Biodiversity and Conservation (2005) 14: 1969–1976
DOI 10.1007/s10531-004-2125-6
Ó Springer 2005
-1
Agri-environment schemes and butterflies: the
utilisation of 6 m grass margins
R.G. FIELD1,*, T. GARDINER1, C.F. MASON2 and J. HILL3
1
Centre for Environment and Rural Affairs, Writtle College, Writtle, Chelmsford, Essex CM1 3RR,
UK; 2Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4
3SQ, UK; 3Department of Science, Writtle College, Writtle, Chelmsford, Essex CM1 3RR, UK;
*Author for correspondence (e-mail: [email protected]; rfi[email protected])
Received 10 October 2003; accepted in revised form 23 February 2004
Key words: Agri-environment schemes, Butterflies, Countryside Stewardship Scheme, Field margins, Grassland
Abstract. The utilisation of 6 m countryside stewardship scheme (CSS) grass margins by butterflies
was studied at two farms in Essex between 1997 and 2000. The aim of the study was to establish
whether grass margins in cereal fields, as set up and managed under CSS guidelines, would be
beneficial to common farmland butterflies. Eight 6 m grass margins (total length 3492 m) and two
control sections (no margin; total length 700 m) were monitored over the first years of the agreements using the transect method. Significantly greater total numbers of butterflies and individuals
of Maniola jurtina were seen on the 6 m grass margins than on the control sections. There was a
significant increase in abundance of Maniola jurtina on the margins over the 4-year study period.
Significantly more butterflies and Maniola jurtina were seen on the sown 6 m grass margin next to
set-aside than on any of the other methods of establishment. Sown next to set-aside was best for
Pyronia tithonus, but not significant.
Introduction
Since the 1940s the landscape of the UK has been dramatically transformed by
the intensification of arable systems (Dover 1997). One of the major changes is
the loss of grassland, with 40% of lowland heath, 97% of lowland flower-rich
grassland and 80% of chalk and limestone grassland disappearing (Asher et al.
2001), and the reduction in suitable habitat has had a marked effect on
butterflies. These types of grassland support between 19 and 28 species of
butterflies, while improved grassland only supports one to three butterfly
species (Thomas 1984). Overall, butterfly distribution and abundance has declined over the last 150 years (Heath et al. 1984; Thomas 1984; Asher et al.
2001), but this reduction is due not only to changes in farming practices, but
also to other factors such as climate change (Warren et al. 1997).
Cereal field margins are one of the UK habitats subject to a biodiversity
action plan (BAP). Agri-environmental schemes, such as the countryside
stewardship scheme (CSS) in England are seen as a key mechanism by which
BAP targets may be met (Smallshire and Cooke 1999). The introduction of
1970
these schemes began to move payments away from production based
agriculture to more environmentally sensitive farming. One part of the CSS
was the introduction of 6 m grass margins around arable fields, to provide
wildlife habitats, wildlife corridors and to buffer field boundaries, streams and
rivers from agricultural operations.
The objectives of this study were to investigate whether CSS 6 m grass
margins would provide suitable butterfly habitats, and to monitor the effects
on butterfly abundance over the first 4 years of the agreements.
Material and methods
Study sites and management
Two arable farms in Essex, southeast England, were studied. They were Writtle
College farm, Chelmsford (NGR: TL670070) and Greenstead Green farm,
Halstead (NGR: TL810280). Both applied to join the CSS on October 1st,
1996, and entered into the scheme with 2380 and 2920 m respectively of 6 m
arable margins.
In the first year grass margins should be cut three times before September
and in subsequent years cut after July 15th, with all cuttings removed. The
specification was that seed should be sown at 20 kg/ha and should contain at
least four species of grass from a list provided, no one species making up more
than 40% of the seed mix. The CSS agreement states that the seed should be
from a native source where possible, but agriculturally improved cultivars were
used at all sites. There was no requirement to use any wildflower seed within
the mixtures. Alternatively the margins could be established using natural
regeneration. Eight sections of 6 m arable margins were investigated. Three
margins at Writtle were established using natural regeneration, while four
margins at Greenstead Green and one at Writtle were established by sowing a
range of grasses. The seed mixture used at Greenstead Green consisted of six
species: Cynosurus cristatus, Festuca ovina, Agrostis capillaris, Festuca rubra,
Festuca rubra subsp. commutata and Poa pratensis. At Writtle nine species were
sown: Cynosurus cristatus, Festuca ovina, Agrostis capillaris (two cultivars),
Festuca pratensis, Festuca rubra subsp. commutata, Festuca arundinacea,
Dactylis glomerata, and Alopecurus pratensis.
