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Reading, Christopher J.; Jofré, Gabriela M.. 2015. Habitat use by smooth snakes on lowland heath managed using 'conservation grazing'. Herpetological Journal, 25 (4). 225-231.
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The NERC and CEH trademarks and logos (‘the Trademarks’) are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. 1 Habitat use by smooth snakes on lowland heath managed using
2 ‘conservation grazing’.
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10 Christopher J. Reading1 & Gabriela M. Jofré
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18 1 Centre for Ecology & Hydrology, CEH Wallingford, Benson Lane, Crowmarsh
19 Gifford, Wallingford, Oxon, OX10 8BB, UK
20 [email protected] : Corresponding author
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25 Running title: Habitat use by smooth snakes
1
1 ABSTRACT
2 Heathland in the UK, and parts of mainland Europe, is being managed increasingly by
3 landowners and statutory conservation bodies e.g. Natural England, using cattle grazing which
4 is often referred to as ‘conservation grazing’ in an attempt to justify its use in the absence of
5 any detailed prior research into its actual benefits for wildlife species, whose individual habitat
6 requirements are likely to vary, therefore requiring different management techniques to
7 conserve them. Over four years, between 2010 and 2013, cattle were excluded from six hectares
8 of lowland heath that had been subject to annual summer cattle grazing between May 1997 and
9 autumn 2009 and in which reptile numbers had been monitored annually since 1997. Changes
10 in smooth snake (Coronella austriaca) numbers were recorded annually in the ungrazed area
11 and in a four hectare area of heathland adjacent to it that continued to be grazed. The number
12 of individual smooth snakes, and the total number of smooth snake captures, were significantly
13 higher in the ungrazed heath than the grazed heath and were associated with increased habitat
14 structure, resulting principally from tall heathers and grasses. The results of the study suggest
15 that the use of cattle grazing as a management tool on lowland heath is detrimental to smooth
16 snake populations and that their recovery, following the cessation of grazing, may take many
17 years.
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19 Key words: Coronella austriaca, cattle grazing, habitat degradation, habitat structure,
20 Calluna vulgaris, Molinia caerulea, Ulex minor, Agrostis curtisii
21
22 INTRODUCTION
23 Habitat change is now recognised as a primary cause of declines in biodiversity generally and
24 the biggest threat to the conservation status of many taxa worldwide (Sala et al., 2000). In
25 particular, it is considered to be the main driver of global declines in herpetofauna (Gardner et
2
1 al., 2007). The causes of habitat change are various, often linked to human land use practices
2 and include forestry, agriculture and domestic livestock grazing (Lindenmayer & Fischer,
3 2006; Böhm et al., 2013). Livestock grazing has a direct impact on plant biomass, plant species
4 composition and vegetation structural components, such as height and cover which, together,
5 may affect a habitat’s ability to support the animal communities that rely on it for food and
6 shelter (Kie et al., 1996; Hay & Kicklighter, 2001).
7 Within the UK the lowland heaths of southern England have declined in area
8 significantly since 1759 (Rose et al., 2000) due mainly to fragmentation and the loss of many
9 resultant small areas to development. Heathland is also often viewed as ‘waste land’ and
10 Government policy, under the GAP (Grazing Animals Project) scheme, encourages its
11 exploitation. As a consequence, Natural England, the UK’s statutory body tasked with
12 protecting England’s fauna and flora, under direction from the UK Government’s Department
13 of Environment, Food and Rural Affairs developed a habitat management policy designed to
14 ‘conserve wildlife and maintain biodiversity’ (see NEa). This policy includes the use of
15 domestic livestock, primarily cattle, to manage lowland heath and encourages landowners to
16 do so by providing financial incentives, partly based on the size of areas to be grazed, under
17 the Higher Level Stewardship (HLS) scheme, part of the Environmental Stewardship (ES)
18 scheme (see NEb). To promote its acceptance by landowners and the general public this policy
19 has been called ‘conservation grazing’. Unfortunately, no investigation into its benefits for
20 wildlife species inhabiting lowland heath was undertaken prior to its implementation as a
21 management tool in the 1990’s, and so its impacts on them were unknown. However, evidence
22 from The Netherlands has shown that reptile populations either disappeared or declined
23 significantly (Strijbosch, 2002; Stumpel & van der Werf, 2012) in cattle grazed heathland
24 whilst a review of its impacts on heathland in north-west Europe concluded that more
3
1 monitoring and experimental research was required to establish its effectiveness as a
2 management technique (Newton et al., 2009).
