Linear features and butterﬂies: the importance of green lanes

Agriculture, Ecosystems and Environment 80 (2000) 227–242

Linear features and butterflies: the importance of green lanes

John Dovera,b,∗, Tim Sparksc, Sue Clarkeb, Kay Gobbettb, Sarah Glossopda Myerscough College, Bilsborrow, Preston PR3 0RY, UK

b The Game Conservancy Trust, Fordingbridge SP6 1EF, UKc NERC Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton PE17 2LS, UK

d Department of Environmental Management, University of Central Lancashire, Preston PR1 2HE, UK

Received 31 March 1999; received in revised form 16 December 1999; accepted 21 February 2000

Abstract

Green lanes are unmetalled tracks between fields of variable width, which may be sunk below or raised above field level,and bounded on both sides by ‘grass’ banks, hedgerows or dry-stone walls. In the UK they have no unique planning status andhave been overlooked as discrete landscape elements. Green lanes were surveyed for butterflies in 1997 on lowland arablefarmland on the Trafford/north Cheshire border (Warburton) and on upland grassland in the Yorkshire Dales (Ribble Valley).At the lowland site the green lanes were bounded by vegetation and were compared with grass banks and single hedgerowfield boundaries; at the upland farm, the green lanes were bounded by dry-stone walls and were compared with grass banksand single dry-stone walls. Data from earlier work on a largely arable farm (Manydown) in Hampshire in 1987 and 1988 werere-analysed to make comparisons between a green lane, the rides and glades of two coppiced woodlands, and the grass banksand single hedgerows surrounding arable fields. Green lanes, whether bounded by vegetation or stone were superior to othercommon farmland biotopes with the exception of woodland, in terms of both butterfly abundance and species richness.

Multiple regression of the Warburton data indicated the importance of green lanes, adjacent habitat type, and nectar sourcesfor species richness and butterfly abundance. The interior of green lanes had lower windspeeds, and more bramble nectarsources than hedgerows or grass banks. By their nature they occupy a larger area of uncropped land, and are subject to areduced disturbance regime and reduced inputs of agrochemicals and fertilisers. Their value as biodiversity reservoirs inintensively managed land is likely to be high. © 2000 Elsevier Science B.V. All rights reserved.

Keywords:Biodiversity; Butterfly abundance; Field margins; Nectar plants; Woodland; United Kingdom

1. Introduction

Information on butterfly distribution and abundancein farmland has increased in recent years in respectof field boundary habitats, field margins and manip-ulation of the crop (Dover, 1989; 1990, 1991, 1994,

∗ Corresponding author. Tel.:+44-1995-640611;fax: +44-1995-640842.E-mail address:[email protected] (J. Dover)

1996, 1997; Dover et al., 1990, 1997; Feber et al.,1994, 1996, 1997; Feber and Smith, 1995; Sparks andParish, 1995; de Snoo, 1996; Sparks et al., 1996). Mostof these studies relate to the typical habitats which sur-round arable crops such as woodland edge, hedgerows,and grass banks/verges; other habitats such as rail-ways and wetlands are cited less frequently. Recently,Dover et al. (1997) presented some evidence that thetracks between fields colloquially known as ‘greenlanes’ (Belsey, 1998) might be important for wildlife

0167-8809/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0167-8809(00)00149-3

228 J. Dover et al. / Agriculture, Ecosystems and Environment 80 (2000) 227–242

habitat, in a re-analysis of data from the Butterfly Mon-itoring Scheme transect for Woodwalton Farm. Thisfollowed from the suggestion of Dover (1996) that theshelter afforded by green lanes composed of a doubleline of hedges would be superior to single hedgerows.The definition of what constitutes a green lane is adifficult one (Belsey, 1998), as the width of the trackof a green lane may vary and be bounded by banks,ditches, hedges, scrub or dry-stone walls. The trackitself should be unmetalled, but that does not excludethe addition of hard-core to improve traction for farmmachinery. The variability of the boundary featuresand the exact nature and disturbance regime (includ-ing cutting) of the track are likely to impinge on thevalue of green lanes as wildlife habitat and hence thenumber, type and abundance of species within them.This paper addresses the question of whether greenlanes are superior, in terms of adult butterfly abun-dance and species richness, to simpler linear featuressuch as hedgerows, grass banks and drystone walls.

2. Methods

2.1. Study sites

Data from three study areas are presented here,varying in location and type from lowland arable farmsin Hampshire (Manydown) in the south of England

Fig. 1. Map of the Warburton study site in Trafford used for butterfly transects in 1997. The green lanes and other field margins (indicatedby dots) were divided up into 53 transect sections (not shown). Map not to scale.

and the Trafford/north-Cheshire border (Warburton)in the northwest, to upland farmland in the YorkshireDales (Ribble). The standard method of recording us-ing butterfly transects was used at all sites (Pollardet al., 1975; Hall, 1981).