In this study 2242 m at Writtle (mean 560.5 m, range 190–720 m) and
1250 m at Greenstead Green (mean 312.5 m, range 166–417 m) of 6 m grass
margins were monitored for butterflies. This included all 6 m margins which
could be sensibly monitored without wasting time walking from one end of
the farm to the other. Both sites had a control section, Writtle 450 m and
Greenstead Green 250 m, which was an arable field edge with no margin.
These were the maximum lengths left without margins at each site. The grass
margins were managed as outlined in the CSS regulations for the 4 years of
the study period. The vegetation growing on the 6 m grass margins was
1971
monitored each year in July, after the first set up year. All species on every
grass margin were identified and then given a classificiation using the DAFOR
scale (Bullock 1996).
On the sown 6 m grass margins at Greenstead Green, of the six species in the
original mix, two species were not recorded as being present by 2000 and one
other species was only found rarely in one margin, the most common species
being Cynosurus cristatus and Festuca rubra subsp. commutata. At Writtle, the
most abundant species by 2000 in the sown margin were Dactylis glomerata
and Festuca arundinacea, with Festuca ovina and Festuca pratensis no longer
being recorded.
The margins at Writtle, which had been established by natural regeneration,
were developed in two different ways, the first being from a prepared seed bed
left to develop naturally. By 2000 this had developed into an open sward with
Poa trivialis, Elytrigia repens, Arrhenatherum elatius, Anisantha sterilis, and
Cirsium arvense being abundant. The second method used was to leave a 6 m
strip unploughed after a field had been a grass ley within the arable rotation.
The grass mix used to establish this ley had been Lolium multiflorum and
Lolium perenne. These two species persisted and by 2000 were still abundant
within the margin. Suitable butterfly nectar sources were not included in any of
the original mixtures and few, if any, were recorded in the margins or control
sections within the first 4 years.
Butterfly monitoring
All butterflies observed on the field margins were recorded but special note was
taken of the ‘key’ species which all use grasses in their larval stage: Maniola
jurtina (L.), Pyronia tithonus (L.), Thymelicus sylvestris (Poda), Thymelicus
lineola (Ochs.) and Ochlodes venata (B. & G.). All these grassland species are
considered to form ‘closed’ populations (Thomas 1984) and are relatively
sedentary and breed widely in field margins, so should benefit from the
establishment of grassland habitats around arable farmland. Due to difficulties
in identification Thymelicus sylvestris and Thymelicus lineola were counted
together (Pollard and Yates 1993) and will hereafter be referred to as
Thymelicus spp.
The research and control sections were monitored weekly during the period
late June to early August 1997–2000. The walks took place when the weather
conditions met the required criteria (Pollard 1977). Thus seven counts were
undertaken in 1997, five in 1998, six in 1999 and four in 2000. All butterflies
seen on the 6 m grass margins, hedgerows and hedge–margin interface were
recorded using the standard butterfly monitoring scheme (BMS) method
(Pollard and Yates 1993). The two sites had a transect which was walked every
week during the research period (Pollard and Yates 1993).
Non-parametric tests were used to analyse the data collected. The Mann–
Whitney U-test was used to compare two samples (unmatched samples). The
1972
Kruskal–Wallis test with Dunn’s Multiple Comparison (Dunn 1964) was used
to compare more than two samples.
Results
Butterfly abundance was significantly higher on the 6 m grass margins than on
the control sections (U = 4.5, p < 0.001) but butterfly species richness was
higher on the control sections (Table 1). A total of 19 common species were
observed on the 6 m grass margins and 12 species on the control sections. The
non-key species made up 40% of the observed butterflies on the 6 m grass
margins but only made up 26% on the control sections. There was significantly
greater abundance of butterflies observed on the 6 m grass margins at
Greenstead Green than at Writtle (U = 39, p < 0.01) (Table 2). There was no
significant difference between the abundance of butterflies seen on the transects
over the years 1997–2000 or between sites.