3 In the UK, all six species of native British reptiles (adder Vipera berus, grass snake
4 Natrix natrix, smooth snake Coronella austriaca, common lizard Zootoca vivipara, sand lizard
5 Lacerta agilis, slow worm Anguis fragilis) occur on lowland heath in southern England, where
6 the smooth snake is restricted to it (Frazer, 1983) and where the sand lizard and smooth snake
7 (European protected species) are at the north-western edge of their geographical range.
8 In 2010, cattle were excluded from part of an area of heathland where the reptiles had
9 been studied intensively since 1997 and where habitat deterioration was the suggested cause of
10 a reported decline of smooth snakes between 1997 and 2009 (Reading et al., 2010). This
11 presented a rare opportunity to investigate the potentially changing relationship between habitat
12 structure and the occurrence of all six native species of British reptile on grazed and ungrazed
13 heath. Here we report on habitat use by smooth snakes and how their numbers have changed
14 since 2010.
15
16 MATERIALS AND METHODS
17 Study area
18 The study site was a 10 ha area of lowland heath situated within Wareham Forest, a managed
19 coniferous forest in the south of the UK (50o44′N, 2o08′W). The area is surrounded on three
20 sides by conifer plantations and on the fourth by heathland. The area comprises a mosaic of
21 dry and wet heath, the dry heath dominated by a discontinuous cover of ling (Calluna vulgaris),
22 bell heather (Erica cinerea), common gorse (Ulex europaeus) and dwarf gorse (Ulex minor),
23 and the wet heath by purple moor grass (Molinia caerulea) and cross-leaved heath (Erica
24 tetralix). Bristle bent (Agrostis curtisii), moss and dead grass leaves, of varying depth, also
25 occurred throughout the study site along with small areas of bare sandy ground in the dry heath.
4
1 The study area is part of a much larger area (approximately 300 ha) that has, since 1997,
2 been managed annually using cattle grazing between early May and mid-September. This area
3 includes a mixture of managed conifer plantations of varying age (0-60+ years old), heathland,
4 acid bog and forest rides. In February 2009 a small part of the study area (≈0.2 ha) was subject
5 to a controlled burn by the Forestry Commission. In February 2010 cattle were excluded from
6 approximately six hectares of the study area (hereafter referred to as ‘ungrazed’ area), with the
7 remaining four hectares (adjacent to it), including the partially burnt area, continuing to be
8 grazed (hereafter referred to as ‘grazed’ area).
9 Since May 1997 the number of cows released annually has varied between 35 and 91
10 individuals giving overall minimum cattle densities at the start of each season of 0.12-0.30
11 cows per hectare. These densities increased within each year following the birth of calves. The
12 cattle also split into small cohesive groups of up to 30 individuals that roamed, grazed and
13 rested together on preferred areas of heathland (heathland, conifer plantations, forest rides and
14 tracks but excluding bog). The breeds used were mainly Aberdeen-Angus crossed with
15 Hereford, Simmental and Friesian.
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17 Reptile surveys
18 Reptiles were surveyed using randomly placed arrays of 37 artificial refuges (corrugated steel
19 sheet: 76cm x 65cm), spaced 10m apart, and arranged in a hexagonal pattern with each array
20 covering an area of approximately 0.29 hectares (Reading, 1997). With the exception of 1997
21 (18 surveys) and 2002 (only 3 surveys due to injury) 21 surveys were completed annually
22 (1998-2013) between late April and late October (approximately one survey every 7-10 days).