2.1.1. WarburtonThe principal study area was in the Parish of War-

burton, Trafford (Nevell, 1997) contained within astrip of land bounded by the Manchester Ship Canalto the north, the River Bollin to the south, a metalledroad to the east and contiguous farmland to the west.The Warburton site (Fig. 1) was principally arableland with the main crops being cereals, with somecarrots and one large field of rough wet grassland.Field boundaries in Warburton were grass banks andhedgerows, with the green lanes bounded by a mix-ture of these habitats. In places the ‘hedgerows’ weremade principally of bramble, and some of the grassbanks were clearly relict hedgerows. The majority ofthe green lanes were at different levels from the fields,with some sunk to approximately 2 m below field levelin places (Fig. 2). Many of the green lanes and fieldboundaries can be clearly seen on an estate map of1751, with discontinuities in some fields showing thelikely positions of the individual strips in the formermedieval Town Field (Bayliss, 1996).

At Warburton the field boundaries and greenlanes were divided up into 53 sections reflecting

J. Dover et al. / Agriculture, Ecosystems and Environment 80 (2000) 227–242 229

Fig. 2. Cross-sections of green lanes used for butterfly transectsat the Warburton site in 1997. (a) Green lane at the same level asadjacent fields. (b) Green lane above adjacent field level on oneside, but below on the other. (c) Green lane below adjacent fieldlevel. Boundary vegetation varied from double hedges to grassbanks with intermittent scrub.

obvious physical changes such as aspect, vegetationand boundary type. Butterflies were recorded in 1997in the following four situations: along grass banksand hedgerows surrounding fields but not associatedwith green lanes (12 and 16 sections, respectively),‘outside’ green lanes, i.e. where green lanes werethe boundary habitats of fields (16 sections), and the‘inside’ of green lanes, i.e. along the track boundedby hedgerows/banks making up the green lane (ninesections) (Fig. 2).

2.1.2. RibbleA more limited study was carried out in the coun-

tryside surrounding the villages of Hellifield and LongPreston in the Ribble Valley of the Yorkshire Dales.The Ribble site was mainly grassland but with onearea backing on to household gardens. At the Ribblesite, field boundaries were typical for uplands in

England, being either grass banks or stone walls, withthe green lanes being bounded by stone walls.

At the Ribble site, the surveyed field boundarieswere less contiguous, and were deliberately selectedin 1997 to provide four replicates each of stone walls,grass banks and green lanes. The sites were dispersedover the countryside in a 4 km×2 km block of farm-land.

2.1.3. ManydownThe third study area was in north Hampshire and

was used by Dover et al. (1990) in their comparison ofconventional field margin management and the tech-nique known as ‘conservation headlands’. The farmwas principally arable, but with grass produced mainlyfor seed and for a small beef herd. The field boundaryhabitats were principally grass banks and hedgerowsbut the study also included transects through two cop-piced woodlands and a single green lane.

Data from Manydown was abstracted from tran-sects carried out in 1987 and 1988. The data on fieldmargins has been taken from the experimental con-trols used in the conservation headland evaluationsin 1987 and 1988 (Dover, 1991). The 1988 data wassupplemented by additional field margin data fromareas of the farm subject to normal farm practice butpreviously unpublished. Butterfly records from fieldmargins were made for their entire length and, there-fore, vary in both length of sampling unit and locationbetween the 2 years. In addition, data (also previ-ously unpublished) was collected from a woodlandtransect carried out over the same route in 1987 and1988 which included the rides and open glades of twodeciduous woodlands together with the ‘inside’ of agreen lane which abutted the larger of the two woods;these woods were used for butterfly dispersal stud-ies by Dover et al. (1992). Butterflies were recordedfrom this transect in 100 m length sections. The datafrom the two types of transect were integrated forbutterfly abundance analysis by correction for length.Comparisons of species richness have not been madeas they may not be reliable, because of the differentcollection methodologies employed.

2.2. Biotic and abiotic parameters

At the Warburton site, in addition to the abundanceof butterflies, records were made of variables which


Table 1Non-butterfly data recorded from the green lanes, hedgerows and grass banks in the Warburton study area 1997

Parameter Data type

Physical and associated featuresHabitat type Location of records: inside green lane, outside green lane,

single hedgerow, grass bank (presence/absence)Length of section In metresWindspeed Mean of start/finish records for each transect section (m s−1)Crop Type in adjacent field (presence/absence): grassland, cereals, carrots

Nectar plantsRagwort (Seneciospp.) No. of flowering stems/transect sectionBramble (Rubus fruticosusagg.) No. of metres/transect sectionThistle-like compositae (principallyCirsium spp.) No. of flowering stems/transect section

may have had an influence on butterfly distribution in-cluding, boundary type, crop, nectar plant abundance,etc. (Table 1).

