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Increased sheep numbers and the loss of heather moorland in the Peak District, England
BiologicalConservation20 ( 1981) 195 213
INCREASED SHEEP NUMBERS AND THE LOSS OF HEATHER MOORLAND IN THE PEAK DISTRICT, ENGLAND
P. ANDERSON
Gwynfa, Buxton Road, Chinley, StockportjSK12 6DR, Great Britain & D. W. YALDEN
Department of Zoology, Williamson Building, The University, Manchester MI3 9PL, Great Britain ABSTRACT
The maps of vegetation in the northern Peak District given by Moss (1913) suggest that there were then the equivalent of 154 km 2 of moorland dominated by heather and bilberry. A t present, the same area has the equivalent of only 99 km 2 of this moorland, a loss of 36 %. Sheep numbers in the hillparishes trebled between 1930 and 1976, and the changes in vegetation are consistent with those produced elsewhere, experimentally, by sheep grazing. It is considered thereJbre that these changes are cause and effect. The repercussions on wildlife of this loss of moorland are largely undocumented, but red grouse stocks seem to have declined to about a third of their 1930s level.
INTRODUCTION
Though there have been several brief allusions to the loss of heather moorland in the Peak District (e.g. Yalden, 1972; Orford, 1973), no attempt has previously been made to quantify this change. The early vegetation surveys by Moss (1913) included maps which cover much (though not all) of the moorland in the Peak District, and invite comparison with the present state of the moorland. Heather moorland, in the Peak District as elsewhere, is largely the result of management by shooting interests for red grouse Lagopus lagopus. The sharp decline in grouse bags on Peak District moors has been documented by Picozzi (1971), who also pointed out that heather management was, by Scottish standards, often poor. Yalden (1972) drew attention to the trebling of sheep numbers in the moorland parishes which had occurred between 1930 and 1970, and suggested that 195 Biol. Conserv. 0006-3207/81/0020-0195/$02"50 Printed in Great Britain
© Applied Science Publishers Ltd, England, 1981
196
P. A N D E R S O N , D. W . Y A L D E N
this might explain both the loss of heather moorland and the decline of red grouse stocks. This paper attempts to quantify the change in moorland vegetation, update the sheep statistics to 1977, and discuss the significance of the changes for red grouse and other wildlife.
METHODS AND SOURCES
The essential basis for this paper is the northern map provided by Moss (1913). This shows the major vegetation types at a scale of 1 : 63,360. Modern mapping of plant communities is usually much more detailed, and carried out at scales of I : 10,000 or 1: 25,000; these scales are, in practice, much easier to use since such details as field boundaries are shown. To facilitate the comparison, Moss's maps were redrawn at 1:25,000, and recent information synthesised to the same scale. The present-day maps amalgamate data from several sources. All the moorland has been surveyed by one or both of us in recent years, though not necessarily mapped. The Longdendale catchment has been mapped at 1 : 10,000 (P.A.) and the Kinder Bleaklow Site of Special Scientific Interest (SSSI) was mapped by Brunstrom (1976); both used ground survey and black-and-white air photographs while, for the SSSI, large-scale colour air photographs became available in 1977. Obscure boundaries, particularly on the black-and-white photographs where heather Calluna vulgarts merges into crowberry l~mpetrum nigrum or bilberry Vaccinium myrtillus, have been checked on the ground. Since the basic aim has been to provide a comparison with Moss (I 913), we have tried to match his plant communities. Five categories concern us particularly: (a) (b)
Calluna dominant ('heather moor' of Moss, 1913). Calluna and Eriophorum co-dominant ('mixed cotton-grass and heather moor').
(c) (d)
(e)
Calluna/grasses co-dominant ('siliceous grassland with much heather'). Vaccinium dominant ('bilberry moor'). Vaccinium and Calluna co-dominant ('mixed bilberry and heather moor').
We found it necessary to add a sixth category, (f)
Vaccinium--grassland co-dominant,
which Moss did not explicitly map. The areas covered by the major plant communities in each parish have been measured by overlaying the 1:25,000 maps with transparent graph paper and counting the millimetre squares. Sheep statistics have been obtained from the June census returns submitted to the Ministry of Agriculture, Fisheries and Food (MAFF). These returns are presented as parish statistics to preserve confidentiality. Data from 1930 to 1960 were obtained
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
197
from the Public Records Office, more recent data from local M A F F offices and the M A F F Statistical Division, Guildford. Seven categories of sheep are entered in the returns, but only the figure for total sheep, including lambs, is used here.
RESULTS
Vegetation mapping The 'moorland vegetation' (as considered in this paper) covers, on Moss's maps, a total of 176km 2. A simplified version of his map appears as Fig. 1. The current situation, shown (also simplified) in Fig. 2, is of 111 km 2. If areas where heather is codominant are scored as half, the figures are, respectively, 155 km z (1913) and 99 km 2 (1979). Using these weighted figures, this suggests a net loss of the equivalent of 56 km z, and that the present moorland has only 64 ~o of its former extent (Table 1). This is a net figure, covering both losses and gains; these are mapped separately in Fig. 3. It is also clear from Table 1 that the different communities have been affected to different degrees. Over 39 km z, 33 ~ of the former heather-dominated areas, have been lost, particularly on sloping, well-drained mineral soils as in Charlesworth and Outseats (Table 2). These have been replaced by grassland communities, mostly Deschampsia flexuosa with some Nardus stricta and bilberry Vaccinium myrtillus. Bracken Pteridium aquilinum has invaded many of the sheltered cloughs and valley sides. Over 77 ~o of the former 'siliceous grassland with much heather' has also been reduced to grassland, usually of Nardus stricta with Deschampsiaflexuosa. Stunted mats of Vaccinium myrtillus are frequent in these communities, which are most evident on the steeper valley sides. Moss also maps the summit of Bleaklow as 'grassland with much heather'. This area has been denuded of all its peat and much of its vegetation; there is now no heather, but a sparse community of crowberry Empetrum nigrum, with Vaccinium myrtillus, Nardus stricta, Deschampsia flexuosa and Juncus squarrosus. The mixed heather-bilberry community formerly fringing the whole Kinder Scout plateau has largely gone from the western side, but persists quite luxuriantly in Edale and parts of Hope Woodlands. The area formerly mapped along Derwent Edge is now dominated by heather, while that on Bamford Edge is a bracken bed. Moss described the bilberry moors as 'characteristic...on the rocky slopes surrounding the Peak' and 'on the high, bleak and windswept ridges and peaks of the sandstone hills' (1913, p. 182). Overall, 46 ~o of this vegetation type has been lost. On the ridges, Vaccinium myrtillus is still a significant component of the community but Empetrum nigrum is now dominant or at least co-dominant. On the slopes, the quantity of Vaccinium has declined to produce a mixed Deschampsia Vaccinium community, often including Nardus stricta. Table 1 includes 278 ha of this community which has been derived from what Moss (1913) mapped as Vaccinium moorland.
