Providing evidence to improve practice

Action: Manage hedgerows to benefit wildlife (includes no spray, gap-filling and laying)

Key messages

 

Supporting evidence from individual studies

1 

A study of nine farms in England and one in Scotland from 1979 to 1981 (Rands 1987) found that the most suitable nesting habitat for grey partridge Perdix perdix was in hedges trimmed biennially compared to those unmanaged, occasionally managed, cut annually, sides cut annually, boundaries with verges cut or regularly grazed. Grey partridge breeding density and recruitment increased with the length of field boundary, amount of dead grass and height of earth bank at the hedge base. Nests were sited where dead grass, bramble and leaf litter were significantly more abundant and bank height was higher. Field boundaries and hedges were surveyed in late winter. Breeding density was surveyed in March. Four farms were searched for nests and nest success was recorded.  Forty-two grey partridge nests were recorded. Hedge characteristics were recorded around each nest and at a randomly chosen 'non-nest' site within 100 m.

 

2 

A replicated, controlled, randomized study of 14 hedges at ten sites throughout Northern Ireland in 1991 (McAdam, Bell & Henry 1994) found that hard coppicing increased numbers of plant species and laying increased numbers of invertebrate species. Treatments had higher numbers of plant species/plot compared to the control (26), but this was only significant for coppicing (with planting in gaps; 31-34), not pollarding (28) or laying (27). There were significantly more invertebrate orders in laid hedges (4.1) than the control (2.6). Numbers in coppiced (3.6-3.8) and pollarded (3.2) hedges did not differ significantly from the control. There were similar numbers of plant species and invertebrate orders in Environmentally Sensitive Area and non-Environmentally Sensitive Area hedges.  The 14 hedges were dominated by hawthorn Crataegus monogyna, had 150 m of uniform height and density of trees, had permanent pasture on both sides and were largely overgrown and unmanaged. The five treatments were applied to 25 m lengths of each hedge. Hedges were fenced to exclude grazing and were cut to 1.5 m each third year where appropriate. Plants were listed within each plot during the summer. Invertebrates were sampled using shelter traps (20 x 5 cm) in the hedgerow canopy during May. Additional plant data are available for 1992 and 1994 (McAdam et al. 1996).

3 

In the same study as McAdam et al. 1994, McAdam et al. 1996 found that although hard coppicing, pollarding (to 1.5 m) and laying initially increased plant species diversity, after four years it had no effect on species richness. In 1991, two treatments had more plant species than the control (25; coppicing: 31-33; pollarding 28); the exception was laying (27).  By 1994, although more species were recorded from all treatments than the control (23), none were significantly different (coppicing: 25-26; laying: 25; pollarding: 25).  In 1991, the six Environmentally Sensitive Area and eight non-Environmentally Sensitive Area hedges both had a mean of 20 plant species. Environmentally Sensitive Area hedges coppiced with mixed planting had significantly more species than control Environmentally Sensitive Area hedges (23 vs 19). By 1994, Environmentally Sensitive Area sites had slightly higher diversity than non-Environmentally Sensitive Area sites (1992: 21 vs 20; 1994: 22 vs 20).

4 

A replicated study of hedgerows in Cambridgeshire, UK (Sparks & Martin 1999) found that hawthorn Crataegus monogyna berry yield was significantly higher in unmanaged hedgerows than those that were laid (and trimmed after 5 years) or coppiced (and trimmed after 5 years) or pollarded to 1.5 m. Yield decreased with more extreme management treatments (unmanaged: 148-161 g/2.5 m²; laid: 48-85 g/2.5 m²; coppiced: 3 g/2.5 m²; pollarded: 2 g/2.5 m²). There was some compensation for reduced hawthorn yields in laid and coppiced hedgerows through increased rose hip yields, although rose hip samples were too small for analysis. There were no significant differences between laid (84 g/2.5 m²) and laid and trimmed hedgerows (86 g/2.5 m²); the two hedgerow treatments were visually difficult to separate. The weights of 50 berries were lighter in coppiced plots (11 g) than all other treatments (15-16 g). There were no significant differences in berry dry matter content between treatments (45-51%). Hawthorn and rose Rosa canina agg. berries were harvested from three to eight replicates in October 1997. Hedgerows were laid or coppiced in 1990-1991 and were trimmed or pollarded in 1995-1996. Berries were harvested within each plot (20-40m long sections) from five 50 × 50 cm quadrats on the side of hedges, 1m above ground.