2.3. Analysis

Kruskal–Wallis one-way analysis of variance(ANOVA), followed by multiple comparisons us-ing procedures in UNISTAT (Anon., 1995) whereappropriate, was used to compare butterfly abun-dance, species richness, nectar plant abundance, andwindspeed among the field margins, outside- andinside-components of green lanes, and woodlandrides. As no non-linear effects were expected from theabundance data it was standardised to numbers/100 mbefore analysis. However, as species richness isknown to exhibit non-linear effects with increasingtransect length (Sparks et al., 1997) data was stan-dardised to species richness/log transect length beforeanalysis. Warburton butterfly and habitat data werealso analysed using stepwise multiple regression.

3. Results

3.1. Warburton

Butterflies were recorded in the 53 transect sectionson five occasions in July and August 1997: 1062 in-dividuals of 15 species were found (Table 2).

3.1.1. AbundanceOverall, the outsides and insides of green lanes had

significantly more butterflies than either grass banks or

hedgerows, which did not themselves significantly dif-fer in butterfly abundance (Fig. 3a). When butterflieswere divided into ‘closed’ or ‘open’ population strat-egy groups there were differences evident between theoutside and the inside of green lanes for closed popula-tion species, with significantly more butterflies foundinside green lanes than outside; this difference was notevident for open population species (Fig. 3a). ‘Open’population species do not live in discrete colonies butdisperse continually from their natal patch, whereas‘closed’ population species live in discrete colonies(Thomas, 1984).

At the individual species level, the seven mostabundant species showed significant differencesamong habitat types: Meadow BrownManiola ju-rtina (L.) (P<0.01), GatekeeperPyronia tithonus(L.) (P<0.001), Wall Lassiommata megera(L.)(P<0.001), Speckled WoodPararge aegeria (L.)(P<0.01), Small TortoiseshellAglais urticae (L.)(P<0.05), PeacockInachis io (L.) (P<0.05) andthe Green-veined WhitePieris napi (L.) (P<0.001).Multiple comparisons (Fig. 4) showed several com-mon features. Hedgerows and grass banks were notshown to be significantly different from one anotherand the inside and outside of green lanes were notsignificantly different from one another except forthe Gatekeeper, where there were significantly morebutterflies inside the green lane. In every case, sig-nificantly more butterflies were found inside greenlanes than were associated with hedgerows or grassbanks. Some species differences did, however, occurin respect of other habitat comparisons. Thus, signifi-cantly more Meadow Brown, Small Tortoiseshell andGreen-veined White butterflies were associated with

J.D

over

et

al./A

gricu

lture,

Eco

system

sa

nd

Enviro

nm

en

t8

0(2

00

0)

22

7–

24

2231


Fig. 3. (a) Mean numbers of butterflies (±1 S.E.) in the four habitats studied at Warburton, Trafford in 1997 by population structure: allspecies: abundance of all butterfly species observed, closed species: species considered to have a closed population structure, open species:species considered to have an open population structure. Multiple comparison information following significant (P<0.05) Kruskal–Wallisone-way ANOVA given above bar charts as a matrix; G: grass banks, H: hedgerows, OGL: outside green lane, IGL: inside green lanes;n.s.: P>0.05, *: P<0.05; n.b.: additional shading categories given refer to later figures. (b) Mean butterfly species richness/log transectlength (±1 S.E.) (Sparks et al., 1997) in the four habitats studied at Warburton, Trafford in 1997 by population structure.


Fig. 4. Mean numbers (±1 S.E.) of seven butterfly species in the four habitats studied at Warburton, Trafford in 1997. See also Fig. 3.

the outsides of green lanes compared with grass banksand significantly more Wall, Speckled Wood andSmall Tortoiseshell butterflies were associated withthe outsides of green lanes compared with hedgerows.

3.1.2. Species richnessTotal butterfly species richness did not differ be-

tween grass banks and hedgerows, but both had

significantly fewer species than the outside or insideof green lanes. The inside of green lanes had signif-icantly more species than the outside. This patternof significant differences was repeated when specieswere classified into ‘closed’ population species,but ‘open’ population species did not differ signifi-cantly between the inside and outside of green lanes(Fig. 3b).


Fig. 5. Mean butterfly nectar plant richness (±1 S.E.) in the four habitats studied at Warburton, Trafford in 1997. Bramble: metres ofbramble/100 m; thistle: number of flowering stems of thistles and thistle like Compositae/100 m; ragwort: number of ragwort plants/100 m.See also Fig. 3.

3.1.3. Nectar plantsThe three main nectar plant groupings at the study

site were bramble (Rubus fruticosusagg.), ragwort(Seneciospp.) and thistle-like Compositae (Dover,1996). Ragwort abundance did not differ among thehabitat areas (P>0.05), but both bramble (P<0.001)and thistle-like Compositae (P<0.05) did. In multiplecomparisons, bramble differed significantly in everycombination except between hedgerows and grassbanks with most associated with the insides of greenlanes. Thistles only differed significantly betweenbanks or hedgerows and the insides of green lanes(Fig. 5).