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TABLE l AREAS OF MOORLAND VEGETATION IN 1 9 1 3 AND 1 9 7 9 . MAPPED AT 1 : 2 5 , 0 0 0 , FIGURES R O U N D E D TO THE NEAREST HECTARE
Calluna dominant Calluna-Eriophorum co-dominant Calluna-grasses co-dominant Calluna-Vaccinium co-dominant Vaccinium dominant Vaccinium-grasses co-dominant Totals (unweighted) Totals (weighted. co-dominant
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8096 1530 459 325 393 278 11081 9949
32.6 34.7 77-3 40.3 46.0 -37.2 35.7
2
In compensation for some of these losses, there has been a considerable expansion of heather into areas formerly dominated by cotton grass Eriophorum vaginatum. This has either produced a mixed community, as in the higher parts of Charlesworth and Langsett parishes (Table 2), or proceeded to complete heather domination as in Dunford. In a very few cases (e.g. Win Hill, Hope parish) heather has increased at the expense of grassland. The most anomalous figures are those for Tintwistle (Table 2), which show only a slight decrease in moorland over the period. This results from a large forestry enclosure, the ground of which is, at present, mostly heather and bilberry. We have therefore mapped it as moorland, but it is likely to diminish as the trees attain full size. The data for Edale are also rather curious; overall loss of moorland has been modest, but the surviving moorland seems to have changed from including much mixed heather bilberry moor to communities of either heather or bilberry. These changes concern the overall extent of vegetation types, but there have probably also been changes in the quality of the vegetation. This is less apparent with heather, which either thrives, under light grazing, or is suppressed, by heavy grazing. Bilberry, however, can survive as a short, tightly grazed 'turf'. Photographs in Moss (1913) suggest that bilberry formerly existed as luxuriant tussocks, a growth-form nowadays most evident on ungrazed roadsides. There is no way of telling whether all of the former bilberry moor was of this type, though it seems most likely. One can, even now, find such bilberry in protected sites such as rocky ledges on steep clough sides. Similarly, heather persists in areas where it has otherwise disappeared, on railway embankments, rocky ledges, and protected roadsides (Brunstrom, 1976).
Sheep numbers The increase in sheep stocks for the main parishes which contribute to the KinderBleaklow moorlands (the Derbyshire parishes of Hayfield, Chinley Buxworth & Brownside, Edale, Derwent, Hope Woodlands and Charlesworth (Fig. 4)) is illustrated in graph form in Fig. 5; a comparison of the sheep stocks for the 1930s and
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Fig. 4. The principal moorland parishes of the Kinder-Bleaklow area. Land over 1500 foot, open stipple; reservoirs, dense stipple; broken line, boundary of the Peak District National Park. B = Bradfield. C = Charlesworth. CBB = Chinley Buxworth & Brownside. D = Derwent. E = Edale. H = Hayfield. HW = Hope Woodlands. L = Langsett. T = Tintwistle. The hatched area on the Derwent-Bradfield boundary is the Hey Clough basin studied by Evans (1977).
1970s, for these and some other parishes, is made in Table 3. For the KinderBleaklow area, the sheep population was fairly steady at around 17,000 animals during the 1930s, but then increased steadily to 25,000 in the mid-1950s and more steeply to 60,000 in 1976; only the severe winters of 1947 and 1969 caused major, but temporary, interruptions in this increase. However, the latest figures, for 1977, show a small drop compared with 1976, and it is possible that in the Peak District sheep stocks have reached a ceiling, at least under present economic and agricultural conditions. The individual parishes which contribute to this increase all show essentially the same pattern (Fig. 6). Some parishes, e.g. Charlesworth, had very low sheep stocks in the 1930s and show an increase throughout the 50-year period, rather than a plateau in the 1930s followed by an increase. All parishes show a sharp decline in 1947 as a result of the severe winter, but the 1969 winter seems at first glance to have had a more selective effect. While most parishes showed a sharp decrease then, that in Edale occurred the previous year; Edale is a small parish with a very high stocking rate (Table 2), and the 1968 winter was, in terms of frost and snow days, almost as severe as 1969 (Evans, 1977). Hayfield showed no decline in sheep numbers in 1969,
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Fig. 5. Changes in total sheep (including lambs), lambs, and the proportion of these two, for the Kinder Bleaklow area, 193(~ 1977 (parishes of Charlesworth, Hayfield, Chinley Buxworth & Brownside, Edale, Hope Woodlands and Derwent combined). Lambs now contribute about 41 °/o of the June flock.
but did so over the next two years; this parish appears to have been comparatively lightly stocked even in 1969, and we understand that the declines in 1970 and 1971 stem from changes of farm ownership and management rather than winter mortality. The rate of recovery from the 1969 low also varied between parishes; in Hope Woodlands, Edale and Charlesworth, sheep numbers were back to their 1968 levels by 1971, but in other parishes not until 1974 or 1975. The fact that sheep numbers have increased is not, of itself, sufficient to suggest that vegetation changes are a consequence. Much would depend on the area of grazing available, increases in improved pasture and possibly changes in management. In fact, the major changes seem to have been a loss of grazing over the 50 years, either to afforestation or, in the Derwent valley, to reservoirs. The mapping of the moorland edge by Parry (1977) does not suggest any increase in the amount of improved pasture between 1935 and 1970. Table 3 includes the map areas (ignoring slopes, that is) of the civil parishes, and the crude stocking densities calculated from them. It is recognised that these give only a rough estimate of the grazing pressures: some--perhaps many--sheep are enclosed on improved or semi-improved pasture at lower altitudes than the moorlands; sheep censused at a farm in one parish may actually graze in a neighbouring parish. However, since the moorland is not
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~o Fig. 6. Changesin total sheep for some of the Kinder-Bleaklow parishes (abbreviated as on Fig. 4), 1930-1977. The vertical axis on this figure has no absolute values, though it is calibrated in units of 1000 sheep; the graphs of each parish commence at a false origin, so that the rates, and periods, ~f increase can be compared. All these were affected by the 1947 winter, but note that Hayfield was apparently not affected in 1969.
subdivided by fences or walls, either between parishes or, in most cases, between estates, it is not possible to use parish sheep statistics in a n y more precise m a n n e r , a n d aggregating the figures for the whole of the K i n d e r - B l e a k l o w m o o r l a n d does provide a general s t a t e m e n t of stocking density. This says that from 0-7 sheep/ha in the 1930s, the stocking rate has increased to 2.07 sheep/ha. It must be added that the sheep in the Peak District are n o t removed from the m o o r l a n d in winter, a n d a l t h o u g h the grazing density will be lower overwinter after m u c h of the l a m b crop
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
207
has been sold, this density is not for 'summer only' grazing as it is in many other moorland sites which have been studied (e.g. Moor House National Nature Reserve, Rawes & Welch, 1969).
Possible correlation of the loss of moorland with the increase in sheep Superficially, there appears to be a good correlation between the loss of moorland and increase in sheep. For example, Charlesworth parish shows a six-fold increase in sheep and has lost 547 ha of moorland, while Outseats, with a slightly larger increase in sheep stocks, has lost over 1000ha, 88~. It ought therefore to be possible to strengthen our argument by demonstrating a statistical correlation between the two sets of figures. In practice such attempts founder because of other complications confounded with the crudity of parish sheep statistics. We have attempted to correlate absolute increases in sheep with absolute losses in moorland, proportionate increases with proportionate losses, and recent grazing densities of sheep with both absolute and proportionate losses of moorland. A closer examination of the figures in Tables 2 and 3 in fact make it obvious that this would be impossible. For example Bradfield has suffered the largest absolute loss of moorland, over 1700 ha, but this is a modest proportionate loss (35 ~o), correlated with a fairly modest increase in sheep and a low stocking density. Yet Bradfield is a very large parish, and still has a greater area of surviving moorland than any other. Conversely, Chinley Buxworth and Brownside has lost all of its moorland, but this is insignificant in absolute terms because it is a small parish and only had a small area of moorland to lose. Edale and Hope Woodlands show, in absolute terms, the greatest increases in sheep stocks but modest losses, both absolutely and proportionately, of moorland. In part, these difficulties result from management practices in different parishes or, more especially, on different estates within parishes. Some moors have deliberately limited or excluded sheep in order to further grouse stocks; the low sheep density in Langsett and increase in moorland there seem attributable to this, while the low sheep densities in Bradfield, Bamford and Hayfield are correlated with large areas of well-managed grouse moors in those parishes. The effect of management, i.e. forestry enclosures, in Tintwistle has already been indicated. A second major complication is the selective pattern of grazing which sheep in open-range conditions adopt. For example, Evans (1977) reported sheep densities on different vegetation regions in his study area, averaged over 2½years, of between 1-67 sheep/ha (on burnt heather moor) and 4.54 sheep/ha (on Agrostis-Festuca grassland with heather). At Moor House, Rawes & Welch (1969) recorded densities in summer-only grazings, between 0.04 sheep/ha (on blanket bog) and 8-7 sheep/ha (on Agrostis-Festuca grassland). Similar variations on Welsh hill grazings were reported by Jones (1967). Thus the range of grazing densities which the sheep themselves adopt, under free-range systems, far exceeds the range in densities between different parishes listed in Table 3.
