The ideal aim of rewilding is to restore natural processes to create ‘self-willed’ ecosystems involving the creation of large areas of habitat subject to stochastic disturbance, connected by favorable corridors for species to disperse along. Reversion of arable farmland to grassland and scrub habitats on Black Bourn Valley nature reserve in Suffolk (south-east England) through non-intervention allowed succession to occur largely unmanaged. Fields in the early stages of rewilding (4–14 years) are found at Black Bourn Valley, while pond creation has been extensive since 2010, creating water edge habitat and heterogeneity to the re-establishing grassland. Monitoring of Orthoptera revealed statistical evidence that species diversity/richness and field grasshopper Chorthippus brunneus (Thunberg, 1815), meadow grasshopper Pseudochorthippus parallelus (Zetterstedt, 1821), common groundhopper Tetrix undulata (Sowerby, 1806) and slender groundhopper Tetrix subulata (Linnaeus, 1758) were in higher abundance in fields ≥8 years since arable cropping ceased compared to those 4 years post reversion. Fields ≥8 years old were probably favorable due to the presence of microhabitats for basking and egg-laying orthopterans that included ant hills, sparsely vegetated pond edge and open swards with an abundance of fine-leaved grasses (Agrostis and Festuca spp.) and a low abundance of leaf litter. Lagomorph grazing by wild brown hare Lepus europaeus and rabbit Oryctoloagus cuniculus was critical in maintaining exposed soil for Orthoptera in the older fields, while deer paths appeared to create microhabitats that may be utilized by Orthoptera. We postulate that rewilding schemes on arable farmland should use a Rewilding Max approach and avoid the frequent usage of domestic livestock, relying on wild lagomorph and ungulate grazers to maintain an open mosaic habitat structure with only intermittent cattle, horse, or sheep grazing.

Acrididae, biodiversity, bush-cricket, conservation, deer, grasshopper, Tettigoniidae, ungulate, wilding

Orthoptera form an important part of grassland ecosystems across Europe (Köhler et al. 1987, Ingrisch and Köhler 1998, Humbert et al. 2009). Orders such as Orthoptera (grasshoppers, bush-crickets, and crickets) are an important component of invertebrate assemblages in agricultural ecosystems, particularly as prey for bird and spider species (Joern 1986, Belovsky and Slade 1993, Oedekoven and Joern 1998). Gardiner et al. (2002) suggest that intensively managed farmland habitats such as arable fields, heavily grazed improved pastures, and hay meadows have a low abundance of orthopteran species such as meadow grasshopper Pseudochorthippus parallelus (Zetterstedt, 1821) and field grasshopper Chorthippus brunneus (Thunberg, 1815). To reverse the decline of insects such as grasshoppers and bush crickets, rewilding of arable farmland may be highly beneficial.

The term rewilding was first used in North America in the 1980s (Noss 1985). Soulé and Noss (1998) proposed three key components of rewilding: large core protected areas, ecological connectivity, and keystone species that translated to the 3Cs of cores, corridors, and carnivores. Over time, Soulé and Noss’s original concept has shifted into local interpretations but still incorporates self-regulatory ecosystems with minimal or no anthropogenic influence where wild grazers have a critical role (Dempsey 2021).

The role of wild herbivore grazers, such as lagomorphs (e.g., rabbit Oryctoloagus cuniculus) and ungulates (e.g., deer), in managing rewilded grasslands has not been studied in any depth with the aim of rewilding to recreate ‘natural’ ecosystems (Gordon et al. 2021b). Deer laydown areas and paths represent variation in sward height and could therefore be an influence on sward structure important for Orthoptera. Mixed approaches (e.g., relying on natural processes and introducing domestic grazers) with only minimal conservation intervention can be successful and may be necessary in some situations where non-intervention is not suitable (e.g., urban edge).

In recent times, the aim of rewilding in the UK has focused on restoring natural processes by creating large areas of habitat subject to stochastic disturbance connected by favorable corridors for species to disperse along (Carver and Convery 2021, Gordon et al. 2021a, b). Such ecological restoration on agricultural land that allows habitats to regenerate with a lack of active farmland (e.g., fertiliser application) or conservation management such as controlled livestock grazing is known as Rewilding Max (Gordon et al. 2021a,b). Domestic livestock (cattle, sheep, and ponies) are often used to graze rewilded farmland sites (e.g., Knepp Wildland in West Sussex, UK (Dempsey (2021)) after the initial establishment phase and grassland re-establishment (Casey et al. 2020). This form of conservation intervention without sole reliance on natural grazers is known as Rewilding Lite (Gordon et al. 2021b). However, introduced livestock can have detrimental impacts on Orthoptera where stocking density is too high and resultant sward height too short (Gardiner and Haines 2008). Across Europe, homogenously short swards established by overgrazing is the greatest threat to Orthoptera (affecting 262 species; Hochkirch et al. 2016). The consequences of livestock grazing are largely influenced by the intensity of grazing, type of grazer, and rotational or seasonal aspects of the regime, which in turn have an impact on characteristics of grasslands, such as leaf litter development, plant species presence, sward height, and vegetation biomass (Marini et al. 2008, Fabriciusová et al. 2011, Fonderflick et al. 2014, Rada et al. 2014, Kurtogullari et al. 2020).

