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Changes in vegetation following reduction in grazing pressure on the National Trust's Kinder Estate, Peak District, Derbyshire, England
Biological Conservation 69 (1994) 55~3 © 1994 Elsevier Science Limited Printed in Great Britain. All rights reserved 0006-3207/94/$07.00 ELSEVIER
CHANGES IN VEGETATION FOLLOWING REDUCTION IN GRAZING PRESSURE ON THE NATIONAL TRUST'S KINDER ESTATE, PEAK DISTRICT, DERBYSHIRE, ENGLAND Penny Anderson & Elaine Radford Penny Anderson Associates, 52 Lower Lane, Chinley, Stockport, UK, SK12 6BD (Received 26 October 1992; revised version received 25 August 1993; accepted 1 September 1993)
plateau had been mapped by the Peak District's Moorland Erosion Project as fragile and eroding (Phillips et al., 1981). The 10-km grid square (SK08) in which the majority of Kinder lies contributed 1.78 km 2 to the 33.25 km 2 of eroded or partially eroded ground estimated by the study in the Peak District National Park. Most of the erosion in the moorlands as a whole was attributed to fire damage, but on the slopes west of Kinder both the vegetation change and the soil erosion resulted mostly from poorly controlled sheep grazing (Phillips et al., 1981).
Abstract A monitoring programme is described which charts the recolonisation of moorland vegetation on the slopes of the Kinder plateau (Peak District, Derbyshire, UK) after reduction of sheep grazing. Deschampsia flexuosa has spread substantially, and there have been parallel increases in biomass and numbers of flowering culms. Calluna vulgaris and Vaccinium myrtillus have also increased significantly, but changes in other moorland species were limited. The previously bare and eroding ground has largely been revegetated except on the steepest slope, and the community is reverting to that described for the area in 1913.
Sheep grazing pressure The Kinder Estate was purchased by the National Trust in 1982, and part of the Trust's management plan was to reduce sheep numbers on the moorland with the objective of encouraging recovery of the vegetation in areas that were fragile or eroding. More than 1500 sheep regularly grazed the 607 ha of these moors at this time (an average of 2.5 ewes ha-l). Given the recommended moorland grazing level of 1 ewe ha ~ (Phillips et al., 1981), this represents a high concentration of animals, bearing in mind the small proportion of more palatable and nutritious vegetation and the extent of bare ground. It was clear that the grazing pressure was concentrated for much of the year on the slopes below the plateau where some shelter was afforded from strong winds and rain, and where preferred species were concentrated. As a result, the vegetation cover was fragmenting and soils beginning to erode. The previous owners had attempted to reduce the grazing pressure by removing most of their sheep, and the majority still on the moor were trespassers from adjoining areas. This ingress was effectively reduced by the National Trust after 1982 by regularly gathering sheep and penning them to await collection by their owners. At the time, this was seen as a radical and controversial change in management, although revegetation trials had indicated the value of excluding grazing, amongst other treatments (Tallis & Yalden, 1983). Since there were few examples of long-term monitoring of the effects on vegetation of such a reduction in grazing, the Peak District Moorland Management Project
Keywords: Peak District, moorland, heather, grazing, restoration.