208
P. ANDERSON, D. W. YALDEN DISCUSSION
Reality of the changes Initial reactions to the suggestion (Yalden, 1972) that sheep stocks in the moorland parishes of the Peak District had trebled between 1930 and 1970 were sceptical. It was argued that, pre-war, when grazing rents were paid by tenant farmers 'per head of sheep', there was a tendency for them to under-estimate the number of sheep present; since 1952, with the payment of hill sheep subsidies 'per ewe on the hill', there would be a tendency to submit a generous estimate. If this were true, it could of course produce the trend seen in Fig. 5. The argument seems, however, to be quite unrealistic. The statistics for each parish are compiled by M A F F from the census returns submitted by each farmer, individually and confidentially. There may be anything from 20 to (in Bradfield) 160 farms represented per parish, and there are at least 46 sheep farms in the Peak District (Peak District National Park 1974, map 4.1) as well as mixed farms. The pattern of increasing sheep stocks is seen in each of the six parishes contributing to Fig. 5, and in a further 21 moorland parishes documented by Yalden (1972). It seems quite unplausible that some 600 or so farmers, each acting independently, could produce such a consistent trend. It was also argued that sheep stocks in the 1930s were particularly low due to the depression. In fact, between 1920 and 1940, they were essentially stable, around a mean of 17903 (range 16214 to 20494), in the Kinder-Bleaklow parishes (R. Evans, pers. comm.). The acceptance of our figures for vegetation changes could also be questioned, perhaps with more justification. How accurate was Moss's (1913) map, how faithfully does our concept of vegetation communities match his, and have the changes which we suggest really occurred, or do they result from differences in method ? Moss must have carried out his survey on foot, and certainly did not have the benefit of aerial survey. However, given that sufficient time is available, field survey is by far the most reliable method of mapping; although aerial survey is very useful for mapping the edges of vegetation patches, the nature of those plant communities generally still needs to be checked on the ground. In places, the boundaries which Moss mapped, especially the lower edges of Calluna moorland, exactly match those which we find. The most likely source of error, as we have found, is in placing the upper edges of Calluna- and Vaccinium-dominated areas; frequently these grade into Empetrurn heath or mixtures of these three with Eriophorum. The featureless nature of many moorlands adds to the difficulty of mapping boundary lines. However, the major difference between Moss's survey and ours, in this respect, is that we found Calluna to have spread uphill into what he mapped as pure cottongrass areas. If this in any way results from a mapping error on his part (and we would stress that we have no direct evidence that he was anything other than accurate), then
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
209
its effect would be to minimise, rather than exaggerate, the overall loss of heather moorland which we report. Independent confirmation of the accuracy of his maps and of the reality of the change is provided by the Ordnance Survey maps, notably the 1912 edition which he used as a base map, and later editions. There are 25 shooting cabins labelled on the 1912 edition, and a further 13 shown on later editions (Fig. 1). These are all in areas which Moss ( 1913) mapped as moorland vegetation, and would hardly have been built unless they were near reasonable red grouse stocks. Most of them are now in ruins or have vanished entirely, and at least 17 of them are now in grassy areas where it would not be worth building a shooting cabin. (The presence now of only 7 or 8 functional cabins is not independent evidence of the reality of the change in vegetation, in the way that the siting of former cabins is, because the greater mobility conferred by vehicles makes it easier to retreat from the moorland and less essential to have a cabin nearby.)
Sheep and vegetation change The loss of heather from areas formerly of mixed grassland and heather, and the conversion of heather moors on mineral soil into grassland, are exactly the changes which various studies have shown to be likely to result from sheep grazing. Most notably, Jones (1967) documented the increase of heather and bilberry on hill land in Wales when sheep were excluded for 15 years, and their virtual disappearance when sheep grazing was resumed for a further 12 years. He did not give grazing densities for this latter period, but Hewson (1977) has shown that summer-only grazing by sheep at 3-28/ha will suppress heather growing on mineral soils, whereas at 2-18/ha heather increases. Evans (1977) observed sheep grazing on two heather communities at 1-67 and 2.17sheep/ha, on average, throughout the year; the highest density observed, in summer, was 3.23 sheep/ha. It seems, from the figures in Table l and from observations in the field, that bilberry withstands moderate sheep grazing better than heather; although grazing reduces it to a tight sward which is barely able to flower or fruit, its vegetative reproduction does allow it to spread. Indeed, one might extrapolate the same result from Jones' (1967) results; his Table 12 shows that, when lightly grazed or mown, the bilberry in moorland vegetation grows'as well as heather, whereas in ungrazed or unmown vegetation the heather does twice as well as bilberry. It is also possible that the spread of heather into pure cotton-grass areas is, indirectly, the result of sheep grazing, though this is more speculative. In some parts of the Peak District (e.g. Danebower Moss SK 0070), grouse management includes digging drainage ditches to foster the spread of heather into cotton-grass areas. Elsewhere in the moorlands, extensive gulley systems which cut back into cottongrass areas could have allowed heather to spread in the same way. The cause of this gulley development is controversial, but it is known to be a fairly recent phenomenon, of perhaps the last 300 vears [Tallis, 1973), and Shimwell (1974) has argued that it results from damage to the blanket-bog vegetation by sheep.
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P. ANDERSON, D. W. YALDEN
Timing of these changes There is, at present, little direct evidence on the period when these vegetation changes occurred. Two independent witnesses, one a naturalist, the other a gamekeeper, remember the heather-bilberry slopes of the western face of Kinder being burnt, for grouse management, in the late 1930s. This corresponds with the information, from another gamekeeper, that there were two keepers managing that area in the 1930s (Yalden, 1972); further, the presence of gamekeepers on various other moors at that time strongly suggests that the moorland mapped by Moss (1913) was still essentially present in the late 1930s. Since both the decrease in gamekeepers and the increase in sheep seem to be wartime and post-war changes, it seems very likely that most of the change in vegetation has also occurred in the last 40 years.
