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The effects of woodland management for pheasants on the abundance of butterflies in Dorset, England
Biological Conservation 45 (1988) 159-167
The Effects of Woodland Management for Pheasants on the Abundance of Butterflies in Dorset, England
P. A. R o b e r t s o n , a* M. I. A. W o o d b u r n b & D. A. Hill a a The Pheasants and Woodlands Project, The Game Conservancy Trust, Fordingbridge, Hampshire, SP6 1EF, UK h Centre for Environmental Technology, Imperial College, London SW7, UK (Received 27 September 1986; revised version received 24 October 1986; accepted 9 March 1988)
ABSTRACT A survey of butterfly numbers was conducted on an area of woodland in Southern England using the transect method described by E. Pollard (1977), Biol. Conserv., 12, 115-24. The woodland contained areas of commercial forestry, areas managed specifically for pheasants, and unmanaged areas of derelict hazel coppice. Butterfly numbers were compared between these types. Areas managed for pheasants contained significantly higher numbers and more species of butterflies than commercial or unmanaged areas. This appeared to be due to the wider width of the rides and more open canopy in woodland managed for pheasants, which allowed light to penetrate and encouraged the growth of ground flora, an effect known to be beneficial for both pheasants and butterflies. Woodland management for pheasants can benefit many of the declining butterfly species associated with sunny, open woods. We suggest that the benefits for shooting may provide the incentive for landowners to carry out woodland management. * To whom correspondence should be addressed. 159 BioL Conserv. 0006-3207/88/$03-50 © 1988 Elsevier Applied Science Publishers Ltd, England. Printed in Great Britain
160
P. A. Robertson, M. L A. Woodburn, D. A. Hill
INTRODUCTION At the turn of the century almost 30% of the 17 500ha of woodland in Dorset was coppiced and provided suitable conditions for many of the butterflies associated with the early stages of woodland succession. Although the area of woodland has recently increased to around 23 000 ha, mainly due to the planting of conifers, open or coppiced woodlands now comprise less than 2% of the total (Warren, 1976). The remaining areas of broadleaved woodlands are typically unmanaged and often derelict. They have not only lost most of their value as areas of commercial timber production but have also greatly decreased in importance as habitats for many species of wildlife. This loss of managed woodland has been thought to be responsible for the declines in many of our woodland species of butterflies (Heath et al., 1984; Thomas & Webb, 1984). The picture is the same across much of the country. The Forestry Commission estimates that a significant proportion of the 329 000 ha of high forest and 231 000ha of coppice mixed with standards or scrub in England and Wales are currently unmanaged. Pheasant management is one factor acting to promote woodland conservation. Shoard (1980) and Cobham Resource Consultants (1983) state that game conservation is directly responsible for many landowners retaining, planting and managing their broadleaved woodlands. Furthermore, the sporting revenue generated by a well-designed pheasant wood can often exceed that of the timber. Also, pheasant shooting can be an important incentive for landowners to begin managing existing woodlands. Woodland management for pheasants can take many forms (Gray, 1986), two of the most common being to thin trees out to allow the growth of ground flora and the widening of existing rides to provide stands for gun positions on shooting days. Pheasants are known to actively select areas of woodland with an appreciable growth of ground flora (Robertson, 1985, 1986), while coppiced woodland can provide some of the best habitats for this gamebird (Hill & Edwards, 1986). These latter authors also assert that game interests have maintained many areas of coppice that would otherwise be uneconomical. Pheasant shooting can create the incentive for landowners to conduct active woodland management, and this paper aims to investigate the little known effects of such management on butterfly numbers.