INTRODUCTION The nature of the site The Kinder Estate (1267 ha) lies within the moorland zone of the Peak District National Park (Fig. 1) and comprises part of the high plateau of Kinder Scout (at c. 635 m altitude) which is covered in blanket peat, flanked by steeper slopes bearing mineral soils and peaty podzols. The extensively eroded peat haggs and groughs (the dissected peat mounds and channels) of the plateau support fragmented communities of the cotton-grasses Eriophorum vaginatum and E. angustifolium, bilberry Vaccinium myrtillus and crowberry Empetrum nigrum. There is much bare peat and, in places, the underlying regolith is now exposed, and has been only superficially colonised by scattered moorland plants including wavy hair-grass Deschampsia flexuosa and mat-grass Nardus stricta. In 1982, the western slopes below the plateau were mostly covered by a discontinuous D. flexuosa turf intermingled with patches of N. stricta, V. myrtillus and bare ground. The state of the slopes at this time contrasted markedly with the situation in 1913 when they were mapped by Moss (1913) as a Vaccinium myrtillus/ Calluna vulgaris community. In 1979, the whole of the west side of the Kinder 55
P. Anderson, E. Radford
56
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Fig. 1, The location of the groups of transects (O A, B and C) within the National Trust's Kinder Estate ( - - Estate boundary) and Edale Road bank (&) on which Vaccinium myrtillus flowers were counted. Contours shown - - 550 and 600 m. Inset shows the general location of Kinder. (which had evolved from the Moorland Erosion Study) commissioned the present study. Its principal objective was to monitor the effectiveness of shepherding as a means of securing revegetation of eroding ground without the expense of fencing, or supplementary treatment with seed or fertilizers. This would enable the Moorland Management Project to demonstrate the effects and value of such a change in management tO other land managers. Plant names follow those used in Clapham et al. (1987). METHODS Sheep control programme
Between 1983 and 1985, sheep were gathered and removed from the study area generally between May and November, six to 10 times annually. More intensive
gathering commenced in 1985 (Table 1), with removal throughout the year. The total numbers gathered were used to compute yearly medians (Table 1). Since shepherding effort was not systematic on each gather, not Table 1. The median, minimum and maximum numbers of sheep counted per year in each gather over 607 ha
Year
1983 1984 1985 1986 1987 1988 1989 1990
Number of gathers 10 9 6 22 17 17 17 17
Numbers of sheep per gather Median
Min.
Max.
211 235 261 211 208 131 170 112
101 128 125 34 108 43 46 54
417 368 393 400 373 264 483 366
Vegetation changefollowing reduction in grazing all sheep on the moor will have been removed. The figures therefore provide a relative measure of the reduction in sheep numbers achieved.
Botanical monitoring Monitoring was designed to detect changes in plant cover, available biomass and selected flower production, on the slopes below the plateau, once the sheep control programme had commenced. Because shepherding took place over the whole study area, there were no comparable areas to provide control plots.
Changes in cover Monitoring was concentrated on the patches of partly or completely bare ground, since it was the restoration of these which was the focus of the study. Because these areas were so fragile, fixed transects were adopted rather than random quadrats, to reduce the amount of dispersed trampling and hence avoid damaging the ground unnecessarily during monitoring. Pin frames, which have the additional advantage of providing discrete, objective data, were used in preference to quadrats. Six permanent transects, 10-12 m long, were established in 1983 in various locations on the slope, on representative areas of fragile or patchy bare ground; an additional six transects were added to extend the monitoring in 1984. As two transects could not be relocated during the study, 10 replicate transects were available for comparison between 1984 and 1990. A point frame with 21 pins spaced at 5-cm intervals was placed at right angles to the transect at 1-m intervals, giving 21 × 10-12 pins per transect. All species of higher plant and the presence of bryophytes and lichens touching each pin were recorded. On bare ground, the nature of the substrate (peat, silica or rock) was noted. Monitoring commenced in the spring of 1983, and continued annually at the same season until 1988, by which time the rates of change had declined. Subsequently, monitoring was repeated in 1990. For each transect the total number of hits of each species and for bare ground was calculated and expressed as a percentage frequency (i.e. number of hits as a percentage of the total number of pins per transect). Frequencies in individual transects were then used to compute the mean (+ SD) for all the transects and also for subsets of the transects, located on different parts of the slopes (Fig. 1). The subsets were as follows. Group A (Transects 1, 2 and 3): established within three different locations in a particularly fragile area of bared silica/peat on a steep slope (59%) at the edge of Kinderlow, at c. 530 m, facing north-west. Adjacent vegetation consisted of Nardus and D. flexuosa. Transect 1 could not be relocated from 1987 onwards. Group B (Transects 4, 10, 11 and 12): situated to the north of Kinderlow at 480 m in four locations, all on gently sloping ground (20%) on deeper, peaty podzols, facing north.