Effects on other wildlifi, The results of these vegetation changes for other species can, in most cases, only be guessed, and it is seldom clear whether vegetation change itself or more simply the change in management is the cause. The golden plover Pluvialis apricarius has disappeared from some, at least, of its former breeding sites; in particular Abney Moor, formerly a managed grouse moor, had 20 pairs which nested in the very short, recently burnt, patches of heather. The species ceased to breed there about 1952 (Yalden, 1974), and the moor has now only rank heather. The mountain hare Lepus timidus was introduced as an extra attraction for sportsmen around the 1870s. Heather forms an important part of its diet, and in particular it prefers to graze areas of very short, recently burnt, heather (Hewson, 1962). Game bags of hares have not been regularly recorded, but two neighbouring moors yielded bags of 119 and 131 in 1934, and one of them a further 104 hares in 1935. The hare population of that area is unlikely to exceed 70 now, and the species is surely less common (Yalden, 1971). The most direct evidence is that concerning the red grouse Lagopus lagopus scoticus. The game bags documented by Picozzi (1971) show a large decline between the pre-war and post-war levels. Using the figures for the seven moors with the most complete records, for the years 1935-1939, the average annual bag was 8390 birds. For the same seven moors in the years 1970-1974, the bag was 3462. Since average game bags do reflect the population size reasonably well (Picozzi, 1968), one may conclude that the grouse population was around 2-4 times higher in the 1930s than now. The recent August (post-breeding) population has been estimated at 60,500 (Yalden, 1979), implying a former August population of 145,200 grouse, and a loss since then of around 85,000. However, this is a minimal estimate, since it refers only to grouse lost from areas which were, and still are, grouse moors; areas no longer managed would perhaps have suffered a total loss of grouse. An estimate of this further loss might be made from our figure of 55 km 2 of'lost' moorland (though this loss refers to part, only, of the Peak Park moorland). If this formerly carried a density of 100 pairs/km 2, and these produced on average 2 young
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
211
per adult in August (Jenkins et al., 1967), the loss of grouse might be 33,000. The evidence of the same bags, above, suggests that the density of breeding grouse on well-managed moors in the 1930s was in fact much higher than 100 pairs/km z, though this would now be a very good density. Combining this figure with that above suggests a tentative estimate for the overall loss of around 118 thousand (August) grouse. An independent approach to this figure can be derived by making the, admittedly unlikely, assumption that sheep and grouse are in direct and absolute competition for food. Red grouse do indeed feed almost entirely on heather when it is available; observations of them feeding in the wild, throughout the year, suggest that a cock requires 60 g (dry matter) of heather daily (Savory, 1978). Similar observations on sheep on the moor have not been made, but under laboratory conditions, male sheep will eat 40(~500 g (dry matter) of heather daily, as well as 200 g of grass if it is available (Milne, 1974). This implies that a sheep could eat 6.5 to 8 times as much heather as a red grouse. In 1968, the moorland parishes of the Peak District held 75,07l more sheep than they had in 1936 (39,841 in 1936, 114,912 in 1968--see graphs in Yalden, 1972). On this basis, sheep could have displaced from 488-600 thousand red grouse. Clearly these are likely to be overestimates, since many of these extra sheep will be on improved grassland, and even on moorland they would eat much grass. On the other hand, food consumption of sheep in the wild, particularly in winter, should be much higher than in the laboratory; at Moor House, in summer, Rawes & Welch (1969) estimated, with grazing cages, that each sheep was removing between 600 and 1600 g (dry matter) of vegetation daily. Extrapolating from the results of Milne et al. (1979) suggests that free-living sheep might eat 1300g (dry matter) of heather daily in summer when run on heather moorland. Either way, the most notable point is that these estimates, though larger, are at least of the same order of magnitude as that reached earlier, and strengthen the supposition that, indeed, there may be around 120 thousand fewer grouse available for the shooting season now than in the 1930s. This discussion implies competition between sheep and grouse for heather, and blames the increased sheep stocks for the loss of heather moorland. In fact all three effects are the result of a change, indeed a decline, in moorland management. There are now only half the number of gamekeepers that there were in the 1930s (Yalden, 1972), and the level of shepherding seems low. Certainly many walls are derelict, so that sheep grazing is no longer properly regulated. It is not clear whether increasing sheep stocks, prompted perhaps by the payment of the hill sheep subsidy'per ewe on the hill', made it less and less worthwhile to employ gamekeepers, and manage moors for grouse, or whether a loss of interest in grouse shooting meant that there was no longer any resistance to increasing sheep stocks. There is, however, clear evidence that interest in grouse management is increasing, and grouse bags have certainly increased since the early 1960s. Since heather moorland is ecologically much more attractive than poor Nardus-dominated grassland or overgrazed and eroding
212
P. ANDERSON, D. W. YALDEN
Deschampsia grassland, it is hoped that this trend will continue. The only species which seems likely to have benefited from the change is the wheatear Oenanthe oenanlhe, which favours bare rocky ground and tightly grazed grassland. By contrast, such typical species of the area as twite Acanthisflavirostris, ring ouzel Turdus torquatus, emperor moth Salurnia pavonia and bumble-bee Bombus monticola (B. lapponicus), as well as those mentioned earlier, are associated with heather and bilberry moorland; all are likely to benefit, along with red grouse, from better control of sheep grazing.
ACKNOWLEDGEMENTS
Information on moorland vegetation has come from several sources. The surveys undertaken for the Nature Conservancy Council by P.A. were made available by Dr A. C. Warne, as was a copy of the MSc thesis by Brunstrom (1976)." Access to air survey photographs was given by Dr Warne and for the Peak Park Joint Planning Board by Miss D. Tranter. Access to sheep statistics was granted by the Librarian of the Public Records Office, the Statistical Division of MAFF, Guildford, and by Mr R. Walsh in the Divisional Office at Bakewell, while Dr R. Evans provided statistics for the period 1914-1930. Mr J. A. G. Lees, Secretary to the Moorland Owners and Tenants Association, compiled updated figures on grouse bags. To all of these we express our gratitude.
REFERENCES BRUNSTROM, R. (1976). Vegetation and sheep grazing in the Kinder-Bleaklow SSSI, Derbyshire and Yorkshire. MSc thesis, University of London. EVANS, R. (1977). Overgrazing and soil erosion on hill pastures with particular reference to the Peak District. J. Br. Grass. Soc., 32, 65-76. HEWSON, R. (1962). Food and feeding habits of the mountain hare Lepus timidus scoticus Hilzheimer. Proc. Zool. Soc. Lond., 139, 515-26. H EWSON,R. (1977). The effect on heather Calluna vulgar& of excluding sheep from moorland in northeast England. Naturalist, 102, 133q5. JENKINS,D., WATSON,A. & MILLER,G. R. (1967). Population fluctuation in the red grouse Lagopus lagopus scoticus. J. Anita. Ecol., 36, 97-122. JONES,LL. I. (1967). Studies on hill land in Wales. Tech. Bull. Welsh Plant Breeding Station, A berystwyth, 2. MILNE, J. A. (1974). The effects of season and age of the stand on the nutritive value of heather (Calluna vulgaris (L.) Hull) to sheep. J. agric. Sci., Camb., 83, 231-8. MILNE,J. A., BAGLEY,L. & GRANT,S. A. (1979). Effects of season and level of grazing on the utilisation of heather by sheep, 2. Diet selection and intake. Grass and Forage Sci., 34, 45-53. Moss, C. E. (1913). The vegetation of the Peak District. Cambridge, Cambridge University Press. OREORD, N. (1973). Breeding distribution of the twite in central Britain. Bird Study, 20, 51-2, 121-6. PARRY, M. L. (1977). Mapping moorland change: aframework for land-use decisions in the Peak District. Bakewell. Peak District National Park. PEAK DISTRICT NATIONAL PARK (1974). Structure plan. Report of survey. Bakewell, Peak District National Park.