METHODS Counts of butterflies were made on a wooded area of the Wimborne St Giles Estate, in South East Dorset (Fig. 1) on six occasions at approximately ten-
Pheasant woodland management and butterflies
161
Pheasant rides
plantations
500m I
I
Broadleaved plantations
F
Fig. 1. A map of the study area near Wimborne St Giles, Dorset, showing the position of different woodland types. Transect routes shown in white. Pheasant rides, Q; open woodland, El; coniferous plantations, I ; broadleaved plantations, II. day intervals during July and August 1986. A series of twenty-six 2 0 0 m transects were walked on each day and the n u m b e r s of butterflies seen in a 5 m 2 box in front of the observer were recorded following the method described by Pollard (1977) and Hall (1981). These transects were designed to include a variety of w o o d l a n d types, edges and rides, some of which had been specifically managed for pheasants. C o u n t s were conducted between 10 00 h and 16 00 h on sunny days. To examine the distribution o f butterflies within the woodland, the transects were divided into five categories:
162 (i)
(ii)
(iii) (iv) (v)
P. A. Robertson, M. L A. Woodburn, D. A. Hill
Pheasant rides; clearings within the woodland, created and managed specifically to provide areas in which to position the guns during pheasant shoots. Typically, they were 30-50m in width and 100-150 m in length. The open areas thus created were cleared of scrub every three years. Open woodland; mixed coniferous and deciduous woodland with an open canopy, predominantly of oak and larch standards, with an appreciable growth of ground cover, mainly bracken, bramble and bluebell with coppiced hazel in places. Approximately half of these areas had been created specifically for pheasants. Woodland-field edges; the boundaries of deciduous woodland and pasture or cereal fields. Coniferous plantations; commercial areas of coniferous forestry which typically lacked any ground cover whatsoever. Unmanaged broadleaved woodland; areas ofbroadleaved woodland with a closed canopy, including areas of oak standards over old, unmanaged hazel coppice, with little or no ground cover.
RESULTS A total of 844.butterflies of 21 different species were observed during the study period. Significantly more were seen in those areas of woodland that had been managed for pheasants (n = 673, 46-7 k m - 1) compared to the other woodland areas (n = 42, 3"5 k m - 1) (X2 = 453.4, df = 1, p < 0.001). The numbers of each species seen in each habitat type and the corresponding numbers per km are presented in Table 1. The pheasant rides contained the highest numbers of 17 out of the 21 species seen, the exceptions being marbled whites Melanargia galathea, speckled woods Pararge aegeria, painted ladies Cynthia cardui and green-veined whites Pieris napi. The latter two species were only seen on single transects in any case. These rides also contained the highest number of species of any habitat types under consideration. Woodlands with an open canopy contained more individuals than closed canopy coniferous plantations and unmanaged broadleaved areas. All the transects, with the exception of those along woodland field edges, which are excluded from the following calculations, followed tracks or paths of some sort through the woodlands. The width of any gaps in the canopies above each path or track was estimated to the nearest 5 m at 10 m intervals. The relationship between path width and the total number of butterflies seen on that transect is presented in Fig. 2. Proportionally more butterflies were observed on transects along paths with wider gaps in their canopies than on
Pheasant woodland management and butterflies
163
200,
Total no.
butterflies
1OO •
y = 8-36+2.16x
C O*S O ~
0 Fig. 2.
30 Mean width of ~
60 in canopy (m)
The relationship between the mean width of gaps in the tree canopy and the total numbers of butterflies seen per transect.