5 

A 2000 literature review (Aebischer, Green & Evans 2000) found that the UK population of cirl bunting Emberiza cirlus increased from between 118 and 132 pairs in 1989 to 453 pairs in 1998 following a series of schemes designed to provide overwinter stubbles, grass margins, and beneficially managed hedges and set-aside. Numbers on fields under these schemes increased by 70%, compared with a 2% increase elsewhere.

6 

A replicated study of hedgerows within seven arable and pastoral farms in England and Wales (Maudsley, Marshall & West 2000) found that cutting frequency and timing affected invertebrate numbers but not plant diversity. Abundance of individual invertebrate groups tended to decline with regular hedge cutting. However, although numbers of some taxa such as jumping plant lice (Psyllids) were higher in uncut sections, cutting increased others, notably herbivores and detritivores such as true bugs (Heteroptera; uncut: 4/plot; annual: 22-28; biennial: 15-23), beetles (Coleoptera; uncut: 4/plot; annual: 5-9; biennial: 8-13), springtails (Collembola) and thrips (Thysanoptera). Cutting in February rather than September reduced numbers of butterflies and moths (Lepidoptera; 33 vs 65/plot) and flies (Diptera; 82 vs 118/plot), but increased beetles (Coleoptera; 9-13 vs 5-8) the following summer. Cutting frequency (uncut, annual, biennial and triennial) and timing did not affect numbers of plant species in the hedge or hedge base. Hedge dimensions were greatest on annually cut hedges and smallest on those uncut. The longer the hedge was left between cuts, the more berries were produced (uncut, biennial, annual). Berry numbers were reduced with triennial cuts. Each hedgerow received replicated treatments (15-21) of each cutting frequency and timing. Data were obtained on the abundance of berries (autumn), shrubs, hedge-base flora and invertebrates (May and July) within each hedgerow plot. The same study is presented in Marshall et al. 2001.

Additional reference

Marshall, E. J. P., Maudsley, M. J., West, T. M. and Rowcliffe, H. R. (2001) Effects of management on the biodiversity of English hedgerows. 361-365 in: C. Barr and S. Petit (eds) Hedgerows of the World: Their Ecological Functions in Different Landscapes, International Association for Landscape Ecology, 10th Annual Conference of the International Association for Landscape Ecology. September 2001, Birmingham, UK.

 

7 

A replicated study of hedgerows in Cambridgeshire and Warwickshire, England (Sparks, Robinson & Downing 2000) (same site as (Sparks & Martin 1999)) found that hawthorn Crataegus monogyna berry yield was significantly reduced when management involved removing fruit-bearing wood.  Yield was significantly higher in sections that had been laid (282 g/2.5 m²) or uncut (219-421) than those that had been cut (4-10), coppiced (3-26) pollarded (70) or grubbed out (0). Yield differences were due to greater numbers of berries rather than increased berry size. At Monks Wood, the dry matter content was significantly higher in uncut sections; this was not the case at Drayton. At Drayton there were five randomized replicate plots (12 m long) of the following five treatments: unfenced or fenced control cut annually; fenced uncut; coppiced; grubbed out and replanted with blackthorn. At Monks Wood, there were two randomized trials each of 10-12 (20 m long) plots that received 3-5 replicates of three (uncut, coppiced or laid) or two (uncut or pollarded to 1.5 m) treatments. Berries were harvested within each plot from five 50 × 50 cm quadrats on the side of hedges, 1 m above ground.

