adults of C. brunneus and M. maculatus, and overall species richness were compared be- tween the disc-harrowed strips and control in both years using a 2-way ANOVA. Results A total of 811 nymphs (70% of total recorded) were observed on the disc-harrowed strips in both years combined, compared to 353 on the control transects. Adults of both species were numer- ous (both years combined, C. brunneus: 729 individuals, M. macu- JOURNAL OF ORTHOPTERA RESEARCH 2020, 29(2) T. GARDINER latus: 559). The disturbance-dependent species M. maculatus was almost exclusively recorded on the disc-harrowed transects (552 adults observed, 99% of total) compared to the control (just 7 adults). Adults of C. brunneus were more evenly distributed (434, or 60%, on disc-harrowed transects and 295 on control). Densities of nymphs (Fig. 2) were not significantly different between disc-harrowed strips and controls (F = 6.77, P = 0.06) or year (F = 2.18, P = 0.21) with no interaction between factors (F = 0.01, P = 0.93). Densities of C. brunneus adults were not sig- nificantly different between disc-harrowed strips and controls (F = 0.98, P = 0.38) or year (F = 1.14, P = 0.35) with no interac- tion between treatment and year (F = 0.21, P = 0.67). In contrast to C. brunneus, densities of M. maculatus adults were significantly different between disc-harrowed strips and controls (F = 299.58, P = 0.0001) but not between years (F = 3.35, P = 0.14) and with no interaction between factors (F = 0, P = 1). Overall, five species of Orthoptera were recorded on the sparsely vegetated disc-harrowed strips and eight on the controls (Table 1). All species apart from C. brunneus and M. maculatus were in low abundance (<20 adults). Common green grasshop- Nymphs x 2018 = S 02019 a a & ay 5 = Myrmeleotettix maculatus = 250 = S 200 = 2018 3S 150 Es 02019 § 100 = 50 0 Chorthippus brunneus @2018 02019 Mean adults/0.lha Control Disc harrowed Treatment Fig. 2. Nymph (both species combined) and adult density for two grasshopper species. 129 Table 1. Species of Orthoptera recorded on disc-harrowed strips and unmanaged controls. Species Disc-harrowed Control Total Chorthippus brunneus 434 295 729 Myrmeleotettix maculatus 552 7 559 Stenobothrus lineatus 15 16 31 Omocestus viridulus 4 16 20 Roeseliana roeselii 0 11 1 Pseudochorthippus parallelus 2 5 7 Chorthippus albomarginatus 0 3 3 Conocephalus fuscus 0 2 2 Total 1007 355 1362 per, Omocestus viridulus, lesser marsh grasshopper, Chorthippus al- bomarginatus, meadow grasshopper, Pseudochorthippus parallelus, and stripe-winged grasshopper, Stenobothrus lineatus, were all more numerous on the controls than the disc-harrowed strips (Table 1). No bush-crickets were recorded on the harrowed strips, with long- winged conehead, Conocephalus fuscus, and Roesel’s bush-cricket, Roeseliana roeselii, being confined to the taller vegetation (>30 cm) of the control heath. Despite the differing species lists, disc har- rowing had no impact on species richness (F = 3.46, P = 0.14) nor did it differ with years (F = 0.54, P = 0.50), with no interaction between treatment or year (F = 0.76, P = 0.43). Discussion In many grasslands, grazing can create patches of bare earth (through trampling of the soil by hooves) that provides an en- vironment for grasshopper oviposition and basking (Bazelet and Gardiner 2018, Gardiner 2018b). In the absence of grazing animals, such as sheep and cattle, artificial methods of soil dis- turbance can be used to establish exposed soil (Robertson and Hawkes 2017, Hawkes et al. 2019a,b). In this study, disc harrow- ing was utilized to encourage the germination of rare plant species such as A. glabra in Breckland. In turn, it appears that disc harrow- ing also benefited the localized grasshopper M. maculatus, which is a species found in early successional ground with bare earth and lichen cover (Marshall and Haes 1988). In this study, M. maculatus was almost exclusively found on the soil disturbed strips when compared to unmanaged dry heath, a similar situation to other Breckland soil disturbance studies. In research plots at nearby Stanford Training Area (STANTA), 60 M. maculatus were recorded in pitfall traps on cultivated grass heath, whereas none were captured in undisturbed controls (Rob- ert Hawkes personal communication). The grasshopper is at an advantage on exposed soil, particularly where there is a high stone content, due to its mottled coloration that provides excellent cam- ouflage (Gardiner 2014). In the pioneering Breckland study by Dolman and Sutherland (1994), shallow rotavation produced bare soil interspersed with fragments of vegetation including the remains of grass tussocks, moss, and lichen. It appears that disc harrowing produces a simi- lar diverse habitat. The microhabitats