transects along paths with narrow or no gaps in their canopies. The width of the gaps explained 45% of the observed variation in butterfly numbers between transects (r = 0.67, df = 20, p < 0.001). DISCUSSION The results of this study suggest that woodland management intended to benefit the holding capacity and shooting of pheasants in the winter can also provide better habitats for many of the woodland butterflies during the summer months. The most simple method of improving an area of unmanaged woodland for pheasants is to remove some of the standards to increase the penetration of light to the woodland floor. The resultant increase in the ground flora provides a preferred habitat for pheasants (Robertson, 1985, 1986) while an open canopy has been shown in this study a n d by Pollard (1982) and Warren (1985) to be an important factor influencing butterfly abundance. Only 2% of the woodlands in Dorset still provide the sunny open conditions that are essential for most of the traditional species of woodland butterflies, the remainder being shadier than at any time 'in the last thousand years or more' (Thomas & Webb, 1984). Many species of butterfly associated with such open woodland have declined during the latter half of this century,
164
P. A. Robertson, M. L A. Woodburn, D. A. Hill
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P. A. Robertson, M. I. A. Woodburn, D. A. Hill
while those more tolerant of shade, such as the white admiral Lagoda camilla and speckled wood, have increased. Indeed, Heath et al. (1984) state that the recent spread of the few species that require more shady conditions reinforces the belief that it is alterations in woodland structure that have been of paramount importance in determining changes in the status of these butterflies. The large rides created as stands for shooting attracted large numbers of butterflies in this study, including many grassland species as well as those associated with woodlands. In fact these rides contained higher densities of grassland species than did those woodland/field edges sampled. This may be due to their sheltered position as well as the absence of pesticides, which may reduce butterfly abundance in many agricultural habitats (Rands & Sotherton, 1986). A survey conducted by Cobham Resource Consultants (1983) states that of over 400 small woodland owners questioned as to their reasons for retaining and planting small woods, 67% and 56% respectively specified that game was one of the motives, placing it second only to landscaping, and above commercial timber production, shelter, fuel wood, wildlife conservation, screening, recreation and fox hunting. Many species of woodland butterflies are suffering from the decline in the area of managed broadleaved woodland. The value of woodlands for game is greatly appreciated by landowners while management for pheasants is also beneficial for many of the declining species of butterflies. The encouragement and education of landowners to manage their woodlands for pheasants may benefit butterflies and other species of wildlife associated with more open woodland habitats.
ACKNOWLEDGEMENTS Thanks are due to Lord Shaftsbury for permission to work on his estate; to Dick Potts, Nick Sotherton and John Dover for commenting on earlier drafts and to Don Ford and Phillipa Bond for their help.
REFERENCES Cobham Resource Consultants (1983). Countryside sports, their economic significance. The Standing Conference on Countryside Sports, Reading. Gray, N. (1986). Woodland management for pheasants and wildlife. David and Charles, London, p. 176. Hall, M. (1981). The butterfly monitoring scheme. Institute of Terrestrial Ecology, Huntingdon.
Pheasant woodland management and butterflies
167
Heath, J., Pollard, E. & Thomas, J. A. (1984). Atlas of butterflies in Britain and Ireland. Viking, Harmondsworth, p. 158. Hill, D. A. & Edwards, J. (1986). The compatibility of pheasant management and woodland conservation with emphasis on Southern English coppice. Paper presented at the Recreation Ecology Research Group meeting, Wye College, Kent, April 1986. Pollard, E. (1977). A method for assessing changes in the abundance of butterflies. BioL Conserv., 12, 115-24. Pollard, E. (1982). Monitoring butterfly abundance in relation to the management of a nature reserve. Biol. Conserv., 24, 317-28. Rands, M. R. W. & Sotherton, N. W. (1986). Pesticide use on cereal crops and changes in the abundance of butterflies on arable farmland in England. Biol. Conserv., 36, 71-82. Robertson, P. A. (1985). Habitat selection and the relative distributions of wild and released pheasants (Phasianus colchicus) as determined by winter trapping. J. Worm Pheasant Assoc., 10, 87-99. Robertson, P. A. (1986). The ecology and management of hand-reared and wild pheasants (Phasianus colchicus) in Ireland. PhD thesis, National University of Ireland. Shoard, M. (1980). The theft of the countryside. Temple Smith, London, p. 260. Thomas, J. & Webb, N. (1984). Butterflies of Dorset. Dorset Natural History and Archaeological Society, Dorchester, p. 128. Warren, M. S. (1976). The Dorset woodlands--their history and conservation. M Sc thesis, University College, London. Warren, M. S. (1985). The influence of shade on butterfly numbers in woodland rides, with special reference to the wood white Leptidea sinapis. Biol. Conserv., 33, 147-64.