 

8 

A replicated, controlled study of three hedgerows in farmland at Long Ashton Research Station, Somerset (Marshall, West & Maudsley 2001) found that hedgerow management, particularly sowing perennial seed mix, increased botanical diversity in the hedge base.  Plant species diversity in sown plots was significantly higher than in plots where the hedge was cut, in two arable fields (17-38 vs. 13-27 species in sown and unsown plots respectively) and one grassland field (23-27 vs 16-23). In the grassland field, there was little difference between treatments (unmanaged: 15-21; autumn cut: 16-23; selective herbicide: 17-23; no fertilizer: 19-24) and the initial increase in number of plant species in the sown plot did not persist. In the cereal fields plots sown without selective herbicides tended to have more plant species than plots sown with selective herbicides (18-27 vs 16-23). There was no overall difference between number of plant species in autumn- (14-26 species) and spring-cut hedges (13-27). Excluding fertilizer (13-31 plant species) and applying selective herbicide (17-29 plant species) tended to increase the number of plant species, although the initial increase due to fertilizer exclusion only persisted in one of the two arable fields. Total herbicide application initially reduced the number of plant species to four, but species rapidly recovered (15-24). The number of true bug (Heteroptera) species was higher in plots treated with selective herbicide than other treatments (grassland: 10 vs 7 true bug species with and without selective herbicide respectively; arable: 5 vs 1-3). Three hedgerows with low botanical diversity and high annual weed densities were selected. Treatments were applied to consecutive 1 m wide plots along each hedge bottom. Vascular plants were recorded in May and July-August 1997-1999.  Invertebrates were sampled using a D-Vac suction sampler (four 5-second samples).

 

9 

A site comparison study of 60 hedgerows on two neighbouring arable farms in Wiltshire, UK (Moonen & Marshall 2001) found that coppiced and gapped-up hedges had the greatest number of plant species (23 species on average) followed by those with adjacent sown grass and grass/wildflower strips (2, 4 or 20m wide; Manor Farm: 17 species) and those with a 0.5 m sterile strip created with a broad-spectrum herbicide (Noland’s Farm: 15 species). Hedges with adjacent sown strips had a lower abundance of pernicious weed species. The composition of woody species within hedges did not differ between the two farms (Manor Farm: 22 woody species, Noland’s Farm: 16 woody species). All 23 sampled hedges on Noland’s Farm were trimmed annually and had the vegetation at the hedge base cut. The 37 sampled hedges on Manor Farm were trimmed in alternate years, and nine were coppiced and gapped-up. Hedge vegetation was assessed in 25 m long plots in the middle of a field edge, on both sides of each hedge, in June 1996.

10 

A replicated site comparison study of hedgerows at two arable and one mixed farm in England (Croxton & Sparks 2002) found that berry yield was significantly higher in hedges managed but uncut for at least two years (143-175 g/2.5 m²) than those cut annually (4-11 g/2.5 m²), but both had significantly lower yields than those uncut for many years (305-530 g/2.5 m²). There was no significant difference in the percentage dry matter content between treatments (uncut: 36-42% dry matter; uncut ? two years: 34-44%; annual cut: 35-41%). The farms were in Yorkshire, Cambridgeshire and Buckinghamshire (mixed). Five hedges of each cutting regime were identified per site. Hawthorn berries were harvested (September-October 2001) from 10 quadrats (50 × 50 cm) on the side of hedges, 1 m above ground and at 10 m intervals (or the next nearest hawthorn to 10 m).

11 

A small replicated, controlled study from May-June in 1992-1998 in one experimental area with managed hedges (3 km²) and four conventionally managed arable farms in Leicestershire, England (Stoate 2002) found that the abundance of nationally declining songbird species and species of conservation concern significantly increased through time in the site with managed hedges. Although there was no overall difference in bird abundance, species richness or diversity between the experimental and control sites, numbers of nationally declining species rose by 102 % (except for Eurasian skylark Alauda arvensis and yellowhammer Emberiza citrinella). Nationally stable species rose (insignificantly) by 47 % (with eight species exhibiting net increases, especially greenfinch Carduelis chloris 68%, and four species exhibiting net decreases). The author concluded that managing hedges to increase shrubby vegetation, as part of an integrated management package, provides the greatest benefits to species of conservation concern but does not affect species diversity at the farm scale.

12 

A review of the literature on the impacts of agricultural management on bats, their habitats and invertebrate prey in Europe (Bat Conservation Trust 2003) found one study that reported complex impacts on invertebrates from management that affects hedgerow structure (see Maudsley, Marshall & West 2000).