3.1.4. WindspeedData was collected on four out of the five sample

dates. Data show some consistent trends, with wind-speed being lowest in the insides of green lanes andhighest in grass banks with hedgerows, and the outsideof green lanes intermediate in exposure (Fig. 6). Blus-tery conditions and differing windspeeds during thesurvey dates have contributed to data variability suchthat consistent significance levels have not been main-tained. Although it was not expected that there wouldbe separation of the hedgerows and outside of green

lanes, in 3 out of 4 days, windspeed appears slightlyhigher outside green lanes. This probably results fromthe variation in habitat structure from grass bank toscrub or hedgerow associated with this category.

3.1.5. Stepwise multiple regressionRegression analyses were carried out to examine

the importance of biotic and abiotic factors on the rawbutterfly data, as there were differences in adjacentcrop type, density of nectar sources, etc. Length waskept as a variable, rather than standardising the data tounit length. As expected this is a significant factor inthe majority of, but not all, analyses. Species richnesswas analysed using the total richness of butterflies atthe site, and also the data divided into open and closedspecies groupings. The results (Table 3) show the ex-pected dominance of the inside and outside of greenlanes, the importance of ragwort and also the positiveeffect of the rough grassland habitat. The poor habitatquality of grass banks and hedgerows are highlightedin the analysis by population structure.

The importance of the rough grassland habitat isreinforced in the analysis of total butterfly abundance(Table 4) along with the favourability of the inside ofgreen lanes and nectar sources. Individual analysis of


Fig. 6. Windspeeds (±1 S.E.), recorded on four of the five sample days, in the four habitats studied at Warburton, Trafford in 1997. Seealso Fig. 3.

the most abundant butterfly species (Tables 5–7) high-light different factors for each species, but consistentfactors include the inside of green lanes, rough grass-land, and nectar sources.

3.2. Ribble valley

Butterflies were recorded in the 12 transect sectionson 10 occasions between late July and mid-September1997. A total of 151 individuals of eight species were

Table 3Factors affecting the number of species of butterfly in the field margins and green lanes of the Warburton study area 1997a,b

All species Open population species Closed population species

Variable Regressionr2 F-valuec Variable Regressionr2 F-valuec Variable Regressionr2 F-valuec

name coefficient at end name coefficient at end name coefficient at end

Constant −0.8230 Constant 3.7016 Constant −1.3913Inside GL 3.5226 25.25 33.25 c Ragwort stems 4.6767 17.23 6.28 a Inside GL 1.2873 31.83 12.84 cOutside GL 1.9430 49.23 14.54 c Grass bank −1.6339 29.57 18.57 c Rough grass 2.5679 48.24 18.89 cRagwort stems 6.8031 57.07 5.27 a Single hedge−1.2059 42.97 11.51 b Ragwort stems 3.8841 59.05 6.35 aRough grass 2.8669 61.62 6.17 a Grass bank−0.6167 63.92 4.97 aLog length 1.6975 64.88 4.37 a Log length 0.9772 67.13 5.27 a

Bramble 0.8464 69.72 3.93 n

a Length of transect section transformed by log (x+1) prior to analysis.b n=P>0.05; a=P<0.05, b=P<0.01, c=P<0.001. Entry into equation set at 3.84;r2 values cumulative.c Residual ms from final model used as denominator.

recorded (Table 2); six species had open populationstrategies and made up 75% of records. Because of thesmall number of butterfly records, abundance compar-isons were made only at the population structure level(Fig. 7).

3.2.1. AbundanceTotal abundance of butterflies for the insides of

green lanes was significantly higher than for singlestone walls which, in turn, had significantly more


Table 4Factors affecting the abundance of butterflies in the field margins and green lanes of the Warburton study area 1997; data grouped intoabundance of all species, open population species and closed population speciesa

All butterflies Open population species Closed population species

Variable Regressionr2 F-valueb Variable Regressionr2 F-valueb Variable Regressionr2 F-valueb


Constant −12.3327 Constant −5.5741 Constant −3.0352Rough grass 64.8287 32.17 17.05 c Length 0.0944 28.33 13.18 c Rough grass 28.7101 46.83 72.16 cLength 0.1550 55.01 32.94 c Rough grass 44.4257 50.41 12.49 c Length 0.0275 59.34 14.73 cInside GL 25.6141 65.31 15.82 c Inside GL 16.9957 60.43 10.60 b Inside GL 6.3094 68.05 13.36 cThistle stems 3.2352 69.69 6.93 a Thistle stems 2.4461 65.47 6.25 a

Ragwort stems 61.3534 68.47 4.47 a

a a=P<0.05, b=P<0.01, c=P<0.001. Entry into equation set at 3.84;r2 values cumulative.b Residual ms from final model used as denominator.

butterflies than grass banks (Fig. 7). Open populationsubdivision of the data followed the same pattern asfor total abundance. However, in the closed popula-tion subdivision grass banks and stone walls werenot significantly different, probably because of lowbutterfly incidence (Fig. 7).