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
213
PIcozzx, N. (1968). Grouse bags in relation to the management and geology of heather moors. J. appl. Ecol., 5. 483-8. PIcozzl, N. (1971). Breeding performance and shooting bags of red grouse in relation to public access in the Peak District National Park, England. Biol. Conserv., 3, 211-15. RAWES, M. & WELCH, D. (1969). Upland productivity of vegetation and sheep at Moor House National Nature Reserve, Westmoreland, England. Oikos, Suppl., 11, 7-72. SAvogv, C. J. (1978). Food consumption of red grouse in relation to the age and productivity of heather. J. Anirn. Ecol., 47, 269-82. SmMWELL, D. W. (1974). Sheep grazing intensity in Edale, 1692 1747, and its effect on blanket peat erosion. Derbyshire Archaeol. J., 94, 35-40. TALLtS, J. H. (1973). Studies on southern Pennine peats, V. Direct observations on peat erosion and peat hydrology at Featherbed Moss, Derbyshire. J. Ecol., 61, 1-22. YALDEN, D. W. (1971). The mountain hare (Lepus timidus) in the Peak District. Naturalist, 918, 81 92. YALDEN, D. W. (1972). The red grouse (Lagopus lagopus scoticus Lath.) in the Peak District. Naturalist. 922, 89-102. YALDEN, D. W. (1974). The status of golden plover (Pluvialis apricarius) and dunlin (Calidris alpina) in the Peak District. Naturalist, 930, 81-91. YALDEN, D. W. (1979). An estimate of the number of red grouse in the Peak District. Naturalist, 104, 5 8.
INCREASED SHEEP NUMBERS AND THE LOSS OF HEATHER MOORLAND IN THE PEAK DISTRICT, ENGLAND
P. ANDERSON
Gwynfa, Buxton Road, Chinley, StockportjSK12 6DR, Great Britain & D. W. YALDEN
Department of Zoology, Williamson Building, The University, Manchester MI3 9PL, Great Britain ABSTRACT
The maps of vegetation in the northern Peak District given by Moss (1913) suggest that there were then the equivalent of 154 km 2 of moorland dominated by heather and bilberry. A t present, the same area has the equivalent of only 99 km 2 of this moorland, a loss of 36 %. Sheep numbers in the hillparishes trebled between 1930 and 1976, and the changes in vegetation are consistent with those produced elsewhere, experimentally, by sheep grazing. It is considered thereJbre that these changes are cause and effect. The repercussions on wildlife of this loss of moorland are largely undocumented, but red grouse stocks seem to have declined to about a third of their 1930s level.
INTRODUCTION
Though there have been several brief allusions to the loss of heather moorland in the Peak District (e.g. Yalden, 1972; Orford, 1973), no attempt has previously been made to quantify this change. The early vegetation surveys by Moss (1913) included maps which cover much (though not all) of the moorland in the Peak District, and invite comparison with the present state of the moorland. Heather moorland, in the Peak District as elsewhere, is largely the result of management by shooting interests for red grouse Lagopus lagopus. The sharp decline in grouse bags on Peak District moors has been documented by Picozzi (1971), who also pointed out that heather management was, by Scottish standards, often poor. Yalden (1972) drew attention to the trebling of sheep numbers in the moorland parishes which had occurred between 1930 and 1970, and suggested that 195 Biol. Conserv. 0006-3207/81/0020-0195/$02"50 Printed in Great Britain
© Applied Science Publishers Ltd, England, 1981
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P. A N D E R S O N , D. W . Y A L D E N
this might explain both the loss of heather moorland and the decline of red grouse stocks. This paper attempts to quantify the change in moorland vegetation, update the sheep statistics to 1977, and discuss the significance of the changes for red grouse and other wildlife.
METHODS AND SOURCES
The essential basis for this paper is the northern map provided by Moss (1913). This shows the major vegetation types at a scale of 1 : 63,360. Modern mapping of plant communities is usually much more detailed, and carried out at scales of I : 10,000 or 1: 25,000; these scales are, in practice, much easier to use since such details as field boundaries are shown. To facilitate the comparison, Moss's maps were redrawn at 1:25,000, and recent information synthesised to the same scale. The present-day maps amalgamate data from several sources. All the moorland has been surveyed by one or both of us in recent years, though not necessarily mapped. The Longdendale catchment has been mapped at 1 : 10,000 (P.A.) and the Kinder Bleaklow Site of Special Scientific Interest (SSSI) was mapped by Brunstrom (1976); both used ground survey and black-and-white air photographs while, for the SSSI, large-scale colour air photographs became available in 1977. Obscure boundaries, particularly on the black-and-white photographs where heather Calluna vulgarts merges into crowberry l~mpetrum nigrum or bilberry Vaccinium myrtillus, have been checked on the ground. Since the basic aim has been to provide a comparison with Moss (I 913), we have tried to match his plant communities. Five categories concern us particularly: (a) (b)
Calluna dominant ('heather moor' of Moss, 1913). Calluna and Eriophorum co-dominant ('mixed cotton-grass and heather moor').
(c) (d)
(e)
Calluna/grasses co-dominant ('siliceous grassland with much heather'). Vaccinium dominant ('bilberry moor'). Vaccinium and Calluna co-dominant ('mixed bilberry and heather moor').
We found it necessary to add a sixth category, (f)
Vaccinium--grassland co-dominant,
which Moss did not explicitly map. The areas covered by the major plant communities in each parish have been measured by overlaying the 1:25,000 maps with transparent graph paper and counting the millimetre squares. Sheep statistics have been obtained from the June census returns submitted to the Ministry of Agriculture, Fisheries and Food (MAFF). These returns are presented as parish statistics to preserve confidentiality. Data from 1930 to 1960 were obtained
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
197
from the Public Records Office, more recent data from local M A F F offices and the M A F F Statistical Division, Guildford. Seven categories of sheep are entered in the returns, but only the figure for total sheep, including lambs, is used here.
RESULTS
Vegetation mapping The 'moorland vegetation' (as considered in this paper) covers, on Moss's maps, a total of 176km 2. A simplified version of his map appears as Fig. 1. The current situation, shown (also simplified) in Fig. 2, is of 111 km 2. If areas where heather is codominant are scored as half, the figures are, respectively, 155 km z (1913) and 99 km 2 (1979). Using these weighted figures, this suggests a net loss of the equivalent of 56 km z, and that the present moorland has only 64 ~o of its former extent (Table 1). This is a net figure, covering both losses and gains; these are mapped separately in Fig. 3. It is also clear from Table 1 that the different communities have been affected to different degrees. Over 39 km z, 33 ~ of the former heather-dominated areas, have been lost, particularly on sloping, well-drained mineral soils as in Charlesworth and Outseats (Table 2). These have been replaced by grassland communities, mostly Deschampsia flexuosa with some Nardus stricta and bilberry Vaccinium myrtillus. Bracken Pteridium aquilinum has invaded many of the sheltered cloughs and valley sides. Over 77 ~o of the former 'siliceous grassland with much heather' has also been reduced to grassland, usually of Nardus stricta with Deschampsiaflexuosa. Stunted mats of Vaccinium myrtillus are frequent in these communities, which are most evident on the steeper valley sides. Moss also maps the summit of Bleaklow as 'grassland with much heather'. This area has been denuded of all its peat and much of its vegetation; there is now no heather, but a sparse community of crowberry Empetrum nigrum, with Vaccinium myrtillus, Nardus stricta, Deschampsia flexuosa and Juncus squarrosus. The mixed heather-bilberry community formerly fringing the whole Kinder Scout plateau has largely gone from the western side, but persists quite luxuriantly in Edale and parts of Hope Woodlands. The area formerly mapped along Derwent Edge is now dominated by heather, while that on Bamford Edge is a bracken bed. Moss described the bilberry moors as 'characteristic...on the rocky slopes surrounding the Peak' and 'on the high, bleak and windswept ridges and peaks of the sandstone hills' (1913, p. 182). Overall, 46 ~o of this vegetation type has been lost. On the ridges, Vaccinium myrtillus is still a significant component of the community but Empetrum nigrum is now dominant or at least co-dominant. On the slopes, the quantity of Vaccinium has declined to produce a mixed Deschampsia Vaccinium community, often including Nardus stricta. Table 1 includes 278 ha of this community which has been derived from what Moss (1913) mapped as Vaccinium moorland.