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Group C (Transects 5, 6, 7, 8 and 9): above Harry Moor, on a gentle, west-facing slope (20%) at 450 m. Each transect was placed in a bare sheep-hagged area on mineral soil. Transect 7 could not be relocated during the monitoring period.
Reproductive capacity As a means of gauging the regenerative capacity of the main species, the numbers of V. myrtillus flowers and flowering culms of D. flexuosa were counted, generally in 25 0-1-m2 quadrats in May and September respectively. The quadrats were randomly located (but within representative areas of Vaccinium or Deschampsia turf) in the area around the permanent transects. In addition, V. myrtillus flowers were counted, also usually in 25 0.1-m 2 quadrats, on a bank beside Edale Road (Fig. 1), which was the nearest site available as an ungrazed control. However, since this was both at a lower altitude (250 m) and some distance from the Kinder plateau (1.75 km), its use as a control needs to be treated with caution. No equivalent area of ungrazed Deschampsia was available.
Vegetative productivity In order to provide information on the productivity of the site, all the above-ground biomass from selected 0.1m 2 quadrats was removed in the autumn. The sampling area was located randomly within communities near the transects where either D. flexuosa or V. myrtillus was dominant. Any mixed samples were sorted into three components--D, flexuosa, new green growth and old, browner material of Vaccinium--and the dry weights of all the components subsequently determined. In 1983, only five samples from each vegetation type were collected, but results were so variable that sample numbers were increased to 25 from 1985 onwards. From this time, the lightest and heaviest samples collected were discarded and the 10 samples in the middle of the range used to calculate median dry weight. This was necessitated by the lack of resources to sort all the samples.
Statistical methods A one-tailed t-test, using the frequency for each species, was employed to identify significant changes between 1984 (after the extra transects were established) and 1990, except in the Group A transects where there were only two replicates. These were compared using a onetailed Wilcoxon signed rank test. A one-way ANOVA was used to detect significant changes in mean numbers of flower heads per year over the same period. Significant variations in Vaccinium flower counts between the main study area and the ungrazed area on Edale Road were assessed using the t-test for matched pairs. The degree of similarity between the changes in Vaccinium flower counts in the main study area and in the ungrazed area over the study period was compared using Spearman's Rank Correlation. Methods used to select above-ground biomass samples resulted in data unsuited to statistical analysis.
P. Anderson, E. Radford
58 RESULTS
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The vegetation in 1983 Table 2 shows the mean percentage frequency of species in the combined transects, which is taken to represent the general cover of the vegetation. In 1983, prior to full establishment of the sheep control programme, D. flexuosa was clearly the most abundant species, but bare ground was more widespread. However, there is substantial variation between transects (as indicated by the high standard deviation), which partially reflects the heterogeneous environmental conditions. On the very steep, unstable slope (Table 3), Deschampsia only had a mean cover of 30.1% (Group A transects), with a correspondingly higher level of bare ground (64.4%). In contrast, the hagged peaty podzols on more gently sloping ground (Group B transects) supported more vegetation (35% Deschampsia) and slightly less bare ground (58.9%). The lower altitude mineral soils on Harry Moor (Group C transects) were less eroded at the start of the project (27.0% bare), but Deschampsia was still the most abundant species (58.9%). The condition of the Deschampsia turf is reflected better by the productivity than by the transect data (Figs 2 and 3). The very low flowering culm and biomass measurements represented a very closely grazed turf bearing a lawn-like appearance, with few flowering stems. In contrast, the Nardus was largely ungrazed, as is characteristic on such hill land, and contributed patches or tufts throughout the areas of the transects (Table 2). Apart from bryophytes, other species contributed little to the plant community along the transects. However, the presence of Calluna vulgaris in the lower-lying transects (Groups B and C, Table 3) is noteworthy, revealing that even under locally severe grazing pressure very small, regularly decapitated plants can persist for some time. Casual observations on the hill would have concluded that heather was absent around the transect areas, although it was more conspicuous (but rarely flowered) in patches well below the area monitored. The nearest well-managed heather moor lies 2 km to the north-west of the study site.