of the harrowed strips var- ied from unvegetated mobile sand, stony ground, to soil sparsely covered with lichens and mosses. Myrmeleotettix maculatus was re- corded in all of these situations (Fig. 3), and it is likely that the continued presence of this localized grasshopper may be depend- ent on the provision of an appropriate matrix of exposed soil and early successional vegetation in Breckland. The most abundant grasshopper, C. brunneus, had no pref- erence for the disc-harrowed strips. In a study of its response to sward height in Essex, C. brunneus preferred grasslands with swards JOURNAL OF ORTHOPTERA RESEARCH 2020, 29(2) Fig. 3. Typical Myrmeleotettix maculatus habitat: stony, exposed soil with little vegetation. Photo credit: T. Gardiner. 10-20 cm in height (Gardiner et al. 2002), suggesting that the har- rowed strips lacked the required patches of tall grass for shelter and feeding (Bernays and Chapman 1970a,b), despite an abun- dance of oviposition habitat. Consequently, without taller refuges from the often excessive microclimatic temperatures of bare soil, larger species (C. brunneus at 15-25 mm as compared to M. macu- latus at 12-19 mm; Marshall and Haes 1988) may disperse to un- managed vegetation to seek shade (Gardiner and Hassall 2009). The 2.5 m-wide strips were probably too narrow to fulfil all the needs of either grasshopper species, probably with frequent move- ments between the exposed soil and adjacent grass heath. Adults of M. maculatus were abundant on the strips: perhaps they utilized the exposed ground for basking and oviposition. In reality, soil disturbance is undertaken to conserve rarer species than the orthopterans recorded in this study. The pri- mary driver at Santon Warren is the conservation of the endan- gered plant A. glabra. The favorable habitat for M. maculatus demonstrates a knock-on benefit for a non-target insect. It is possible that disc harrowing may also benefit other inverte- brates that require soil disturbance, such as the declining small heath butterfly, Coenonympha pamphilus, that was regularly sighted on the strips. Green tiger beetles, Cicindela campestris, were also seen on the disc-harrowed strips along with many species of Hymenoptera. Hawkes et al. (2019a) report that ground-disturbance increased the numbers of woodlark, Lullula arborea, while multi-taxa inver- tebrate responses were mixed in response to various ground treat- ments (Hawkes et al. 2019b), with only ‘priority’ carabid beetles in- fluenced by cultivation treatment. Hawkes et al. (2019b) further out- lined that landscapes with soil disturbance treatments had a higher species richness of ants, beetles, and true bugs than those without. This small-scale study presents evidence that soil disturbance on a grass heath using a disc harrow may produce enhanced habi- tat for localized disturbance-dependent species such as M. macu- latus. Although orthopteran species richness was unaffected by disc harrowing, the strips may be too hot or bare of vegetation for species not recorded on the strips, such as the bush-crickets C. fuscus and R. roeselii (Table 1). Therefore, soil disturbance should be embedded within the management of a grass heath mosaic that includes long grassland benefitting the full range of Orthoptera present (Table 1). T. GARDINER Acknowledgements I would like to thank Neal Armour-Chelu of Forest Research, Forestry Commission, for providing much needed advice and infor- mation about the soil disturbance strips. Dr. Robert Hawkes of the University of East Anglia (UEA) offered advice on the response of in- vertebrates to soil disturbance interventions and also supplied sup- plementary data for M. maculatus from STANTA. Finally, I am thank- ful for constructive reviews from Dr. Dragan Chobanov and Luc Wil- lemse and to Dr. Maria-Marta Cigliano for her editorial guidance. References Ausden M, Treweek J (1995) Grasslands. In: Sutherland WJ, Hill DA (Eds) Managing Habitats for Conservation. Cambridge University Press, Cam- bridge, 197-229. https://doi.org/10.1017/CBO9781316036426.008 Bazelet CS, Gardiner T (2018) Orthoptera response to grazing: An intro- duction to the special issue. Journal of Orthoptera Research 27: 1-2. https://doi.org/10.3897/jor.27.27213 Bernays EA, Chapman RF (1970a) Experiments to determine the basis of food selection by Chorthippus parallelus (Zetterstedt) (Orthoptera: Acrididae) in the field. Journal of Animal Ecology 39: 761-776. https://doi.org/10.2307/2866 Bernays EA, Chapman RF (1970b) Food selection by Chorthippus parallelus (Zetterstedt) (Orthoptera: Acrididae) in the field. Journal of Animal Ecology 39: 383-394. https://doi.org/10.2307/2977 Berner D, K6rner Ch, Blanckenhorn WU (2004) Grasshopper populations across 2000 m of altitude: is