The abundance of Orthoptera, particularly grasshoppers, is strongly influenced by sward height, biomass, and the composition and the availability of bare earth (Clarke 1948, Gardiner et al. 2002). Increased herbage biomass and sward height through abandonment of grassland management on rewilded sites could lead to a concomitant decrease in sward temperatures and extinction of light near the soil surface, particularly where leaf litter is allowed to develop (Gardiner et al. 2005). This is an important factor in Orthoptera distribution, as Van Wingerden et al. (1992) suggest that the number of grasshopper species is reduced in such ‘cold’ grasslands due to slow egg development and delayed hatching, particularly where there is a dense leaf litter layer (Gardiner et al. 2005). In these tall and dense grasslands, the availability of bare earth for the basking and oviposition needs of Orthoptera is often provided by ant hills where eggs are laid and nymphs are found in spring (Richards and Waloff 1954). In European grasslands on abandoned arable land, some authors (e.g., King 2006, 2020, 2021) consider the yellow-meadow ant Lasius flavus to be a keystone species due to the bare earth habitat provided by its large mounds of earth.

Orthoptera are ideal for monitoring the effects of rewilding at sites due to established, easily repeated monitoring methods, speed of response to habitat change, and range of species with differing habitat requirements (e.g., bare earth, short grass, tall grass, and scrub species) (Gardiner et al. 2005). Using a simple acoustic and visual transect methodology accompanied by habitat measurements (e.g., sward height and bare earth), we would expect there to be a strong species-specific response to rewilding features (e.g., ant hills) and wild grazing. For example, C. brunneus may require the bare earth of ant hills for basking and oviposition, while common green grasshopper Omocestus viridulus (Linnaeus, 1758) is a species of tall grassland that may benefit from an absence of lagomorph grazing (Marshall and Haes 1988).

The aim of this paper is to report on a study of the orthopteran assemblage of rewilded grassland on former arable farmland in Black Bourn Valley in Suffolk, UK. Results are discussed in relation to natural grazing pressure (brown hare, rabbit, and deer), grassland age since reversion commenced, and other factors such as sward height and bare earth habitat provided by ant hills and pond banks.

Study site.—Black Bourn Valley has been owned and managed by Suffolk Wildlife Trust (SWT) since 1995 (it was formerly known as Grove Farm) in Suffolk, UK (52°15'0.4644"N, 0°51'1.422"E). The reserve is 119 ha in area and was previously intensively cropped for agriculture with nitrogen (N) fertilizer applied to a range of annual crops, including winter wheat. The Black Bourn River runs along the eastern edge of the reserve and is adjoined by riverside meadows (outside the scope of this study). The soil is a lime-rich loam and clay with slightly impeded drainage and moderate fertility. The farm had 11 farm ponds extant when SWT acquired the site in 1995. Nine new ponds have been created since 2010 as part of the Freshwater Habitats Trust’s (FHT) Million Ponds Project. These ponds have several notably scarce and rare plants (e.g., tassel stonewort Tolypella intricata) for which the reserve has been designated a Flagship Pond Site by the FHT.

A total of eight fields were selected for this study due to their differing ages since reversion. Five fields were last plowed and cropped in 2017, two fields were last cropped in 2013, and one was cropped in 2007 (Fig. 1, Table 1). Once cropping ceased, all fields were allowed to naturally revert to grassland and scrub through succession with minimal intervention apart from mowing of footpaths and occasional light grazing (not on an annual basis). Throughout the duration of the 2021 summer study period, there was no active conservation management of any of the fields. A green lane ran through the site, and most fields were surrounded by scrubs or dense hedgerows. There were 10 ponds in the fields last cropped in 2013 or earlier (combined pond area 953 m²) and six in the fields last cropped in 2017 (combined pond area 562 m²). Most of the ponds had gently shelving banks (25–50° angle) and were sparsely vegetated.