 

13 

A replicated study of 751 hedges restored under 100 Countryside Stewardship Scheme agreement and 774 hedges restored under 100 Environmentally Sensitive Area agreements in England investigated the effects on the hedgerow network over five years (Catherine Bickmore Associates 2004). Limited data were presented comparing biodiversity pre- and post-works.  Overall, the majority of hedges under the agreements were less than 2 m wide at the base (Countryside Stewardship Scheme: 65%; Environmentally Sensitive Area: 81%) and under 2 m tall (Countryside Stewardship Scheme: 48%; Environmentally Sensitive Area: 57%). Trees were present in 53-56% of hedges. Overall, 21% of Countryside Stewardship Scheme and 38% of Environmentally Sensitive Area hedges were classified as species-rich (compared to an average of 26% of hedges in England). The average number of basal flora species per hedge was six species under Countryside Stewardship Scheme and eight under Environmentally Sensitive Area agreements. Significantly more pre-works hedges were over 2m in height (Countryside Stewardship Scheme: 53%; Environmentally Sensitive Area: 62%) compared to post-works hedges (Countryside Stewardship Scheme: 28%; Environmentally Sensitive Area: 34%). Under Environmentally Sensitive Area agreements, significantly more pre-works hedges were over 2 m wide (20%) than post-work hedges (11%). Countryside Stewardship Scheme hedges with a high structural variability tended to be pre-works (16 vs 12%) including hedges of a gappy nature and of various heights. Only 11% of the pre-works Countryside Stewardship Scheme hedges were stock-proof, compared to 18% post-works. Hedges pre- and post-restoration works (coppicing, laying or planting) were sampled using the national local hedgerow procedure. A maximum of eight hedges were sampled from any one agreement.

14 

A replicated site comparison study (Herzoget al. 2005) found that on average 50% of hedgerows in Ecological Compensation Areas on farmland in the Swiss plateau were of ‘good ecological quality’ (based on national guidelines for Ecological Compensation Areas target vegetation).  Ecological quality was higher for Ecological Compensation Area hedges in the ‘pre-alpine hills’ zone than in the more intensively farmed ‘lowland’ zone, due to more old trees and fewer invading plants. The centres of territories of hedgerow birds were significantly more frequent in or near Ecological Compensation Area hedges (293 territories), suggesting that hedgerow birds were attracted to or favoured these areas. Plant species and hedgerow characteristics were recorded for 317 Ecological Compensation Area hedgerows (total length 44 km) in eleven study areas between 1998 and 2001. Territories of breeding birds were mapped in 23 study areas, based on three visits between mid-April and mid-June.

 

15 

A 2007 site comparison study on 23 sites in the lowlands north of the Alps, Switzerland (Birrer et al. 2007) found twenty-three out of one hundred hedges managed as Ecological Compensation Areas had at least one of the 37 surveyed bird species present, compared to 13/100 hedges outside the agri-environment scheme. The 23 sites (covering up to 3 km² each) were randomly selected and surveyed three times each between April and June in both years of study.

16 

A replicated, controlled trial of the Rural Stewardship agri-environment scheme on five farms in Scotland (Lye et al. 2009) found that hedgerows dominated by hawthorn Crataegus monogyna or blackthorn Prunus spinosa were less attractive than field margins or grasslands to nest-searching queen bumblebees Bombus spp. in April and May. There was no significant difference in numbers of foraging or nesting queens between hedgerows managed under the agri-environment scheme (winter cut every three years, gaps filled, vegetation below unmown and unsprayed) and conventionally managed hedgerows. The study took place before the woody species comprising the hedgerow came into flower. Nest-searching and foraging queen bumblebees were recorded on six 100 x 6 m transects on each farm, once a week from 14 April to 16 May 2009, on dry days with temperatures of 5-25°C. Each farm had two arable field margin transects, two grassland (non-boundary) transects, and two hawthorn- or blackthorn-dominated hedgerow transects. On farms with the Rural Stewardship Scheme, one of each transect type was under the agri-environment scheme.