3.2.2. Species richnessOnly eight species were recorded at the Ribble Val-

ley site, reflecting the harsher upland grassland cli-mate compared with the more diverse lowland sitesof Warburton and Manydown, and no significant dif-ferences in species richness/log length (Sparks et al.,1997) were detected for any of the population strategygroupings, or for the overall data set (P>0.05).

3.3. Manydown

Butterflies were recorded in three grass banks andfour hedgerows around cereal fields in 1987 and four

Table 5Factors affecting the abundance of three species of Satyrid butterfly in the field margins and green lanes of the Warburton study area 1997a

Meadow Brown Gatekeeper Wall

Variable Regressionr2 F-valueb Variable Regressionr2 F-valueb Variable Regressionr2 F-valueb


Constant −1.3445 Constant 0.0000 Constant −0.1796Rough grass 21.0968 61.83 89.20 c Inside GL 2.5393 25.19 12.37 c Ragwort stems 4.3526 36.89 10.52 bLength 0.0128 66.74 7.38 b Ragwort stems 11.6032 39.96 12.30 c Bramble 1.0605 48.84 13.44 c

Length 0.0028 54.00 5.49 a

a a=P<0.05, b=P<0.01, c=P<0.001. Entry into equation set at 3.84,r2 values cumulative.b Residual ms from final model used as denominator.

grass banks and eight hedgerows in 1988; there were15 woodland ride/glade sections and six in the greenlane in both years. Records, taken at comparable timesbetween May and September for the arable and wood-land transect types, were made on 13 occasions in1987 and 10 in 1988; 776 individuals of 18 specieswere found in 1987 and 818 individuals of 17 speciesin 1988 (Table 2).

3.3.1. AbundanceIn 1987, the total abundance data showed that the in-

terior of the green lane and woodland rides/glades hadsignificantly more butterflies than hedgerows or grassbanks; that woodland rides/glades did not differ sig-nificantly from the green lane; and that hedgerows didnot differ significantly from grass banks. There weredifferences in abundance pattern between the closedand open population groupings. The closed populationgrouping showed exactly the same pattern as the totalabundance data. The open population grouping failed


Table 6Factors affecting the abundance of two species of Nymphalid butterfly in the field margins and green lanes of the Warburton study area 1997a

Small Tortoiseshell Peacock

Variable name Regression coefficientr2 F-valueb at end Variable name Regression coefficientr2 F-valueb at end

Constant −2.1262 Constant −2.1719Ragwort stems 62.8399 29.60 12.14 b Length 0.0276 37.85 42.54 cRough grass 21.6347 52.93 7.67 b Rough grass 6.2154 51.32 6.38 aThistle stems 1.5233 56.45 6.28 a Inside GL 3.7367 61.69 13.72 cLength 0.0365 60.31 5.11 a Thistle stems 0.3828 64.61 3.95 aInside GL 6.7522 63.66 4.33 a


Table 7Factors affecting the abundance of two species of Pierid butterfly in the field margins and green lanes of the Warburton study area 1997a

Small White Green-veined White

Variable name Regression coefficientr2 F-valueb at end Variable name Regression coefficientr2 F-valueb at end

Constant −0.3016 Constant −0.3469Length 0.0135 30.38 21.56 c Rough grass 19.1048 47.03 62.93 cInside GL 2.0996 41.07 9.07 b Inside GL 4.1509 57.78 11.39 b

Length 0.0128 62.57 6.27 a


Fig. 7. Mean numbers of butterflies (±1 S.E.) in the three habitats studied at the Ribble site, Yorkshire in 1997 by population structure;G: grass banks, SW: stone wall, ISGL: inside stone walled green lane. See also Fig. 3.


Fig. 8. Mean numbers of butterflies (±1 S.E.) by population structure in the four habitats studied at Manydown, Hampshire: (a) in 1987;(b) in 1988; G: grass banks; H: hedgerow; IGL: inside green lane; WR: woodland ride/glade. See also Fig. 3.

to show significant differences between hedgerowsand grass banks, or woodland rides and either the grassbanks or the hedgerows. There were, however, signif-icantly more butterflies associated with the inside of

the green lane compared with the woodland rides, thehedgerows and the grass banks (Fig. 8a).

In 1988, few significant differences were evidentin the total abundance data; although there were


significantly more butterflies associated with wood-land rides and the inside of the green lane than withgrass banks (Fig. 8b). Further analysis showed nosignificant differences in the open population data(P>0.05), whereas the closed population data exactlymirrored those for 1987.

3.3.2. Species richnessIn both years, the species richness trend fol-

lowed the same pattern (data in parentheses for 1987and 1988, respectively) Woodland rides/glades (15,14)>green lane (15, 12)>hedgerows (13, 11)>grassbanks (7, 9).