Fig. 1. 

Layout of the eight experimental fields at Black Bourn Valley with ponds and corridor habitats highlighted.

Transect surveys.—A 1-m wide × 400-m long transect was established in all eight fields. Transects were arranged in a W shape (each arm 100 m) to ensure even coverage of each field and avoid any edge habitat effects. The transect method closely followed the methodology of Gardiner et al. (2005), Gardiner and Hill (2006), and Gardiner (2021). Each transect was walked at a slow, strolling pace (2 km/hr) on 3 occasions from May–August 2021. Adult individuals of all Orthoptera species along all transects were recorded acoustically and visually to determine assemblage composition and species diversity and richness.

Nymphs flushed from a 1-m wide band in front of the observer were recorded along all transects. As it is difficult to distinguish between species in the early instars (though not impossible, see Thommen 2021), numbers for nymphs of all species were lumped together for recording purposes. The surveys were undertaken in vegetation sufficiently short (<50 cm) to minimize the possibility of overlooking nymphs in tall grass or non-stridulating species such as groundhoppers (Tetrigidae) (Gardiner et al. 2005). With practice, it was relatively easy to ascertain the species of adults without capture (Gardiner and Hill 2006), although some species, such as long-winged conehead Conocephalus fuscus (Fabricius, 1793) and Roesel’s bush-cricket Roeseliana roeselii (Hagenbach, 1822), are significantly under-recorded using visual transects (Gardiner and Hill 2006). A dual visual and acoustic monitoring method has been used by Weiss et al. (2013) to ensure complete coverage of the orthopteran fauna of sites. In the current study, a stridulation monitoring technique was used to record adult males of species that stridulated along the transects at the same time as visual monitoring by flushing. Stridulation monitoring has been used to record cryptic species in Essex and has been found to be effective compared to visual sighting transects and pitfall traps (Harvey and Gardiner 2006, Gardiner et al. 2010). Bat detectors were not required in the current study as the first author (TG) was able to reliably detect stridulating males up to 20 m away either side of the transect. The weather conditions on survey days were favorable for insect activity, being largely sunny and warm (>17°C).

Natural grazing pressure and habitat characteristics surveys.—A total of 40 sward heights were recorded at random positions along the Orthoptera transects using a 1-m rule for each of the eight fields in early September 2021. In each field, ant hills were counted along the 400 m long Orthoptera transects in a 1-m wide band; additionally, the number of individual wild lagomorph (differences between brown hare and rabbit were not determined, so droppings pooled for both species) droppings (dung balls) were recorded in the same 1-m band to ascertain the level of grazing pressure in the fields (Wood 1988, Gibb and Fitzgerald 1998, Millett and Edmondson 2013).

Four of the six British ungulate species have been recorded at Black Bourn Valley: fallow deer Dama dama, muntjac Muntiacus reevesi, red deer Cervus elaphus, and roe deer Capreolus capreolus. Due to the known presence of ungulates on site, individual deer pellets (not classified to species) were counted along a 5-m wide × 200-m long transect in each field in October 2021 when the vegetation had died back, allowing easy sighting of fecal matter. The counting of deer droppings (droppings of all species lumped together for analysis) followed the methods of Marques et al. (2001). In addition to the dropping counts, deer laydown areas (flattened areas of grass at least 2 × 2-m in area) and deer paths (parted grass through vegetation) were recorded where they were observed within the 5 × 200-m transect in each field.

In the fields where arable cropping ceased in 2017 and in 2013 or 2007, 2 × 2-m quadrats were randomly surveyed (11 and 7 quadrats, respectively) to collect vegetation data. The number of quadrats surveyed in both field types was approximately proportionate to the number of fields studied in each (i.e., 5/8 fields for 2013 or 2007 = 63%, 11/18 quadrats = 61%). Each plant species recorded in a quadrat, along with bare earth and leaf litter (dead and decaying vegetative material, typically grass in this study), was given a DOMIN value in accordance with National Vegetation Classification survey methods (Rodwell 2006). The DOMIN scale assigns percentage cover of species or habitat features to a numeric grade using the following scale: 1, <4% few individuals; 2, <4% several individuals; 3, <4% many individuals; 4, 4–10%; 5, 11–25%; 6, 26–33%; 7, 34–50%; 8, 51–75%; 9, 76–90%; 10, 91–100% (Rodwell 2006).