The Effects of Woodland Management for Pheasants on the Abundance of Butterflies in Dorset, England
P. A. R o b e r t s o n , a* M. I. A. W o o d b u r n b & D. A. Hill a a The Pheasants and Woodlands Project, The Game Conservancy Trust, Fordingbridge, Hampshire, SP6 1EF, UK h Centre for Environmental Technology, Imperial College, London SW7, UK (Received 27 September 1986; revised version received 24 October 1986; accepted 9 March 1988)
ABSTRACT A survey of butterfly numbers was conducted on an area of woodland in Southern England using the transect method described by E. Pollard (1977), Biol. Conserv., 12, 115-24. The woodland contained areas of commercial forestry, areas managed specifically for pheasants, and unmanaged areas of derelict hazel coppice. Butterfly numbers were compared between these types. Areas managed for pheasants contained significantly higher numbers and more species of butterflies than commercial or unmanaged areas. This appeared to be due to the wider width of the rides and more open canopy in woodland managed for pheasants, which allowed light to penetrate and encouraged the growth of ground flora, an effect known to be beneficial for both pheasants and butterflies. Woodland management for pheasants can benefit many of the declining butterfly species associated with sunny, open woods. We suggest that the benefits for shooting may provide the incentive for landowners to carry out woodland management. * To whom correspondence should be addressed. 159 BioL Conserv. 0006-3207/88/$03-50 © 1988 Elsevier Applied Science Publishers Ltd, England. Printed in Great Britain
160
P. A. Robertson, M. L A. Woodburn, D. A. Hill
INTRODUCTION At the turn of the century almost 30% of the 17 500ha of woodland in Dorset was coppiced and provided suitable conditions for many of the butterflies associated with the early stages of woodland succession. Although the area of woodland has recently increased to around 23 000 ha, mainly due to the planting of conifers, open or coppiced woodlands now comprise less than 2% of the total (Warren, 1976). The remaining areas of broadleaved woodlands are typically unmanaged and often derelict. They have not only lost most of their value as areas of commercial timber production but have also greatly decreased in importance as habitats for many species of wildlife. This loss of managed woodland has been thought to be responsible for the declines in many of our woodland species of butterflies (Heath et al., 1984; Thomas & Webb, 1984). The picture is the same across much of the country. The Forestry Commission estimates that a significant proportion of the 329 000 ha of high forest and 231 000ha of coppice mixed with standards or scrub in England and Wales are currently unmanaged. Pheasant management is one factor acting to promote woodland conservation. Shoard (1980) and Cobham Resource Consultants (1983) state that game conservation is directly responsible for many landowners retaining, planting and managing their broadleaved woodlands. Furthermore, the sporting revenue generated by a well-designed pheasant wood can often exceed that of the timber. Also, pheasant shooting can be an important incentive for landowners to begin managing existing woodlands. Woodland management for pheasants can take many forms (Gray, 1986), two of the most common being to thin trees out to allow the growth of ground flora and the widening of existing rides to provide stands for gun positions on shooting days. Pheasants are known to actively select areas of woodland with an appreciable growth of ground flora (Robertson, 1985, 1986), while coppiced woodland can provide some of the best habitats for this gamebird (Hill & Edwards, 1986). These latter authors also assert that game interests have maintained many areas of coppice that would otherwise be uneconomical. Pheasant shooting can create the incentive for landowners to conduct active woodland management, and this paper aims to investigate the little known effects of such management on butterfly numbers.