4. Discussion

The data presented here show clearly that greenlanes, whether bounded by vegetative material orstone, are important in terms of butterfly abundanceand species richness within a farmed landscape. Greenlanes as a whole benefit both open and closed popu-lation species, but are likely to be of particular valueto closed population species.

The most fundamental aspect of green lanes is theirphysical structure — the green lanes under study var-ied in their composition but included raised and sunkentrackways and, compared with hedgerows or grassbanks, these had substantially larger uncropped vergespotentially providing more breeding habitat. The sim-ilar responses of butterflies when stone walls wereused as hedgerow equivalents, and double stone wallsas green lanes, suggest that the nature of the boundaryof a green lane is not critical, but that the attributes en-closed within, and resulting from, parallel structuresare significant and are likely to result, in part, from themodification of the local climate. Enhanced shelter(Dover et al., 1997) is likely to be an important factorin the use of green lanes by butterflies, but the shortstudy of windspeeds reported here has shown sub-stantial daily variation in the data among field margintypes, and the responses of butterflies may be com-plex with activity thresholds depending on individualspecies’ response to windspeed, temperature, and winddirection relative to the boundary orientation, type andstructure. The comparisons of grass banks, hedgerows,green lanes, woodland rides and glades suggest a

relationship between butterfly abundance/speciesrichness and increasing structural complexity of thehabitat and the area of uncropped land it contains.

Floral factors from the studies reported here whichappear to influence the abundance of butterflies in-clude elevated numbers of nectar sources. In the caseof bramble, there was significantly more of this plantinside green lanes than in the other habitats stud-ied and its influence on butterfly distribution mayresult simply from there being potentially twice asmuch bramble habitat available in a double-hedgedgreen lane compared with a single hedgerow. Otherspecies’ distributions may result from a complexof factors. For example, the density of thistle-likespecies at Warburton was lower inside green lanescompared with hedgerows, yet higher compared withgrass banks. This could result from a two-stage pro-cess: initially, greater opportunities for establishmentof species such as creeping thistle (Cirsium vulgareL.) are created through soil or vegetation disturbancein field margins because of close ploughing and/orspray drift and subsequently, herbicide sprays re-duce the density of thistles more effectively in grassbanks than in hedgerows because of easier equipmenthandling or spray targeting.

Hedgerows are frequently cited as potential move-ment corridors for wildlife (Dawson, 1994) and withtheir enhanced habitat and shelter, the interiors ofgreen lanes may be superior to hedgerows in aid-ing dispersal. Work on carabid beetles in France hasshown the importance of lanes with double hedgesfor maintenance and movement of populations (Burel,1989). The slopes of sunken/raised banks associatedwith green lanes may also provide potentially valuablesites for butterfly thermo-regulation (basking) and en-hanced microclimates.

Although insides of green lanes have been shownto be superior in butterfly abundance to grass banksor single hedges/stone walls in three separate studies,the Warburton data, where the field-facing sides ofgreen lanes were included in the study, showed thatin some cases the outsides of green lanes were alsosuperior. The outside of a green lane may have anenhanced butterfly complement by association, withbutterflies moving from the inside to the outside totake advantage of changing patterns of sunlight and toexploit nectar sources. The extent to which localisedrearrangement takes place may vary between species


with, for example, the Gatekeeper being very stronglyassociated with the inside of green lanes. The basalvegetation on the outside of a hedge when part of agreen lane may also have different attributes to thatof a hedge acting as a boundary separating two fieldsand this may influence butterfly distribution. For ex-ample, a different nutrient status may result from theabsence of manure or artificial fertilizer use inside thegreen lane and affect plant bulk, density and speciescomposition. The adjacent crop/land use is also likelyto be an important influence on butterfly abundanceand species richness as the positive influence of roughgrassland in the regression analyses of the Warburtonbutterfly data has shown. This result may also becaused by localised movement of butterflies betweenthe adjacent land and boundary structures, which inturn may reflect the intensity of land management.

At the lowland sites of Warburton and Manydowngrass banks and hedgerows were not shown to dif-fer significantly in butterfly abundance, althoughdata trends showed higher numbers of butterflies inhedgerows. The enhanced shelter and additional nec-tar resources provided by hedges compared with grassbanks might have been expected to have resulted inlarger differences in butterfly abundance than was evi-dent (Dover, 1996; Dover et al., 1997). Butterflies tendto rise from vegetation in response to an observer’smovement along a transect and butterflies may be-come available for counting more readily in grassbanks than in hedgerows where the observer’s move-ment is obscured by the hedge. Comparisons of but-terfly abundance between hedgerows and grass banksusing transect techniques may, therefore, be subjectto a bias, where only one side of a field boundary isstudied, with a general tendency to overestimate abun-dance in field boundaries composed of grass banks.However, data from the upland site (Ribble valley)did show significant differences between stone wallsand grass banks for open population species; proba-bly a result of the much harsher upland environmentmaking grass banks a much less favourable habitatfor butterflies compared with lowland equivalents.