Nine species of Orthoptera were recorded on the Black Bourn Valley reserve, including three species uncommon in this area of Suffolk (Table 2). The most commonly recorded species were P. parallelus (21% of adult detections) and R. roeselii (20%), followed by C. fuscus (19%) and C. brunneus (12%). Less common species included O. viridulus and slender groundhopper Tetrix subulata (Linnaeus, 1758) (10% each). The common groundhopper Tetrix undulata (Sowerby, 1806) and lesser marsh grasshopper Chorthippus albomarginatus (De Geer, 1773) were found in much lower abundance (3%), while the dark bush cricket Pholidoptera griseoaptera (De Geer, 1773) was a rarity (1%).

The abundance of 6 of the 9 species (C. albomarginatus, C. brunneus, O. viridulus, P. parallelus, T. subulata, and T. undulata) was highest in one field (Kiln Meadow, cropping ceased 2013; Figs 1, 7) where 30% of the total detections of adult Orthoptera were recorded. For O. viridulus, T. subulata, and T. undulata, a very high percentage of the total recorded adults for each species were from Kiln Meadow and Further Thurston combined (82%, 89%, and 73%, respectively). For P. griseoaptera, 83% of adults were recorded from Miller’s Field (cropping ceased in 2007).

There was very strong evidence (p < 0.001) that species richness and diversity and the abundance of T. undulata were significantly higher in fields ≥8 years since cropping cessation compared to those only 4 years since cropping ceased (Table 2). There was moderate evidence (p < 0.05) that C. brunneus and P. parallelus were significantly more abundant in fields ≥8 years old and only weak evidence (p < 0.10) for T. subulata (Table 2). Very strong evidence (p < 0.001) indicated that the most abundant species (% of total number) in each field was significantly higher in the younger fields (c. 43%) compared to the older fields (c. 22%). In 4 out of the 5 fields 4 years post-cropping, C. fuscus was the most abundant orthopteran, comprising c. 43% of the total number of Orthoptera overall across the 5 younger fields. In 2 out of the 3 older fields (≥8 years post-cropping), P. parallelus was the most abundant species, forming 20.6% of overall sightings. In these older fields, C. fuscus comprised only 11.3% of adults.

There was moderate evidence (p < 0.05) that ant hill density, lagomorph droppings, and the number of ponds were significantly higher in fields ≥8 years since cropping cessation (Table 3). Contrastingly, there was very strong evidence (p < 0.001) that leaf litter was significantly less abundant in fields ≥8 years since cropping cessation. Only weak evidence was obtained that there was a higher number of deer paths in the older fields (p < 0.10).

Of the five most abundant plant species, two were significantly more numerous in fields ≥8 years since cropping cessation: creeping bent Agrostis stolonifera (moderate evidence) and red fescue Festuca rubra (very strong evidence; Table 4). Overall plant species richness was also significantly higher (very strong evidence) in the older fields (Table 4). In contrast, soft brome Bromus hordeaceus was more abundant in fields 4 years post-cropping (strong evidence). Two species, Yorkshire fog Holcus lanatus and bristly ox-tongue Helminthotheca echioides, had similar abundance in both types of field, as did bryophytes (Table 4).

Intensive agriculture has significantly reduced the diversity and abundance of Orthoptera on UK farmland (Gardiner et al. 2002, Cherrill 2010, 2015). Taking less agriculturally productive land out of arable cropping and allowing it to naturally regenerate (Rewilding Max) with minimal domestic livestock grazing and only wild grazing by lagomorphs and ungulates can produce swards that are quickly colonized (c. 4–8 years) by Orthoptera species not usually found on farmland, such as O. viridulus or T. undulata. Rewilded fields should incorporate features such as old and restored ponds to provide bare earth bank habitat for groundhoppers (e.g., T. subulata), while ant hills develop as the grassland matures, providing exposed soil and shorter swards for basking and ovipositing grasshoppers (e.g., C. brunneus). Lagomorph grazing in and around ponds and ant hills enhances the value of these bare earth features by maintaining them at an early successional stage. Of course, the response is species specific, and here the heterogeneity of micro-habitat is important to cater for short (e.g., T. undulata) and tall grassland (e.g., O. viridulus) species. A patchwork of different swards may also help to promote the highest diversity of insects (Kruess and Tscharntke 2002).

The authors would like to thank Suffolk Wildlife Trust for supporting the project and giving permission to survey the fields. We would also like to extend our gratitude to the Suffolk Naturalists’ Society for funding the research through their Morley Grant Scheme. Professor Rob Fuller kindly helped with the discussion and review of the draft manuscript, while Anna Saltmarsh and Joanna Hodgson assisted with the fieldwork. Prof. Axel Hochkirch and an anonymous reviewer provided very constructive reviews of this paper.