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Calluna dominant Calluna-Eriophorum co-dominant Calluna-grasses co-dominant Calluna-Vaccinium co-dominant Vaccinium dominant Vaccinium-grasses co-dominant Totals (unweighted) Totals (weighted. co-dominant
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In compensation for some of these losses, there has been a considerable expansion of heather into areas formerly dominated by cotton grass Eriophorum vaginatum. This has either produced a mixed community, as in the higher parts of Charlesworth and Langsett parishes (Table 2), or proceeded to complete heather domination as in Dunford. In a very few cases (e.g. Win Hill, Hope parish) heather has increased at the expense of grassland. The most anomalous figures are those for Tintwistle (Table 2), which show only a slight decrease in moorland over the period. This results from a large forestry enclosure, the ground of which is, at present, mostly heather and bilberry. We have therefore mapped it as moorland, but it is likely to diminish as the trees attain full size. The data for Edale are also rather curious; overall loss of moorland has been modest, but the surviving moorland seems to have changed from including much mixed heather bilberry moor to communities of either heather or bilberry. These changes concern the overall extent of vegetation types, but there have probably also been changes in the quality of the vegetation. This is less apparent with heather, which either thrives, under light grazing, or is suppressed, by heavy grazing. Bilberry, however, can survive as a short, tightly grazed 'turf'. Photographs in Moss (1913) suggest that bilberry formerly existed as luxuriant tussocks, a growth-form nowadays most evident on ungrazed roadsides. There is no way of telling whether all of the former bilberry moor was of this type, though it seems most likely. One can, even now, find such bilberry in protected sites such as rocky ledges on steep clough sides. Similarly, heather persists in areas where it has otherwise disappeared, on railway embankments, rocky ledges, and protected roadsides (Brunstrom, 1976).
Sheep numbers The increase in sheep stocks for the main parishes which contribute to the KinderBleaklow moorlands (the Derbyshire parishes of Hayfield, Chinley Buxworth & Brownside, Edale, Derwent, Hope Woodlands and Charlesworth (Fig. 4)) is illustrated in graph form in Fig. 5; a comparison of the sheep stocks for the 1930s and
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Fig. 4. The principal moorland parishes of the Kinder-Bleaklow area. Land over 1500 foot, open stipple; reservoirs, dense stipple; broken line, boundary of the Peak District National Park. B = Bradfield. C = Charlesworth. CBB = Chinley Buxworth & Brownside. D = Derwent. E = Edale. H = Hayfield. HW = Hope Woodlands. L = Langsett. T = Tintwistle. The hatched area on the Derwent-Bradfield boundary is the Hey Clough basin studied by Evans (1977).
1970s, for these and some other parishes, is made in Table 3. For the KinderBleaklow area, the sheep population was fairly steady at around 17,000 animals during the 1930s, but then increased steadily to 25,000 in the mid-1950s and more steeply to 60,000 in 1976; only the severe winters of 1947 and 1969 caused major, but temporary, interruptions in this increase. However, the latest figures, for 1977, show a small drop compared with 1976, and it is possible that in the Peak District sheep stocks have reached a ceiling, at least under present economic and agricultural conditions. The individual parishes which contribute to this increase all show essentially the same pattern (Fig. 6). Some parishes, e.g. Charlesworth, had very low sheep stocks in the 1930s and show an increase throughout the 50-year period, rather than a plateau in the 1930s followed by an increase. All parishes show a sharp decline in 1947 as a result of the severe winter, but the 1969 winter seems at first glance to have had a more selective effect. While most parishes showed a sharp decrease then, that in Edale occurred the previous year; Edale is a small parish with a very high stocking rate (Table 2), and the 1968 winter was, in terms of frost and snow days, almost as severe as 1969 (Evans, 1977). Hayfield showed no decline in sheep numbers in 1969,
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but did so over the next two years; this parish appears to have been comparatively lightly stocked even in 1969, and we understand that the declines in 1970 and 1971 stem from changes of farm ownership and management rather than winter mortality. The rate of recovery from the 1969 low also varied between parishes; in Hope Woodlands, Edale and Charlesworth, sheep numbers were back to their 1968 levels by 1971, but in other parishes not until 1974 or 1975. The fact that sheep numbers have increased is not, of itself, sufficient to suggest that vegetation changes are a consequence. Much would depend on the area of grazing available, increases in improved pasture and possibly changes in management. In fact, the major changes seem to have been a loss of grazing over the 50 years, either to afforestation or, in the Derwent valley, to reservoirs. The mapping of the moorland edge by Parry (1977) does not suggest any increase in the amount of improved pasture between 1935 and 1970. Table 3 includes the map areas (ignoring slopes, that is) of the civil parishes, and the crude stocking densities calculated from them. It is recognised that these give only a rough estimate of the grazing pressures: some--perhaps many--sheep are enclosed on improved or semi-improved pasture at lower altitudes than the moorlands; sheep censused at a farm in one parish may actually graze in a neighbouring parish. However, since the moorland is not
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~o Fig. 6. Changesin total sheep for some of the Kinder-Bleaklow parishes (abbreviated as on Fig. 4), 1930-1977. The vertical axis on this figure has no absolute values, though it is calibrated in units of 1000 sheep; the graphs of each parish commence at a false origin, so that the rates, and periods, ~f increase can be compared. All these were affected by the 1947 winter, but note that Hayfield was apparently not affected in 1969.
subdivided by fences or walls, either between parishes or, in most cases, between estates, it is not possible to use parish sheep statistics in a n y more precise m a n n e r , a n d aggregating the figures for the whole of the K i n d e r - B l e a k l o w m o o r l a n d does provide a general s t a t e m e n t of stocking density. This says that from 0-7 sheep/ha in the 1930s, the stocking rate has increased to 2.07 sheep/ha. It must be added that the sheep in the Peak District are n o t removed from the m o o r l a n d in winter, a n d a l t h o u g h the grazing density will be lower overwinter after m u c h of the l a m b crop
SHEEP NUMBERS AND LOSS OF HEATHER MOORLAND
207
has been sold, this density is not for 'summer only' grazing as it is in many other moorland sites which have been studied (e.g. Moor House National Nature Reserve, Rawes & Welch, 1969).