Hedgerows and grass banks have been identified inthe past as being important for biodiversity and as bi-ological pest control reservoirs, with new structuressuch as beetle banks developed purely to enhance thenatural control of invertebrate pests of cereal crops(Thomas and Wratten, 1988; Thomas, 1989). Green

lanes are likely to receive lower inputs of fertiliserand spray drift and may act as botanical reservoirs inintensively managed land. If the value of green lanesfor butterflies is an indication of their wider biodi-versity value, then their importance in the landscapemay be very high, especially for declining specieswhich rely on perennial vegetation such as bumblebees(Corbet, 1995). However, in common with all featuresin a man-made landscape they need to be sympatheti-cally managed to optimise their wildlife potential. Forgreen lanes this may include the periodic cutting ofboundary hedges to ensure that they do not becometoo shaded, rebuilding of stone walls and rotationalcutting of vegetation to prevent scrub invasion. Fur-ther study is required to identify the physical featuresof green lanes that are of most benefit to the butter-fly fauna and the management necessary to maintainthem.

In the UK, green lanes have received virtually noattention in ecological studies, although they are thesubject of many highways and rights-of-way legisla-tion (Belsey, 1998) and some are recognised as cul-tural monuments with some ancient trackways be-lieved to be in excess of 2000 years old (Belsey, 1998).Belsey (1998) cites data collected in 1976 giving totallength of green lanes and unsurfaced roads in Eng-land and Wales as 8480 km. Data on the current statusof green lanes — numbers, length, area, distribution,quality, and degree of degradation — are unavailable.Green lanes are not recognised as a specific landscapeelement in the Countryside Survey 1990 (Barr et al.,1993) or in the current round of fieldwork for theCountryside Survey 2000. As a result, there is no in-formation on changes in green lane abundance andquality in the way that there is for hedgerows (Barret al., 1993); for all practical purposes green lanes areinvisible in the planning/landscape protection arena.

Green lanes represent a large uncropped and unin-tensively managed land area compared with the samelength of hedgerow or grass bank, and where delin-eated by shrubs, a potential doubling of hedgerow vol-ume. As many green lanes are bounded by hedgerows,they are under threat in the same way as are hedges.However, the recent introduction of the UK HedgerowRegulations (1997) (DOE, 1997) where they arespecifically mentioned is likely to reduce this threat.Quality reduction of green lanes through the cessa-tion of management through abandonment, or their


surfacing by tar, concrete, hard-core or other mate-rials are also likely to reduce their value. The recentincrease in interest in off-road motoring and othererosive countryside pursuits are also a threat to theecological value of green lanes, and a reclassificationof their highway status may be required where this issevere (Belsey, 1998).

Green lanes are clearly important landscape ele-ments, but this importance has only been recognisedin their amenity, aesthetic, recreational and cultural di-mensions. It is also likely that they are of high biodi-versity value, particularly given their position withinintensively managed land; if this proves to be the casethen an enhanced protection status is justified. Thereis clearly an urgent need for further studies of greenlanes embracing a wider range of target species.

Acknowledgements

The authors thank Mr. B. Johnston of theCo-operative Society, Mr. H.R. Oliver-Bellasis of theManydown Estate, Mr. and Mrs. D. Priestner, and Mr.Winder for access to the study areas. We are gratefulto two anonymous referees whose comments greatlyimproved the draft manuscript. Work at the Many-down Estate was supported by the Game ConservancyTrust and NERC Special Topics in Agriculture andthe Environment Award G2/044.

References

Anonymous, 1995. Unistat Version 4 for Windows User’s Guide.Unistat Ltd., London.

Barr, C.J., Bunce, R.G.H., Clarke, R.T., Fuller, R.M., Furse, M.T.,Gillespie, M.K., Groom, G.B., Hallam, C.J., Hornung, M.,Howard, D.C., Ness, M.J., 1993. Countryside Survey 1990.Main Report. Department of the Environment, London.

Bayliss, D., 1996. Historical Atlas of Trafford. Don Bayliss,Altrincham.

Belsey, V., 1998. The Green Lanes of England. Green Books Ltd.,Totnes.

Burel, F., 1989. Landscape structure effects on carabid beetlesspatial patterns in western France. Landscape Ecol. 2, 215–226.

Corbet, S.A., 1995. Insects, plants and succession: advantages oflonger-term set aside. Agric. Ecosyst. Environ. 53, 201–217.

Dawson, D., 1994. Are Habitat Corridors Conduits for Animals andPlants in a Fragmented Landscape? A Review of the ScientificEvidence. English Nature, Peterborough.

de Snoo, G.R., 1996. Non-target insects in unsprayed cereal edgesand aphid dispersal to the adjacent crop. J. Appl. Entomol. 120,501–504.