The abundance of Maniola jurtina was significantly greater on the 6 m grass
margins than on the control sections (U = 49, p < 0.05; Table 1). There was a
significant increase in abundance of Maniola jurtina over the research period
(U = 2, p < 0.05; Table 3). There was no significant difference between the
abundance of Pyronia tithonus, Thymelicus spp., and Ochlodes venata on the
6 m grass margins and the control sections (Table 1), nor was there any
significant change in abundance between 1997 and 2000 (Table 3).
Table 1. Number of butterflies [butterflies per km per visit (b/km/v)] seen on the 6 m grass
margins 1997–2000.
Butterflies
Six metre margins mean (range)
Control mean (range)
Significance
All
Species richness
Maniola jurtina
Pyronia tithonus
Thymelicus spp.
Ochlodes venata
45.8
8.1
18.9
5.1
3.3
0.3
20.9
8.9
4.9
7.3
2.3
0.9
***
ns
*
ns
ns
ns
(8.8–195.4)
(4–13)
(0–91.4)
(0–58.7)
(0–13.7)
(0–1.1)
(9.0–41.0)
(4–11)
(0–10.4)
(0–21.1)
(0–6.7)
(0–2.5)
Mann–Whitney U-test: ***p < 0.001; *p < 0.05; ns, not significant.
Table 2. Number of butterflies (b/km/v) seen on the 6 m grass margins at the study sites.
Butterflies
Writtle mean (range)
Greenstead Green mean (range)
Significance
All
Maniola jurtina
Pyronia tithonus
Thymelicus spp.
Ochlodes venata
32.1
4.1
3.6
3.5
0.4
59.4
33.7
6.4
1.9
0.2
**
**
ns
ns
ns
(8.8–62.4)
(0–11.7)
(0–18.2)
(0.6–13.7)
(0–2.2)
(18.8–195.4)
(3.2–91.4)
(0–58.7)
(0–8.7)
(0–1.2)
Mann–Whitney U-test: **p < 0.01; ns, not significant.
1973
Table 3. Number of butterflies (b/km/v) seen per year on 6 m grass margins.
Butterflies
1997 Mean
(range)
1998 Mean
(range)
1999 Mean
(range)
2000 Mean
(range)
All
25.6 (15.0–50.0) 46.4 (36.8–68.8) 53.4 (8.8–111.2) 57.8 (18.0–195.4)
Maniola
2.3 (0–3.7)
9.5 (0.8–23.2) 35.0 (1.0–91.0) 28.9 (1.3–87.0)
jurtina
Pyronia
1.1 (0–4.3)
1.3 (1.1–8.2)
6.3 (1.6–18.2) 11.2 (0.7–58.7)
tithonus
Thymelicus 1.1 (0–4.2)
4.6 (0–13.7)
3.2 (0–7.8)
4.1 (0.6–8.7)
spp.
Ochlodes
0.5 (0–1.0)
0.2 (0–0.6)
0.4 (0–0.6)
0.1 (0–1.1)
venata
Significance
97 versus 00
ns
+*
ns
ns
ns
Mann–Whitney U-test: *p < 0.05; ns, not significant; +, significant increase.
Table 4. Butterflies (b/km/v) observed on 6 m grass margins established using different techniques
1997–2000.
Butterflies
Sown n = 4
Natural
regeneration
n=2
From ley
n=1
Sown next
to set-aside
n=1
All
40.9a (8.8–73.0) 31.6a (1.5–62.4) 38.0a (18.0–50.0) 125.1b (68.8–195.4)
Maniola
26.6b (0.9–91.4) 4.1a (0–8.3)
5.3a (0.8–15.0)
56.8c (23.2–89.3)
jurtina
Pyronia
2.9 (0–9.0)
4.4 (0–18.2)
3.4 (0.7–4.7)
23.0 (2.2–58.7)
tithonus
Thymelicus 3.1 (0–12.6)
3.3 (0.6–5.7)
6.4 (1.7–11.1)
4.2 (0–8.7)
spp.
Ochlodes
0.1 (0–1.0)
0.4 (0–1.1)
0.7 (0–2.4)
0.3 (0–1.0)
venata
Significance
*
**
ns
ns
ns
Means on the same row followed by a different superscript letter are significantly different. Dunn’s
Procedure (Dunn 1964): **p < 0.01, *p < 0.05, ns, not significant. n, number of replicates per
type.