23 There were five refuge arrays in the ungrazed area between 1997 and 2000 which was increased
24 to seven in 2001. There were four within the grazed area that had been continuously managed,
25 between 1997 and 2013, using cattle. The data from 2002 were excluded from the analysis.
5
1 During each survey each array was visited in sequence and a transect walk (360 m long)
2 completed within each array such that each refuge was visited in turn and checked for reptiles
3 on and under it. Reptiles observed during the walk between refuges were also identified and
4 recorded. To avoid checking the same array at approximately the same time of day, during each
5 survey, the starting point of each survey was varied. Captured smooth snakes were individually
6 identified using implanted passive integrated transponder (PIT) tags (see Reading, 2012 for a
7 detailed description of individual snake identification methodologies).
8
9 Vegetation surveys
10 Vegetation surveys were completed annually in late summer between 2010 and 2013 using a
11 2m x 2m quadrat at each of 10 fixed locations within each of the 11 reptile refuge arrays. The
12 location pattern of the 10 quadrats within each array was the same for all arrays. The height
13 and percent cover of each plant species (live and standing dead), depth of litter and proportion
14 of bare ground occurring within each quadrat were recorded. All height and depth
15 measurements were made using a one metre ruler and up to 12 measurements were taken for
16 each species in each quadrat depending on its abundance.
17 Overall the height/depth of 37 habitat variables (live plants, standing dead plants, litter)
18 and the percent cover of these, plus bare ground, were measured annually in each of the 110
19 fixed vegetation quadrats between 2010 and 2013 (Table 1). The habitat within each of the 11
20 reptile refuge arrays was subsequently classified, using the NVC, as either ‘Calluna vulgaris-
21 Ulex minor’ (Cv-Um) heath or ‘Ulex minor-Agrostis curtisii’ (Um-Ac) heath, the former being
22 characteristically dry lowland heath whilst the latter is wet lowland heath. Four of the ‘Cv-Um’
23 arrays and three of the ‘Um-Ac’ arrays were within the ungrazed area and two of each in the
24 grazed area.
25
6
1 Table 1 List of the 38 habitat variables, with abbreviations (Abbrev.), measured during each
2 vegetation survey. *-species selected for Fig. 2.
Abbrev. Species Abbrev. Species
Heathers Bushes Cv* Calluna vulgaris Ue Ulex europaeus D.Cv Standing dead C. vulgaris Um* Ulex minor Ec* Erica cinerea D.Um Standing dead U. minor D.Ec Standing dead E. cinerea Cs Cytisus scoparius Et* Erica tetralix Rp Rhododendron ponticum D.Et Standing dead E. tetralix Rf Rubus fruticosus agg. Grasses and Sedges Herbs Ac* Agrostis curtisii Dp Digitalis purpurea Acap Agrostis capillaris Pe Potentilla erecta Mc* Molinia caerulea Ra Rumex acetosella Mm Mibora minima Gs Galium saxatile Cp Carex pilulifera P Plantago sp. Sedge Carex sp. Sv Senecio vulgaris Trees Litter Pine Pinus sp. Pn Pine needles Bp Betula pendula DPa Dead P. aquilinum fronds Qr Quercus robur DGr Dead grass leaves Dw Dead wood Lower plants HLit Heather litter Pa Pteridium aquilinum GLit Gorse litter Fern Unidentified Fern Ci Cladonia impexa Other Moss* Unidentified Moss BGr Bare ground
3
4 Data analysis
5 All statistical analyses were completed using Minitab 16 (Minitab 2010). The type of heath
6 present in each refuge array was determined according to National Vegetation Classification
7 (NVC) criteria using TABLEFIT v.1.1 (Hill, 2011). Mean values were compared using
8 Student’s t-test and linear regression analysis was used to describe the relationships between
9 smooth snake occurrence and habitat variables. All statistical tests were considered significant
10 at P<0.05.