80
60
40
20
I
t
I
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Fig. 2. Mean numbers (± SD) of Deschampsiaflexuosa flowering culms recorded in randomly located 0.1 m2 quadrats, between 1983 and 1990.
100
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0
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Fig. 3. Changes in the mean above-ground biomass (g dry weight + SD) of Deschampsiaflexuosa turf between 1983 and 1990 in randomly located 0.1 m2 quadrats.
Table 2. Mean percentage frequency (and standard deviation) of species, in all the transects between 1983 and 1990 (no monitoring was undertaken in 1989) 1983 ( n = 6 ) Points without vegetation
Deschampsiaflexuosa Nardusstricta Calluna vulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carexnigra Juncussquarrosus Bryophytes Total
1984(n= 12) 1985(n= 11) 1986(n= 11) 1987(n= 10) 1988(n= 10) 1990(n= 10) Significance
50-98(25-79) 43-06 (23.14) 37.62 (21.69) 40-54(20.52) 46.46(16.31) 55-21 (18.77) 5.36 (6.93) 7.29 (7.93) 8.39 (8.62) 0.37 (0.59) 0-67 (0.87) 1.04 (1.43) 1.38 (1.27) 1.61 (3.71) 2.41 (4.44) 0.36 (0.88) 0-29 (0.80) 0-80 (2.06) 0-79 (1.94) 0-40 (1.39) 0.09 (0.30) 1-67 (4.40) 0-89 (2.42) 0.50 (0-78) 0.16 (0.45) 0.24 (0.50) 4.95 (6.00) 0.57 (0.59) 0.72 (0-83) 105.23
102.20
107.41
28.12 (26.14) 60.45(16-75) 7-24(10.18) 1-20 (5.94) 3.43 (5.94) 0.53 (1.33) 0.30 (0.99) 1.15 (2.62) 0.36 (0-53) 0-50 (0.66) 103.28
24.00 (24.92) 16.58 (21.58) 69.04 (21.54) 71.58 (20.33) 4.26 (5-06) 6.07 (6.13) 4.20 (5.28) 7-20 (8.47) 6.46 (7.27) 11-10(11-04) 0.74 (1.74) 0.87 (1.99) 0.24 (0-95) 0.40 (0.85) 2-14 (4.62) 2.30 (4.87) 0.41 (1-17) 0-67 (1-23) 5.38 (5.15) 12.61 (6.07)
116.87
l-tailed t-test comparing % frequency of the 10 transects in common between 1984 and 1990. *, p<0-05; **,p<0.01; ***, p<0.001.
129.38
8-30 (13.44) 82.99 (11.76) 7.06 (6.86) 16-10 (17-10) 13.65 (12.05) 1-03 (2.31) 0.49 (1.21) 1.86 (3.92) 1.58 (2.18) 13.67 (7.27) 146-73
*** *** ** **
* ***
Vegetation change following reduction in grazing
59
Table 3. Mean percentage frequency (and standard deviation) of species, in the transect groups between 1983 and 1990 (no monitoring was undertaken in 1989) Group A transects (very steep slope), n : 3 1983 Points without vegetation
Deschampsiaflexuosa Aardusstricta (alluna vulgaris Vacciniummyrtillus Eriophorum angustifolium Eriophorum vaginatum (arex nigra Juncussquarrosus Bryophytes
1984
1985
1986"
1987
1988
1990
64.37 (21.25) 64.87 (21.22) 57.70 (25.20) 52.33 (27.30) 61.50 (31.82) 38.10 (48.38) 23.70 (29.84) 30.11 (17.61) 29.26(14.96) 37.05 (20.96) 42.40(19.35) 37.14 (30.73) 53.24 (47.16) 67.53 (21.43) 3.32 (5.75) 4.49 (7.38) 4.91 (7.41) 5.32 (8.87) 0.65 (0-92) 8.23 (0.99) 8.66 (12.25) 0.53 (0.31)
Significance
** *
0.33 (0.29)
1.20 (1.21)
0.59 (0.61)
1-91 (0.86) 11.21 (11.10) 12.20 (10.92)
**
0.56 (0-97) 0-09 (0.16) 2.73 (4.04) 0.69 (0.57)
0.19 (0.33) 0.67 (0.94)
0.54 (0-47) 0.49 (0.62)
2.51 (1.97) 3 . 5 9 (3.49) 0.22 (0.31) 10-42 (3.65) 19.74 (12.87)