Possible correlation of the loss of moorland with the increase in sheep Superficially, there appears to be a good correlation between the loss of moorland and increase in sheep. For example, Charlesworth parish shows a six-fold increase in sheep and has lost 547 ha of moorland, while Outseats, with a slightly larger increase in sheep stocks, has lost over 1000ha, 88~. It ought therefore to be possible to strengthen our argument by demonstrating a statistical correlation between the two sets of figures. In practice such attempts founder because of other complications confounded with the crudity of parish sheep statistics. We have attempted to correlate absolute increases in sheep with absolute losses in moorland, proportionate increases with proportionate losses, and recent grazing densities of sheep with both absolute and proportionate losses of moorland. A closer examination of the figures in Tables 2 and 3 in fact make it obvious that this would be impossible. For example Bradfield has suffered the largest absolute loss of moorland, over 1700 ha, but this is a modest proportionate loss (35 ~o), correlated with a fairly modest increase in sheep and a low stocking density. Yet Bradfield is a very large parish, and still has a greater area of surviving moorland than any other. Conversely, Chinley Buxworth and Brownside has lost all of its moorland, but this is insignificant in absolute terms because it is a small parish and only had a small area of moorland to lose. Edale and Hope Woodlands show, in absolute terms, the greatest increases in sheep stocks but modest losses, both absolutely and proportionately, of moorland. In part, these difficulties result from management practices in different parishes or, more especially, on different estates within parishes. Some moors have deliberately limited or excluded sheep in order to further grouse stocks; the low sheep density in Langsett and increase in moorland there seem attributable to this, while the low sheep densities in Bradfield, Bamford and Hayfield are correlated with large areas of well-managed grouse moors in those parishes. The effect of management, i.e. forestry enclosures, in Tintwistle has already been indicated. A second major complication is the selective pattern of grazing which sheep in open-range conditions adopt. For example, Evans (1977) reported sheep densities on different vegetation regions in his study area, averaged over 2½years, of between 1-67 sheep/ha (on burnt heather moor) and 4.54 sheep/ha (on Agrostis-Festuca grassland with heather). At Moor House, Rawes & Welch (1969) recorded densities in summer-only grazings, between 0.04 sheep/ha (on blanket bog) and 8-7 sheep/ha (on Agrostis-Festuca grassland). Similar variations on Welsh hill grazings were reported by Jones (1967). Thus the range of grazing densities which the sheep themselves adopt, under free-range systems, far exceeds the range in densities between different parishes listed in Table 3.
208
P. ANDERSON, D. W. YALDEN DISCUSSION
Reality of the changes Initial reactions to the suggestion (Yalden, 1972) that sheep stocks in the moorland parishes of the Peak District had trebled between 1930 and 1970 were sceptical. It was argued that, pre-war, when grazing rents were paid by tenant farmers 'per head of sheep', there was a tendency for them to under-estimate the number of sheep present; since 1952, with the payment of hill sheep subsidies 'per ewe on the hill', there would be a tendency to submit a generous estimate. If this were true, it could of course produce the trend seen in Fig. 5. The argument seems, however, to be quite unrealistic. The statistics for each parish are compiled by M A F F from the census returns submitted by each farmer, individually and confidentially. There may be anything from 20 to (in Bradfield) 160 farms represented per parish, and there are at least 46 sheep farms in the Peak District (Peak District National Park 1974, map 4.1) as well as mixed farms. The pattern of increasing sheep stocks is seen in each of the six parishes contributing to Fig. 5, and in a further 21 moorland parishes documented by Yalden (1972). It seems quite unplausible that some 600 or so farmers, each acting independently, could produce such a consistent trend. It was also argued that sheep stocks in the 1930s were particularly low due to the depression. In fact, between 1920 and 1940, they were essentially stable, around a mean of 17903 (range 16214 to 20494), in the Kinder-Bleaklow parishes (R. Evans, pers. comm.). The acceptance of our figures for vegetation changes could also be questioned, perhaps with more justification. How accurate was Moss's (1913) map, how faithfully does our concept of vegetation communities match his, and have the changes which we suggest really occurred, or do they result from differences in method ? Moss must have carried out his survey on foot, and certainly did not have the benefit of aerial survey. However, given that sufficient time is available, field survey is by far the most reliable method of mapping; although aerial survey is very useful for mapping the edges of vegetation patches, the nature of those plant communities generally still needs to be checked on the ground. In places, the boundaries which Moss mapped, especially the lower edges of Calluna moorland, exactly match those which we find. The most likely source of error, as we have found, is in placing the upper edges of Calluna- and Vaccinium-dominated areas; frequently these grade into Empetrurn heath or mixtures of these three with Eriophorum. The featureless nature of many moorlands adds to the difficulty of mapping boundary lines. However, the major difference between Moss's survey and ours, in this respect, is that we found Calluna to have spread uphill into what he mapped as pure cottongrass areas. If this in any way results from a mapping error on his part (and we would stress that we have no direct evidence that he was anything other than accurate), then
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its effect would be to minimise, rather than exaggerate, the overall loss of heather moorland which we report. Independent confirmation of the accuracy of his maps and of the reality of the change is provided by the Ordnance Survey maps, notably the 1912 edition which he used as a base map, and later editions. There are 25 shooting cabins labelled on the 1912 edition, and a further 13 shown on later editions (Fig. 1). These are all in areas which Moss ( 1913) mapped as moorland vegetation, and would hardly have been built unless they were near reasonable red grouse stocks. Most of them are now in ruins or have vanished entirely, and at least 17 of them are now in grassy areas where it would not be worth building a shooting cabin. (The presence now of only 7 or 8 functional cabins is not independent evidence of the reality of the change in vegetation, in the way that the siting of former cabins is, because the greater mobility conferred by vehicles makes it easier to retreat from the moorland and less essential to have a cabin nearby.)
Sheep and vegetation change The loss of heather from areas formerly of mixed grassland and heather, and the conversion of heather moors on mineral soil into grassland, are exactly the changes which various studies have shown to be likely to result from sheep grazing. Most notably, Jones (1967) documented the increase of heather and bilberry on hill land in Wales when sheep were excluded for 15 years, and their virtual disappearance when sheep grazing was resumed for a further 12 years. He did not give grazing densities for this latter period, but Hewson (1977) has shown that summer-only grazing by sheep at 3-28/ha will suppress heather growing on mineral soils, whereas at 2-18/ha heather increases. Evans (1977) observed sheep grazing on two heather communities at 1-67 and 2.17sheep/ha, on average, throughout the year; the highest density observed, in summer, was 3.23 sheep/ha. It seems, from the figures in Table l and from observations in the field, that bilberry withstands moderate sheep grazing better than heather; although grazing reduces it to a tight sward which is barely able to flower or fruit, its vegetative reproduction does allow it to spread. Indeed, one might extrapolate the same result from Jones' (1967) results; his Table 12 shows that, when lightly grazed or mown, the bilberry in moorland vegetation grows'as well as heather, whereas in ungrazed or unmown vegetation the heather does twice as well as bilberry. It is also possible that the spread of heather into pure cotton-grass areas is, indirectly, the result of sheep grazing, though this is more speculative. In some parts of the Peak District (e.g. Danebower Moss SK 0070), grouse management includes digging drainage ditches to foster the spread of heather into cotton-grass areas. Elsewhere in the moorlands, extensive gulley systems which cut back into cottongrass areas could have allowed heather to spread in the same way. The cause of this gulley development is controversial, but it is known to be a fairly recent phenomenon, of perhaps the last 300 vears [Tallis, 1973), and Shimwell (1974) has argued that it results from damage to the blanket-bog vegetation by sheep.
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Timing of these changes There is, at present, little direct evidence on the period when these vegetation changes occurred. Two independent witnesses, one a naturalist, the other a gamekeeper, remember the heather-bilberry slopes of the western face of Kinder being burnt, for grouse management, in the late 1930s. This corresponds with the information, from another gamekeeper, that there were two keepers managing that area in the 1930s (Yalden, 1972); further, the presence of gamekeepers on various other moors at that time strongly suggests that the moorland mapped by Moss (1913) was still essentially present in the late 1930s. Since both the decrease in gamekeepers and the increase in sheep seem to be wartime and post-war changes, it seems very likely that most of the change in vegetation has also occurred in the last 40 years.