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7
1 RESULTS
2 Changes in smooth snake numbers (1997-2013)
3 The mean number of smooth snake individuals recorded annually from both grazed and
4 subsequently ungrazed arrays (after 2009), between 1997 and 2009, showed a small increase
5 after the introduction of cattle grazing in 1997, reaching a peak in 2000 in both (grazed:
6 mean=8.0; SD=2.00; n=4; ungrazed: mean=8.0; SD=1.581; n=5; Fig. 1). In both array subsets
7 the mean numbers then declined to a minimum in 2006 (grazed: mean=2.25; SD=1.258; n=4)
8 and 2007 (ungrazed: mean=3.71; SD=3.039; n=7) and remained at, or about, this level until
9 2009.
10
11 Fig. 1. Mean (± SE) number of individual smooth snakes (♀ + ♂) found in grazed (■: 1997-
12 2013, ●: 1997-2009) and ungrazed (○: 2010-2013) arrays. The vertical line shows when the
13 cattle exclusion fence was erected.
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1997 1999 2001 2003 2005 2007 2009 2011 2013 Year 14
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1 Following the exclusion of cattle in 2010 the mean number of smooth snakes occurring
2 in the ungrazed arrays increased to a maximum of 5.7 in 2012 (SD=3.450; n=7) before
3 declining back to 4.3 (SD=2.811; n=7) in 2013 whilst in the grazed arrays it declined to a
4 minimum in 2012 and 2013 (mean=1.50; SD=1.000; n=4). Prior to the exclusion of cattle the
5 mean number of individuals per array in the grazed and ungrazed array subsets, with the
6 exception of 2003, did not differ significantly (P>0.05). Following the exclusion of cattle there
7 was a divergent trend in the two array subsets with the mean numbers of individuals in the
8 ungrazed arrays in 2012 and 2013 being significantly greater than in the grazed arrays (2012:
9 t=-3.02, P=0.019, d.f.=7; 2013: t=-2.53, P=0.045, d.f.=6).
10 Over the whole four year period significantly fewer (t=-4.75; P<0.001; d.f.=41)
11 individuals occurred in all the grazed arrays (mean=2.1; SD=1.29; n=16) compared to all the
12 ungrazed arrays (mean=4.8; SD=2.55; n=28) and the overall total number of smooth snake
13 captures was also significantly lower (t=-3.56; P=0.001; d.f.=32) in grazed arrays (mean=4.25;
14 SD=3.21; n=16) than ungrazed arrays (mean=13.07; SD=12.41; n=28).
15
16 Smooth snake associations with heathland plant species
17 The data provided in Table 1 was used to select five plant species/assemblages, denoted with
18 an ‘*’ (heather: live C. vulgaris, E. cinerea, E. tetralix; U. minor; A. curtisii; M. caerulea and
19 moss), with which to investigate smooth snake occurrence. This selection was based on their
20 perceived ability to provide cover for smooth snakes and structure to the overall habitat (a
21 combination of tall plant height and high maximum % cover) and, in the case of moss, its
22 presence within most arrays and to varying depths. Tree saplings, plant species that did not
23 occur in both grazed and ungrazed areas, species providing a mean ground cover below five
24 percent or those with a mean height below five cm were excluded from further analysis.
9
1 The number of smooth snakes occurring within any array was defined both in terms of
2 the total number of individuals, and the total number of captures of all individuals, as any single
3 array may have had one resident smooth snake that was captured many times or a number of
4 ‘transient’ individuals that were each captured once or rarely. The total number of individual
5 smooth snakes and the total number of smooth snake captures recorded in each array during
6 each of the four years (2010-2013) were plotted against the mean height and percent cover of
7 the plant species within each array (Fig. 2). No smooth snakes were found in the burnt array.
8
9 Heather (C. vulgaris + E. cinerea + E. tetralix)
10 Fewer individuals and total captures were recorded from grazed arrays than from ungrazed
11 arrays. Most individuals and captures occurred in arrays with a mean heather height of 35-
12 40cm and the fewest in arrays with a mean heather height lower than about 25cm or greater
13 than approximately 50cm (Fig. 2). Where both grazed and ungrazed arrays had heather of a
14 similar mean height, or percentage cover, fewer snakes occurred in the grazed arrays than the
15 ungrazed arrays. The highest number of smooth snake individuals and captures were recorded
16 from ungrazed dry (Cv-Um) heath and the lowest from grazed wet (Um-Ac) heath. There were
17 significant positive relationships between the percent cover of heather and the total number of
18 smooth snake individuals (Ca Individuals = 0.783 + 0.096 %cover; r2=32.6%; P<0.001; n=48)
19 and captures (Ca Captures = -2.431 + 0.408 %cover; r2=35.4%; P<0.001; n=48).