**
"One transect lost after 1986 readings. Group B transects (peaty podsols, gentle slope), n = 4 1983h Points without vegetation
Deschampsiaflexuosa Nardusstricta ('allunavulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carex nigra Juncussquarrosus Bryophytes
58.90 35-06 3.46 1.30 0.87 2.17
1984 42.63 45.30 8.37 0.43 3.98 0.22
3.03
1985
(19.80) 35.58 (14.04) (12.26) 54.78 (10.18) (8-70) 9-92 (9.56) (0.83) 0-76 (1-52) (6.18) 4.61 (7.26) (0-44) 0.48 (0.56)
0-40 (0.80) 0.11 (0.22)
0.40 (0.80) 0.90 (1.18)
1986"
1987
1988
28-03(13.54) 23.53 (8-94) 19-70 (7.78) 64.79 (11.04) 70.36 (8.48) 69.08 (7-88) 4.01 (3-24) 5.80 (6.72) 5.75 (5.92) 0.87 (1.74) 1.41 (2.28) 3.03 (4.74) 5-90 (9.86) 7.32 (9-96) 14.37(14.10) 0.40 (0.80) 0.53 (1.06) 0.59 (0.68)
0-59 (0.68) 0.67 (1.02)
0.93 (1.86) 7.09 (7.32)
1986
1987
1990
Significance
6.96 (5.20) 87.42 (5.44) 4-73 (4.46) 8 . 4 4 (9.84) 18.38 (16-86) 0.72 (0.84)
** **
0.11 (0-22) 0.51 (0-76) 15-87 (5-02) 16.02 (4.82)
* *
*
hOne transect only in 1983. Group C transects (steep hagged area on mineral soils), n = 4 1983c Points without vegetation
Deschampsiaflexuosa Nardus stricta Calluna vulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carexnigra Juncus squarrosus Bryophytes
1984
1985c
1988
26.95 58-92 9.38 0.65 2.92
1990
(25.81) 32.35 (24.93) 24.60 (17.64) 16-83(12.28) 9.68 (8.64) 6.08 (4.56) 1.94 (1-72) (21-37) 57.85 (14.44) 69.27(13.54) 69.78(13.54) 83.58 (3.22) 83.25 (4.94) 86.29 (5.72) (11.24) 6.17 (10.13) 9.46 (10-12) 11-90(15.34) 4-51 (4-40) 5.30 (5.32) 8.60 (7-66) (0.76) 1.48 (0-92) 2.11 (1.76) 2.45 (0.22) 9.10 (4.96) 15-00 (7.44) 31.81 (14.00) (0.76) 0.61 (1.10) 1.13 (1.32) 2.21 (1.76) 7.87 (6-46) 7.80 (9-78) 9.65 (7.62) 0-66 (1.48) 1.72 (3-44) 1.06 (2.12) 1.32 (2.64) 1-59 (3.18) 1-85 (3-70) 2.38 (3.37) 1.19 (2.66) 0.24 (0.48) 0.83 (1.66) 0.60 (1.20) 0-86 (l.14) 0.95 0 9 0 ) 1.97 (2.82) 2.46 (3.76) 3.16 (3.74) 5.34 (6.38) 5.75 (6-66) 4.65 (5.38) 0.15 (0-21) 0-12 (0.24) 0,11 (0.22) 0.55 (0.40) 1.65 (2.36) 9.68 (8.98) 0-72 (0.94) 0.58 (0.44) 0.34 (0.22) 6.26 (1.78) 10-44 (7.60) 8.66 (5.88)
Significance * * * *
' Two transects only in 1983, five in 1985. l-tailed Wilcoxon Signed Ranks test between the 1984 and 1990 transects for Group A. 1-tailed t-test comparing 1984 and 1990 for Groups B and C. *, p
Sheep gather numbers T h e n u m b e r o f sheep r e m o v e d f r o m the s t u d y a r e a at a n y o n e t i m e v a r i e d c o n s i d e r a b l y t h r o u g h o u t the sheph e r d i n g p r o g r a m m e . As few as 34 sheep c o u l d be rem o v e d o n o n e o c c a s i o n o r as m a n y as 483, w i t h the a n n u a l m e d i a n n u m b e r p e r g a t h e r r a n g i n g f r o m 112 to 261 ( T a b l e 1). T h e r e was a g e n e r a l d e c l i n i n g t r e n d in these n u m b e r s f r o m 1985 to 1990, w i t h the i n c r e a s e in 1989 p r o b a b l y a t t r i b u t a b l e to a f e r t i l i z a t i o n e x p e r i m e n t o n the hill a d j a c e n t to the s t u d y area. T h e a v e r a g e grazing p r e s s u r e was effectively r e d u c e d f r o m the pre-1982