 

17 

A replicated site comparison of 2,046 1 km² plots of lowland farmland in England in 2005 and 2008 (Davey et al. 2010a) (same study as Davey et al. 2010b) found that management of hedges and ditches under Entry Level Stewardship did not have clear impacts on farmland bird species. Management had significant positive impacts on five species in at least one region of England, but these effects were often very weak and four of the same species showed negative responses in other regions. The other five ‘hedgerow’ species investigated were never positively associated with boundary management. Generally, effects appeared to be more positive in the north of England.

 

18 

A 2010 site comparison study of 2,046 1 km² plots of lowland farmland in England (Davey et al. 2010b) (same study as Davey et al. 2010a) found that three years after the 2005 introduction of the Countryside Stewardship and Entry Level Stewardship schemes, there was no association between the length of hedgerow managed according to the agri-environment scheme and farmland bird numbers. Hedgerow specialist species, including the yellowhammer Emberiza citrinella and common whitethroat Sylvia communis, showed no significant population response, whereas there were greater numbers of starling on arable, pastoral and mixed farmland with hedgerow management. For example, in mixed farmland plots starling populations increased by 0.2 individuals for each 1 km of hedgerow. On the other hand, grey partridge Perdix perdix appeared to be detrimentally affected, with an apparent decline of 0.3 individuals for every 1.1 km of hedgerow managed according to the agri-environment schemes. The 2046 1 km² lowland plots were surveyed in both 2005 and 2008 and classified as arable, pastoral or mixed farmland. Eighty-four percent of plots included some area managed according to the Entry Level Stewardship or Countryside Stewardship Scheme. In both survey years, two surveys were conducted along a 2 km pre-selected transect route through each 1 km² square.

 

19 

A replicated study in February 2008 across 97, 1 km2 plots in East Anglia, England (Davey et al. 2010c) (part of the same study as (Davey, Vickery, Boatman, Chamberlain, Parry & Siriwardena 2010)) found that four farmland bird species showed strong positive responses to field boundaries managed under agri-environment schemes. These were blue tit Parus (Cyanistes) caeruleus, dunnock Prunella modularis, common whitethroat Sylvia communis and yellowhammer Emberiza citrinella. A further five (Eurasian blackbird Turdus merula, song thrush T. philomelos, Eurasian bullfinch Pyrrhula pyrrhula, long-tailed tits Aegithalos caudatus and winter wren Troglodytes troglodytes) showed weak positive responses and Eurasian reed buntings Emberiza schoeniclus showed a weak negative response. The boundaries were classed as either hedges, ditches or hedges and ditches and most were managed under the Entry Level Stewardship scheme.

 

20 

A replicated site comparison study on farms in two English regions (Field et al. 2010) found that summer yellowhammer Emberiza citrinella numbers were significantly higher in hedges under environmental stewardship management than in conventionally managed hedges. On East Anglian farms, this was true for both Entry Level Stewardship and Higher Level Stewardship hedge management options (estimated >1.5 yellowhammers/m in Higher Level Stewardship hedges compared to <0.5 yellowhammers/m in conventional hedges). On Cotswolds farms it was only true for hedges managed as ‘high environmental value hedges’ under Higher Level Stewardship (estimated 0.5 yellowhammers/m), while hedges managed under Entry Level Stewardship did not have more yellowhammers than conventional hedges (estimated <0.2 yellowhammers/m). Hedgerows managed under Entry Level Stewardship are cut every two or three years in winter only. Surveys were carried out in the summers of 2008 and 2009, on up to 30 Higher Level Stewardship farms and 15 non-stewardship farms in East Anglia, and up to 19 Higher Level Stewardship and 8 non-stewardship farms in the Cotswolds.

 

Referenced papers

Please cite as:

Dicks, L.V., Ashpole, J.E., Dänhardt, J., James, K., Jönsson, A., Randall, N., Showler, D.A., Smith, R.K., Turpie, S., Williams D.R. & Sutherland, W.J. (2017) Farmland Conservation Pages 245-284 in: W.J. Sutherland, L.V. Dicks, N. Ockendon & R.K. Smith (eds) What Works in Conservation 2017. Open Book Publishers, Cambridge, UK.