20
21 Dwarf gorse (U. minor)
22 The total number of smooth snake individuals and captures were highest in dwarf gorse with a
23 height of approximately 25cm with fewest individuals or captures occurring in gorse with a
24 height below 13cm or above 35cm (Fig. 2). In arrays where gorse heights and percentage cover
25 were similar fewer snakes were recorded in grazed arrays than ungrazed arrays. However, in
10
1 Fig. 2. Plots of the total number of smooth snake individuals and total captures against mean
2 plant height/depth (a, b) and percent cover (c, d) for each refuge array located in dry (circles)
3 and wet (squares) heath within the grazed (●, ■) and ungrazed (○, □) areas (2010-2013).
4 Heather: C. vulgaris + E. cinerea + E. tetralix; Um: U. minor; Ac: A. curtisii; Mc: M. caerulea.
s 12 s 12 l a l c a 10 a 10
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T T 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 Mean Heather height - cm Mean % Heather cover
60 60 s b s d e 50 e 50
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T 0 T 0 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 Mean Heather height - cm Mean % Heather cover
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T 0 0 10 20 30 40 0 5 10 15 20 25 Mean Um height - cm Mean % Um cover
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1 Fig. 2. Cont’d
s 12 s 12 l a l c a 10 a 10
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T T 0 5 10 15 20 25 30 0 5 10 15 20 25 Mean Ac height - cm Mean % Ac cover
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T 0 T 0 0 5 10 15 20 25 30 0 5 10 15 20 25 Mean Ac height - cm Mean % Ac cover
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T T 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 Mean Mc height - cm Mean % Mc cover
60 60 s b s d e 50 e 50
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T 0 T 0 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 Mean Mc height - cm Mean % Mc cover
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1 Fig. 2. Cont’d
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T T 0 5 10 15 20 25 0 20 40 60 80 100 Mean moss height - cm Mean % Moss cover
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T 0 T 0 0 5 10 15 20 25 0 20 40 60 80 100 Mean moss height - cm Mean % Moss cover
2
3 contrast to heather, in arrays where gorse heights were similar the highest numbers of
4 individuals were recorded from ungrazed wet heath, rather than ungrazed dry heath, and the
5 lowest from grazed dry heath. There was no significant relationship between gorse cover and
6 either the total number of individuals (P>0.05) or captures (P>0.05).
7
8 Grasses (A. curtisii and M. caerulea)
9 The highest numbers of smooth snake individuals and captures were recorded from arrays on
10 wet heath where the mean heights of A. curtisii and M. caerulea were approximately 22cm and
11 35cm respectively (Fig. 2). The lowest numbers were found where the height of these two
12 species were below 7cm and 15cm or above 28cm and 53cm respectively. In arrays where grass
13 heights were similar the highest numbers of both individuals and captures were recorded in
14 ungrazed wet heath and the lowest in grazed dry heath. In arrays where the percentage cover
15 of A. curtisii and M. caerulea were similar the highest numbers of individuals and captures
13
1 occurred in ungrazed dry heath with relatively low grass cover (<5%) and the lowest in grazed
2 wet heath. There were no significant relationships between grass cover and either the total
3 number of individuals (P>0.05) or captures (P>0.05).
4
5 Moss
6 The mean depth and percent cover of moss were similar in both grazed and ungrazed arrays
7 (Fig. 2). However, as with heather, gorse and the grasses the total numbers of smooth snake
8 individuals and captures were lower in the grazed arrays than the ungrazed arrays. There was
9 no significant relationship between moss cover and either the total number of individuals
10 (P>0.05) or captures (P>0.05).