Effects on other wildlifi, The results of these vegetation changes for other species can, in most cases, only be guessed, and it is seldom clear whether vegetation change itself or more simply the change in management is the cause. The golden plover Pluvialis apricarius has disappeared from some, at least, of its former breeding sites; in particular Abney Moor, formerly a managed grouse moor, had 20 pairs which nested in the very short, recently burnt, patches of heather. The species ceased to breed there about 1952 (Yalden, 1974), and the moor has now only rank heather. The mountain hare Lepus timidus was introduced as an extra attraction for sportsmen around the 1870s. Heather forms an important part of its diet, and in particular it prefers to graze areas of very short, recently burnt, heather (Hewson, 1962). Game bags of hares have not been regularly recorded, but two neighbouring moors yielded bags of 119 and 131 in 1934, and one of them a further 104 hares in 1935. The hare population of that area is unlikely to exceed 70 now, and the species is surely less common (Yalden, 1971). The most direct evidence is that concerning the red grouse Lagopus lagopus scoticus. The game bags documented by Picozzi (1971) show a large decline between the pre-war and post-war levels. Using the figures for the seven moors with the most complete records, for the years 1935-1939, the average annual bag was 8390 birds. For the same seven moors in the years 1970-1974, the bag was 3462. Since average game bags do reflect the population size reasonably well (Picozzi, 1968), one may conclude that the grouse population was around 2-4 times higher in the 1930s than now. The recent August (post-breeding) population has been estimated at 60,500 (Yalden, 1979), implying a former August population of 145,200 grouse, and a loss since then of around 85,000. However, this is a minimal estimate, since it refers only to grouse lost from areas which were, and still are, grouse moors; areas no longer managed would perhaps have suffered a total loss of grouse. An estimate of this further loss might be made from our figure of 55 km 2 of'lost' moorland (though this loss refers to part, only, of the Peak Park moorland). If this formerly carried a density of 100 pairs/km 2, and these produced on average 2 young
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per adult in August (Jenkins et al., 1967), the loss of grouse might be 33,000. The evidence of the same bags, above, suggests that the density of breeding grouse on well-managed moors in the 1930s was in fact much higher than 100 pairs/km z, though this would now be a very good density. Combining this figure with that above suggests a tentative estimate for the overall loss of around 118 thousand (August) grouse. An independent approach to this figure can be derived by making the, admittedly unlikely, assumption that sheep and grouse are in direct and absolute competition for food. Red grouse do indeed feed almost entirely on heather when it is available; observations of them feeding in the wild, throughout the year, suggest that a cock requires 60 g (dry matter) of heather daily (Savory, 1978). Similar observations on sheep on the moor have not been made, but under laboratory conditions, male sheep will eat 40(~500 g (dry matter) of heather daily, as well as 200 g of grass if it is available (Milne, 1974). This implies that a sheep could eat 6.5 to 8 times as much heather as a red grouse. In 1968, the moorland parishes of the Peak District held 75,07l more sheep than they had in 1936 (39,841 in 1936, 114,912 in 1968--see graphs in Yalden, 1972). On this basis, sheep could have displaced from 488-600 thousand red grouse. Clearly these are likely to be overestimates, since many of these extra sheep will be on improved grassland, and even on moorland they would eat much grass. On the other hand, food consumption of sheep in the wild, particularly in winter, should be much higher than in the laboratory; at Moor House, in summer, Rawes & Welch (1969) estimated, with grazing cages, that each sheep was removing between 600 and 1600 g (dry matter) of vegetation daily. Extrapolating from the results of Milne et al. (1979) suggests that free-living sheep might eat 1300g (dry matter) of heather daily in summer when run on heather moorland. Either way, the most notable point is that these estimates, though larger, are at least of the same order of magnitude as that reached earlier, and strengthen the supposition that, indeed, there may be around 120 thousand fewer grouse available for the shooting season now than in the 1930s. This discussion implies competition between sheep and grouse for heather, and blames the increased sheep stocks for the loss of heather moorland. In fact all three effects are the result of a change, indeed a decline, in moorland management. There are now only half the number of gamekeepers that there were in the 1930s (Yalden, 1972), and the level of shepherding seems low. Certainly many walls are derelict, so that sheep grazing is no longer properly regulated. It is not clear whether increasing sheep stocks, prompted perhaps by the payment of the hill sheep subsidy'per ewe on the hill', made it less and less worthwhile to employ gamekeepers, and manage moors for grouse, or whether a loss of interest in grouse shooting meant that there was no longer any resistance to increasing sheep stocks. There is, however, clear evidence that interest in grouse management is increasing, and grouse bags have certainly increased since the early 1960s. Since heather moorland is ecologically much more attractive than poor Nardus-dominated grassland or overgrazed and eroding
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Deschampsia grassland, it is hoped that this trend will continue. The only species which seems likely to have benefited from the change is the wheatear Oenanthe oenanlhe, which favours bare rocky ground and tightly grazed grassland. By contrast, such typical species of the area as twite Acanthisflavirostris, ring ouzel Turdus torquatus, emperor moth Salurnia pavonia and bumble-bee Bombus monticola (B. lapponicus), as well as those mentioned earlier, are associated with heather and bilberry moorland; all are likely to benefit, along with red grouse, from better control of sheep grazing.
ACKNOWLEDGEMENTS
Information on moorland vegetation has come from several sources. The surveys undertaken for the Nature Conservancy Council by P.A. were made available by Dr A. C. Warne, as was a copy of the MSc thesis by Brunstrom (1976)." Access to air survey photographs was given by Dr Warne and for the Peak Park Joint Planning Board by Miss D. Tranter. Access to sheep statistics was granted by the Librarian of the Public Records Office, the Statistical Division of MAFF, Guildford, and by Mr R. Walsh in the Divisional Office at Bakewell, while Dr R. Evans provided statistics for the period 1914-1930. Mr J. A. G. Lees, Secretary to the Moorland Owners and Tenants Association, compiled updated figures on grouse bags. To all of these we express our gratitude.
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PIcozzx, N. (1968). Grouse bags in relation to the management and geology of heather moors. J. appl. Ecol., 5. 483-8. PIcozzl, N. (1971). Breeding performance and shooting bags of red grouse in relation to public access in the Peak District National Park, England. Biol. Conserv., 3, 211-15. RAWES, M. & WELCH, D. (1969). Upland productivity of vegetation and sheep at Moor House National Nature Reserve, Westmoreland, England. Oikos, Suppl., 11, 7-72. SAvogv, C. J. (1978). Food consumption of red grouse in relation to the age and productivity of heather. J. Anirn. Ecol., 47, 269-82. SmMWELL, D. W. (1974). Sheep grazing intensity in Edale, 1692 1747, and its effect on blanket peat erosion. Derbyshire Archaeol. J., 94, 35-40. TALLtS, J. H. (1973). Studies on southern Pennine peats, V. Direct observations on peat erosion and peat hydrology at Featherbed Moss, Derbyshire. J. Ecol., 61, 1-22. YALDEN, D. W. (1971). The mountain hare (Lepus timidus) in the Peak District. Naturalist, 918, 81 92. YALDEN, D. W. (1972). The red grouse (Lagopus lagopus scoticus Lath.) in the Peak District. Naturalist. 922, 89-102. YALDEN, D. W. (1974). The status of golden plover (Pluvialis apricarius) and dunlin (Calidris alpina) in the Peak District. Naturalist, 930, 81-91. YALDEN, D. W. (1979). An estimate of the number of red grouse in the Peak District. Naturalist, 104, 5 8.