METHODS Counts of butterflies were made on a wooded area of the Wimborne St Giles Estate, in South East Dorset (Fig. 1) on six occasions at approximately ten-
Pheasant woodland management and butterflies
161
Pheasant rides
plantations
500m I
I
Broadleaved plantations
F
Fig. 1. A map of the study area near Wimborne St Giles, Dorset, showing the position of different woodland types. Transect routes shown in white. Pheasant rides, Q; open woodland, El; coniferous plantations, I ; broadleaved plantations, II. day intervals during July and August 1986. A series of twenty-six 2 0 0 m transects were walked on each day and the n u m b e r s of butterflies seen in a 5 m 2 box in front of the observer were recorded following the method described by Pollard (1977) and Hall (1981). These transects were designed to include a variety of w o o d l a n d types, edges and rides, some of which had been specifically managed for pheasants. C o u n t s were conducted between 10 00 h and 16 00 h on sunny days. To examine the distribution o f butterflies within the woodland, the transects were divided into five categories:
162 (i)
(ii)
(iii) (iv) (v)
P. A. Robertson, M. L A. Woodburn, D. A. Hill
Pheasant rides; clearings within the woodland, created and managed specifically to provide areas in which to position the guns during pheasant shoots. Typically, they were 30-50m in width and 100-150 m in length. The open areas thus created were cleared of scrub every three years. Open woodland; mixed coniferous and deciduous woodland with an open canopy, predominantly of oak and larch standards, with an appreciable growth of ground cover, mainly bracken, bramble and bluebell with coppiced hazel in places. Approximately half of these areas had been created specifically for pheasants. Woodland-field edges; the boundaries of deciduous woodland and pasture or cereal fields. Coniferous plantations; commercial areas of coniferous forestry which typically lacked any ground cover whatsoever. Unmanaged broadleaved woodland; areas ofbroadleaved woodland with a closed canopy, including areas of oak standards over old, unmanaged hazel coppice, with little or no ground cover.
RESULTS A total of 844.butterflies of 21 different species were observed during the study period. Significantly more were seen in those areas of woodland that had been managed for pheasants (n = 673, 46-7 k m - 1) compared to the other woodland areas (n = 42, 3"5 k m - 1) (X2 = 453.4, df = 1, p < 0.001). The numbers of each species seen in each habitat type and the corresponding numbers per km are presented in Table 1. The pheasant rides contained the highest numbers of 17 out of the 21 species seen, the exceptions being marbled whites Melanargia galathea, speckled woods Pararge aegeria, painted ladies Cynthia cardui and green-veined whites Pieris napi. The latter two species were only seen on single transects in any case. These rides also contained the highest number of species of any habitat types under consideration. Woodlands with an open canopy contained more individuals than closed canopy coniferous plantations and unmanaged broadleaved areas. All the transects, with the exception of those along woodland field edges, which are excluded from the following calculations, followed tracks or paths of some sort through the woodlands. The width of any gaps in the canopies above each path or track was estimated to the nearest 5 m at 10 m intervals. The relationship between path width and the total number of butterflies seen on that transect is presented in Fig. 2. Proportionally more butterflies were observed on transects along paths with wider gaps in their canopies than on
Pheasant woodland management and butterflies
163
200,
Total no.
butterflies
1OO •
y = 8-36+2.16x
C O*S O ~
0 Fig. 2.
30 Mean width of ~
60 in canopy (m)
The relationship between the mean width of gaps in the tree canopy and the total numbers of butterflies seen per transect.