When butterfly abundance for the different types of establishment methods
was compared with a sown grass margin next to a field in permanent setaside, a range of results were obtained (Table 4). Significantly more butterflies (H = 8.48, p < 0.05) and Maniola jurtina (H = 12.45, p < 0.01) were
observed on the 6 m grass margin established next to the set-aside field than
on any of the other margins. Natural regeneration was the worst option for
all butterflies and for Maniola jurtina. Sown (not next to set-aside) was the
worst option for Pyronia tithonus, Thymelicus spp., and Ochlodes venata and
margins developed from a ley were best for Thymelicus spp., and Ochlodes
venata.
By 2000 there was a significant relationship between the length of hedgerow
and the number of plant species found in the margins (rs = 0.8, p < 0.05).
1974
Discussion
The concept that all 6 m CSS grass margins would be beneficial to a range of
grassland butterflies must be questioned, especially during the first 4 years. A
significantly greater abundance of all butterflies and Maniola jurtina were
found on the 6 m grass margins than on the control section. However, except
for Maniola jurtina there was no significant increase in butterfly abundance
over the research period. Other species such as Pyronia tithonus and Ochlodes
venata faired better on control sections than on the 6 m grass margins. There
were significant differences in butterfly abundance depending on the method
used to establish the margins and their position, and a significant difference in
abundance at the two sites.
Clausen et al. (2001) observed that there was a relationship between butterfly
abundance in non-linear and linear habitats. The ratio observed for Maniola
jurtina in that study was 4.9:1. The sown margin next to the set-aside in this
study could be classed as a non-linear habitat, while 6 m grass margins are
linear habitats. The observed ratio in 2000 was 4.7:1 for Maniola jurtina and
3.4:1 for all butterflies when comparing the 6 m grass margin next to set-aside
to all the other 6 m grass margins.
Natural regeneration as a method for establishing margins on clay soils was
not recommended by Marshall (1998), and in fact it turned out to be the worst
option in this study for all butterflies and Maniola jurtina. It was also unacceptable to the farm enterprise due to the wide range of arable weeds which it
supported. The sown margins were all established using imported seed mixtures, comprising agriculturally improved cultivars of grasses. Seed was bought
solely on price and contained three species at Writtle and two at Greenstead
Green which were not suitable for the soil type (Marshall 1998).
Within the first 4 years none of the margins had enough nectar sources
within them for butterflies to use. The best predictors of Maniola jurtina, Pyronia tithonus, and Thymelicus spp. abundance identified by Feber et al. (1996)
were nectar sources such as Leucanthemum vulgare, Centaurea spp., and
Knautia arvensis. These were all absent from every 6 m grass margin within the
two sites.
The management of the 6 m grass margins was not suitable for Thymelicus
spp., both of which are vulnerable to cutting of vegetation (Brakefield et al.
1992). If the 6 m grass margins were cut on or just after the date stated (15th
July) in the agreements most, if not all, of the eggs of both species, plus all the
nectar sources for Maniola jurtina and Pyronia tithonus would be removed.
Smith et al. (1993) suggested that summer cutting reduced butterfly abundance
by over 50%, when compared to an early spring cut followed by a second cut in
autumn.
Other associated difficulties with 6 m grass margins included lack of habitat
size. None of the margins met the minimum size required by butterflies
(Thomas 1984), while the height of the sward was also too tall for nearly all the
grassland butterflies (Goldsmith 1991). Many other studies have identified
1975
similar problems with a lack of nectar sources being critical to butterfly survival (Watt et al. 1974; Murphy et al. 1983; Dover 1994; Feber et al. 1996;
Dover 1999) with grass only strips being poorest for butterfly abundance (Buys
1995; de Leeuw et al. 1995; Buys et al. 1996; Carreck et al. 1999).
Conclusions
The utility of 6 m grass margins under the CSS scheme for butterflies must be
questioned. The lack of nectar sources, the use of agricultural cultivars of
grasses, the size and position of the margins and their management did not
benefit the abundance of common butterflies on farmland in this study. Butterfly populations may be enhanced when some of these problems are remedied. The findings at Greenstead Green suggest that margins positioned
adjacent to set-aside may be the most beneficial for butterflies.
With respect to butterflies the current CSS prescriptions could be improved
to produce better quality grass and wildflower margins sited in more beneficial
positions. One option would be to provide more guidance for the farmer and
pay more to create and manage better wildlife habitats, beyond simply providing improved grass margins which is the current practice.
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