there life history adaptation? Ecography 27: 733-740. https://doi.org/10.1111/j.0906-7590.2005.04012.x Choudhuri JCB (1958) Experimental studies on the choice of oviposition sites by two species of Chorthippus (Orthoptera: Acrididae). Journal of Animal Ecology 27: 201-215. https://doi.org/10.2307/2239 Dolman PM, Panter CJ, Mossman HL (2012) The biodiversity audit ap- proach challenges regional priorities and identifies a mismatch in conservation. Journal of Applied Ecology 49: 986-997. https://doi. org/10.1111/j.1365-2664.2012.02174.x Dolman PM, Sutherland WJ (1994) The use of soil disturbance in the management of Breckland grass heaths. Journal of Envi- ronmental Management 41: 123-140. https://doi.org/10.1006/ jema.1994.1038 Gardiner T (2010) Precipitation and habitat degradation influence the occurrence of the common green grasshopper Omocestus viridulus in southeastern England. Journal of Orthoptera Research 19: 315-326. https://doi.org/10.1665/034.019.0219 Gardiner T (2013) Grasshoppers of the Sandling Heathlands. Transactions of the Suffolk Naturalists’ Society 49: 23-32. Gardiner T (2014) Fire melanism of Myrmeleotettix maculatus Thunberg, 1815 (Orthoptera: Acrididae) at two heathland sites in Norfolk. Ento- mologist’s Gazette 65: 155-160. Gardiner T (2018a) Grasshoppers of Breckland: Classification and conser- vation. Journal of Breckland Studies 2: 20-27. Gardiner T (2018b) Grazing and Orthoptera: A review. Journal of Orthop- tera Research 27: 3-11. https://doi.org/10.3897/jor.27.26327 Gardiner T, Dover J (2008) Is microclimate important for Orthoptera in open landscapes? Journal of Insect Conservation 12: 705-709. https://doi.org/10.1007/s10841-007-9104-7 Gardiner T, Hassall M (2009) Does microclimate affect grasshopper popu- lations after cutting of hay in improved grassland? Journal of Insect Conservation 13: 97-102. https://doi.org/10.1007/s10841-007-9129-y Gardiner T, Hill J (2006) A comparison of three sampling techniques used to estimate the population density and assemblage diversity of Orthoptera. Journal of Orthoptera Research 15: 45-51. https://doi. org/10.1665/1082-6467(2006)15[45:ACOTST]2.0.CO;2 Gardiner T, Hill J, Chesmore D (2005) Review of the methods frequent- ly used to estimate the abundance of Orthoptera in grassland eco- systems. Journal of Insect Conservation 9: 151-173. https://doi. org/10.1007/s10841-005-2854-1 JOURNAL OF ORTHOPTERA RESEARCH 2020, 29(2) T. GARDINER Gardiner T, Pye M, Field R, Hill J (2002) The influence of sward height and vegetation composition in determining the habitat preferences of three Chorthippus species (Orthoptera: Acrididae) in Chelmsford, Essex, UK. Journal of Orthoptera Research 11: 207-213. https://doi. org/10.1665/1082-6467(2002)011[0207:TIOSHA]2.0.CO;2 Grayson FWL, Hassall M (1985) Effects of rabbit grazing on population variables of Chorthippus brunneus (Orthoptera). Oikos 44: 27-34. https://doi.org/10.2307/3544039 Hawkes RW, Smart J, Brown A, Jones H, Dolman PM (2019a) Experimental evidence that ground-disturbance benefits Woodlark Lullula arborea. Ibis 161: 447-452. https://doi.org/10.1111/ibi.12696 Hawkes R, Smart J, Brown A, Jones H, Lane S, Wells D, Dolman P (2019b) Multi-taxa consequences of management for an avian umbrella spe- cies. Biological Conservation 236: 192-201. https://doi.org/10.1016/j. biocon.2019.05.039 Heath D (1995) An Introduction to Experimental Design and Statistics for Biology. CRC Press, London, 384 pp. https://doi.org/10.1201/b12546 Key R (2000) Bare ground and the conservation of invertebrates. British Wildlife 11: 183-191. 131 Kohler G, Brodhun H-P, Schaller G (1987) Ecological energetics of Cen- tral European grasshoppers (Orthoptera: Acrididae). Oecologia 74: 112-121. https://doi.org/10.1007/BF00377354 Latchininsky A, Sword GA, Sergeev M, Cigliano MM, Lecog M (2011) Lo- custs and grasshoppers: Behavior, ecology and biogeography. Psyche 2011: 1-4. https://doi.org/10.1155/2011/578327 Marshall JA, Haes ECM (1988) Grasshoppers and Allied Insects of Great Britain and Ireland Harley Books, Colchester, 252 pp. Richmond D (2001) Grasshoppers and Allied Insects of Norfolk. Norfolk and Norwich Naturalists’ Society, Norwich, 64 pp. Robertson D, Hawkes R (2017) Nature conservation, ground disturbance and protecting archaeological remains on Brecks heaths. Journal of Breckland Studies 1: 68-79. Warren SD, Bittner R (2009) Active military training areas as refugia for disturbance-dependent endangered insects. Journal of Insect Conser- vation 12: 671-676. https://doi.org/10.1007/s10841-007-9109-2 Willott SJ (1997) Thermoregulation in four species of British grasshoppers (Orthoptera: Acrididae). Functional Ecology 11: 705-713. https://doi. org/10.1046/j.1365-2435.1997.00135.x JOURNAL OF ORTHOPTERA RESEARCH 2020, 29(2)