transects along paths with narrow or no gaps in their canopies. The width of the gaps explained 45% of the observed variation in butterfly numbers between transects (r = 0.67, df = 20, p < 0.001). DISCUSSION The results of this study suggest that woodland management intended to benefit the holding capacity and shooting of pheasants in the winter can also provide better habitats for many of the woodland butterflies during the summer months. The most simple method of improving an area of unmanaged woodland for pheasants is to remove some of the standards to increase the penetration of light to the woodland floor. The resultant increase in the ground flora provides a preferred habitat for pheasants (Robertson, 1985, 1986) while an open canopy has been shown in this study a n d by Pollard (1982) and Warren (1985) to be an important factor influencing butterfly abundance. Only 2% of the woodlands in Dorset still provide the sunny open conditions that are essential for most of the traditional species of woodland butterflies, the remainder being shadier than at any time 'in the last thousand years or more' (Thomas & Webb, 1984). Many species of butterfly associated with such open woodland have declined during the latter half of this century,
164
P. A. Robertson, M. L A. Woodburn, D. A. Hill
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166
P. A. Robertson, M. I. A. Woodburn, D. A. Hill
while those more tolerant of shade, such as the white admiral Lagoda camilla and speckled wood, have increased. Indeed, Heath et al. (1984) state that the recent spread of the few species that require more shady conditions reinforces the belief that it is alterations in woodland structure that have been of paramount importance in determining changes in the status of these butterflies. The large rides created as stands for shooting attracted large numbers of butterflies in this study, including many grassland species as well as those associated with woodlands. In fact these rides contained higher densities of grassland species than did those woodland/field edges sampled. This may be due to their sheltered position as well as the absence of pesticides, which may reduce butterfly abundance in many agricultural habitats (Rands & Sotherton, 1986). A survey conducted by Cobham Resource Consultants (1983) states that of over 400 small woodland owners questioned as to their reasons for retaining and planting small woods, 67% and 56% respectively specified that game was one of the motives, placing it second only to landscaping, and above commercial timber production, shelter, fuel wood, wildlife conservation, screening, recreation and fox hunting. Many species of woodland butterflies are suffering from the decline in the area of managed broadleaved woodland. The value of woodlands for game is greatly appreciated by landowners while management for pheasants is also beneficial for many of the declining species of butterflies. The encouragement and education of landowners to manage their woodlands for pheasants may benefit butterflies and other species of wildlife associated with more open woodland habitats.
ACKNOWLEDGEMENTS Thanks are due to Lord Shaftsbury for permission to work on his estate; to Dick Potts, Nick Sotherton and John Dover for commenting on earlier drafts and to Don Ford and Phillipa Bond for their help.
REFERENCES Cobham Resource Consultants (1983). Countryside sports, their economic significance. The Standing Conference on Countryside Sports, Reading. Gray, N. (1986). Woodland management for pheasants and wildlife. David and Charles, London, p. 176. Hall, M. (1981). The butterfly monitoring scheme. Institute of Terrestrial Ecology, Huntingdon.
Pheasant woodland management and butterflies
167
Heath, J., Pollard, E. & Thomas, J. A. (1984). Atlas of butterflies in Britain and Ireland. Viking, Harmondsworth, p. 158. Hill, D. A. & Edwards, J. (1986). The compatibility of pheasant management and woodland conservation with emphasis on Southern English coppice. Paper presented at the Recreation Ecology Research Group meeting, Wye College, Kent, April 1986. Pollard, E. (1977). A method for assessing changes in the abundance of butterflies. BioL Conserv., 12, 115-24. Pollard, E. (1982). Monitoring butterfly abundance in relation to the management of a nature reserve. Biol. Conserv., 24, 317-28. Rands, M. R. W. & Sotherton, N. W. (1986). Pesticide use on cereal crops and changes in the abundance of butterflies on arable farmland in England. Biol. Conserv., 36, 71-82. Robertson, P. A. (1985). Habitat selection and the relative distributions of wild and released pheasants (Phasianus colchicus) as determined by winter trapping. J. Worm Pheasant Assoc., 10, 87-99. Robertson, P. A. (1986). The ecology and management of hand-reared and wild pheasants (Phasianus colchicus) in Ireland. PhD thesis, National University of Ireland. Shoard, M. (1980). The theft of the countryside. Temple Smith, London, p. 260. Thomas, J. & Webb, N. (1984). Butterflies of Dorset. Dorset Natural History and Archaeological Society, Dorchester, p. 128. Warren, M. S. (1976). The Dorset woodlands--their history and conservation. M Sc thesis, University College, London. Warren, M. S. (1985). The influence of shade on butterfly numbers in woodland rides, with special reference to the wood white Leptidea sinapis. Biol. Conserv., 33, 147-64.