DOE, 1997. The Hedgerow Regulations. HMSO, London.Dover, J.W., 1989. The use of flowers by butterflies foraging in

cereal field margins. Entomologist’s Gazette 40, 283–291.Dover, J.W., 1990. Butterflies and wildlife corridors. In: Nodder,

C. (Ed.), The Game Conservancy Review of 1989. The GameConservancy, Fordingbridge, pp. 62–64.

Dover, J.W., 1991. The Conservation of insects on arable farmland.In: Collins, N.M., Thomas, J.A. (Eds.), The Conservationof Insects and Their Habitats. Academic Press, London,pp. 294–318.

Dover, J.W., 1994. Arable field margins: factors affecting butterflydistribution and abundance. In: Boatman, N.D. (Ed.), FieldMargins: Integrating Agriculture and Conservation. British CropProtection Council, Warwick, England, pp. 59–66.

Dover, J.W., 1996. Factors affecting the distribution of butterflieson arable farmland. J. Appl. Ecol. 33, 723–734.

Dover, J.W., 1997. Conservation headlands: effects on butterflydistribution and behaviour. Agric. Ecosyst. Environ. 63, 31–49.

Dover, J., Sotherton, N., Gobbett, K., 1990. Reduced pesticideinputs on cereal field margins: the effects on butterflyabundance. Ecol. Entomol. 15, 17–24.

Dover, J.W., Clarke, S.A., Rew, L., 1992. Habitats and movementpatterns of satyrid butterflies (Lepidoptera: Satyridae) on arablefarmland. Entomologist’s Gazette 43, 29–44.

Dover, J.W., Sparks, T.H., Greatorex-Davies, J.N., 1997. Theimportance of shelter for butterflies in open landscapes. J. InsectConserv. 1, 89–97.

Feber, R., Smith, H., 1995. Butterfly conservation on arablefarmland. In: Pullin, A.S (Ed.), Ecology and the Conservationof Butterflies. Chapman & Hall, London, pp. 84–97.

Feber, R.E., Smith, H., Macdonald, D.W., 1994. The effects of fieldmargin restoration on the meadow brown butterfly (Maniolajurtina). In: Boatman, N.D. (Ed.), Field Margins: IntegratingAgriculture and Conservation. British Crop Protection Council,Warwick, England, pp. 295–300.

Feber, R.E., Smith, H., Macdonald, D.W., 1996. The effects onbutterfly abundance of the management of uncropped edges ofarable fields. J. Appl. Ecol. 33, 1191–1205.

Feber, R., Firbank, L., Johnson, P.J., Macdonald, D.W., 1997.The effect of organic farming on pest and non-pest butterflyabundance. Agric. Ecosyst. Environ. 64, 133–139.

Hall, M.L., 1981. Butterfly Monitoring Scheme: Instructions forindependent recorders. Institute of Terrestrial Ecology, AbbotsRipton.

Nevell, M., 1997. The Archaeology of Trafford: A Study of theOrigins of Community in North West England Before 1900.Trafford Metropolitan Borough Council, Sale.

Pollard, E., Elias, D.O., Skelton, M.J., Thomas, J.A., 1975. Amethod of assessing the abundance of butterflies in MonksWood National Nature Reserve in 1973. Entomologist’s Gazette26, 79–88.

Sparks, T.H., Parish, T., 1995. Factors affecting the abundanceof butterflies in field boundaries in Swavesey fens,Cambridgeshire, UK. Biol. Conserv. 73, 221–227.


Sparks, T.H., Bellamy, P.E., Eversham, B.C., Greatorex-Davies,J.N., Hinsley, S.A., Jones, S.M., Mountford, J.O., 1996. Theeffects of three hedge management treatments on the wildlife ofa Cambridgeshire hedgerow. Aspects Appl. Biol. 44, 277–284.

Sparks, T.H., Mountford, J.O., Manchester, S.J., Rothery, P.,Treweek, J.R., 1997. Sample size for estimating species listsin vegetation surveys. The Statistician 46, 253–260.

Thomas, J.A., 1984. The conservation of butterflies in temperatecountries: past efforts and lessons for the future. In:

Vane-Wright, R.I., Ackery, P.R. (Eds.), The Biology ofButterflies. Academic Press, London, pp. 333–353.

Thomas, M.B., 1989. The creation of habitat islands to enhancepopulations of beneficial insects. In: Proceedings of BCPCConference, Vol. 37, 1989, pp. 1097–1102.

Thomas, M.B., Wratten, S.D., 1988. Manipulating the arablecrop environment to enhance the activity of predatory insects.Aspects Appl. Biol. 17, 57–66.

Linear features and butterﬂies: the importance of green lanes

Documents

Transcript of Linear features and butterﬂies: the importance of green lanes