11
12 DISCUSSION
13 This study reports the observed annual changes in smooth snake C. austriaca numbers in an
14 area of wet and dry lowland heath that had been grazed annually for 13 years (1997-2009)
15 before cattle were excluded from part of it in 2010.
16 Prior to the exclusion of cattle from part of the study area in 2010, the patterns of change
17 in the number of smooth snake individuals recorded from both subsets of arrays were similar
18 with the observed decline in numbers, from about 2000, suggesting a possible delayed response
19 to the introduction of grazing in 1997. However, these declines may have been coincidental
20 with the introduction of grazing as similar declines were reported for a number of other snake
21 species from around the world, over the same period, where the cause was unknown though
22 habitat quality deterioration/change is suggested as one possibility (Gardner et al., 2007;
23 Reading et al., 2010).
24 The divergent trends in the mean number of smooth snake individuals occurring in the
25 subsequently grazed and ungrazed arrays following the cessation of grazing in 2010 support
14
1 the argument for grazing being the likely causal agent of the observed declines. Our data also
2 agree with the results of two studies of reptiles on heathland in The Netherlands where either
3 fewer reptiles were found in grazed heathland than ungrazed heathland (Strijbosch, 2002;
4 Stumpel & van der Werf, 2012) or they totally disappeared from grazed areas e.g. smooth snake
5 C. austriaca, common lizard Z. vivipara and slow worm A. fragilis (Strijbosch, 2002).
6 One possible explanation for the observed differences in smooth snake occurrence,
7 between the grazed and ungrazed areas (2010-2013), were changes to habitat structure, that
8 occurred over the same period, and the observed association of smooth snakes with particular
9 plant species and habitat attributes (plant height and percentage ground cover). Smooth snakes
10 are stated to prefer a well-structured habitat comprised predominantly of mature heather C.
11 vulgaris and M. caerulea with a deep litter layer of bryophytes (Braithwaite et al., 1989;
12 Corbett, 1990; Edgar et al., 2010). Our results support these assertions. Smooth snakes
13 occurred most frequently in ungrazed dry heath with a mean heather height of 35-45 cm and
14 the highest heather ground cover.
15 Cattle are known to graze heather C. vulgaris (Putman et al., 1987) and although it is
16 capable of vegetative regeneration, following light grazing, this ability declines with age.
17 Heavy grazing, or continued light grazing, also removes a substantial proportion of the foliage-
18 bearing shoots (Mohamed & Gimingham, 1970) and substantially reduces the litter layer
19 (Hancock et al., 2010). In addition, mature heather is also more vulnerable to trampling than
20 young heather (Corbett, 1990) such that the overall impact of cattle grazing is to reduce its
21 vertical structure (Newton et al., 2009).
22 The most noticeable differences between the grazed and ungrazed areas were in the
23 height and ground cover of M. caerulea, which in the grazed area were both less than half that
24 of the ungrazed area and which had clearly been cropped by cattle. The highest numbers of
25 smooth snake individuals, and captures, were associated with tall grass which was virtually
15
1 absent from the grazed areas as was grass litter. A critical prey species for juvenile smooth
2 snakes is Z. vivipara (Reading & Jofré, 2013), which prefers areas with a high cover of
3 relatively tall M. caerulea (Strijbosch, 1988; Edgar et al., 2010; Stumpel & van der Werf, 2012)
4 and for which grazing has been shown to have significant negative effects (Wallis de Vries et
5 al., 2013). The relatively low ground cover of short M. caerulea in the grazed area is therefore
6 unlikely to provide either sufficient protective cover or potential prey, particularly for juvenile
7 smooth snakes. In addition, major dietary components of adult smooth snakes are adult
8 common and pigmy shrews (Sorex araneus and S. minutus) and nestling small mammals,
9 particularly wood mice Apodemus sylvaticus and field voles Microtus agrestis (Reading &
10 Jofré, 2013) which are also negatively affected by grazing (Tubbs, 1997; Offer et al., 2003).
11 Along with habitat degradation, disturbance was considered to be an important threat
12 to the survival of local smooth snake populations in the southern Iberian Peninsula (Santos et
13 al., 2009) and may explain the lower number of smooth snake individuals and captures
14 recorded in the grazed area in our study. This possibility is supported by our finding that where
15 the vegetation height and/or percentage ground cover were similar in both grazed and ungrazed
16 arrays the number of smooth snake individuals and/or captures were almost always lower in
17 the grazed arrays.
18 The cattle stocking densities used in the study area were consistent with those
19 recommended by Lake et al. (2001). However, the total number of cows used in habitat
20 management employing ‘conservation grazing’ is based on the size of the area to be managed
21 and assumes that cattle will be evenly dispersed over all of it. If cattle avoid some areas (e.g.
22 bogs) then the true size of the area grazed will be smaller resulting in an underestimate of
23 stocking density. Similarly, the herding behaviour of cows also results in higher than
24 anticipated densities on those areas where they do roam, graze and rest by at least two orders
25 of magnitude, resulting in overgrazing e.g. cows introduced onto an area at an overall stocking
16
1 density of 0.2 cows/ha that then form groups of 20 individuals that occupy less than one hectare
2 when grazing, roaming or resting.
3 Our results suggest that cattle grazing has resulted in a slow degradation of the
4 heathland habitat structure within the study area, reducing its carrying capacity with respect to
5 smooth snakes and that its recovery, following the cessation of grazing, is also likely to be slow
6 (Lindenmayer & Fischer, 2006). Although M. caerulea is an important species in providing
7 part of the habitat structure on heathland, and recovers quickly once cattle grazing is removed,
8 the major structural component is provided by heather, mainly C. vulgaris, which has a
9 relatively slow annual growth rate resulting in a much longer recovery time.
10 Important questions that result from this study are what exactly is meant by
11 ‘conservation grazing’ and what, precisely, is it aiming to conserve? In the UK, Natural
12 England states that its policy of using grazing on heathland is designed to ‘conserve wildlife
13 and maintain biodiversity’ (see NEa) despite numerous studies, worldwide, demonstrating that
14 with the exception of a few species that are adapted to early successional stages (Kie et al.,
15 1996; Buckley, Beebee & Schmidt, 2013), grazing is usually damaging to species that require
16 a habitat with high structural complexity (Lindenmayer & Fischer, 2006; Jofré & Reading,
17 2012). The crux of the problem is that every species requiring conservation has its own unique
18 set of habitat requirements and that the policy of using grazing as a ‘one-size-fits-all’ solution
19 for their conservation is a nonsense.
20 There is an increasing need for those bodies charged with conserving the natural
21 environment to make potentially difficult decisions about which species within given habitats,
22 or parts of habitats, should be targeted for conservation measures. It is, therefore, almost
23 inevitable that more than one conservation management protocol will be required within any
24 given habitat to address the specific habitat requirements of each species considered to be at
17
1 risk. It is also extremely important that the areas managed for each target species should be
2 sufficiently large to support sustainable populations.
3 Regrettably, ‘conservation grazing’, particularly of heathland, is a management tool
4 that works at the landscape level (Stumpel & van der Werf, 2012) when the real problem lies
5 at the species habitat level (Lake et al., 2001) and at this level, the specific habitat requirements
6 of many species, which may vary with life stage, remain largely unknown. There is, therefore,
7 an urgent need for research into the specific habitat requirements of threatened species before
8 the implementation of untested and untargeted management protocols to conserve them,
9 followed by detailed monitoring to determine their real, as opposed to anticipated, impact
10 (Bullock & Pakeman, 1997; Newton et al., 2009; Böhm et al., 2013).
11
12 ACKNOWLEDGEMENTS
13 We wish thank M. Warn, the Forestry Commission Wildlife Ranger for Wareham Forest, for
14 allowing us unhindered access to Wareham Forest at all times. Thanks also to the Forestry
15 Commission and Natural England who jointly funded the erection of the cattle exclusion fence
16 and to the graziers for annual stocking densities. The research on smooth snakes was completed
17 under licence from Natural England, UK.
18
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