level o f 2.5 ewes h a ~ to b e t w e e n 0.18 a n d 0.43 ewes ha-~ ( c a l c u l a t e d b y t a k i n g the highest a n d lowest m e d i a n f r o m T a b l e 1 a n d d i v i d i n g b y the a r e a o f the hill).
Changes in plant cover since 1983 The general patterns Deschampsia s h o w s a n e a r l y l i n e a r increase f r o m 1983 to 1990 w h i c h is m i r r o r e d b y a c o n s i s t e n t significant decline in b a r e g r o u n d (Fig. 4(a), T a b l e 2), Vaccinium a n d Calluna s h o w e d a n initial lag effect a n d t h e n ex-
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P. Anderson, E. Radford 100
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•k . . . .
ak.
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~
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1983 1984 1985 1986 1987 1988 1989 1990
1983 1984 1985 1986 1987 1988 1989 1990
(a)
(b)
100
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1988 19841986 1986 1987 1988 1989 1990
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1983 19841985 1986 1987 1988 1989 1990
(c)
(d)
Fig. 4. Changes in mean % frequency (+ SD) ofDeschampsiaflexuosa ( ); bare ground (- - -); Calluna vulgaris (. . . . ), 1983-90. (a) All transects, (b) Group C transects on gentle slope on mineral soils, and (c) Group B transects on gently sloping ground on deeper peaty soils; (d) Group A transects on a steep slope on shallow mineral soils with washed out peat; Nardus stricta (. . . . ). panded more slowly after 1985-86. Vaccinium has spread from the rootstock, with no new plants observed, while established Calluna plants both grew to cover several pin-frame points and spread by seed. The increased height and density of the vegetation is reflected in the total frequency percentages (Table 2) since, as the plants grew and spread, more species hit each pin than in 1983. Recolonisation on the three different slopes Quite striking differences in recolonisation are apparent between the three situations on the hill. The recovery of vegetation in the Group C transects, originally on bared areas on mineral soil, is largely attributable to a significant spread of Deschampsia (from 57.9% to 86.3%), Calluna (from 1.5% to 31.8%) (Fig. 4(b)) and Vaccinium (0-6% to 9.7%), the last two especially since 1986 (Table 3). Calluna plants found in 1990 ranged in size from relatively small seedlings to older plants which flowered in 1988. By 1990, the bare ground had nearly all revegetated (Fig. 4(b)). The changes in other species were not significant (Table 3). In the Group B transects, on gently sloping ground on peaty podzols, the decline in bare ground was also largely attributable to the significant spread of De-
schampsia and, less extensively, to Calluna, Vaccinium
and bryophytes. However, by 1990 there was still a little bare ground (6-96%), (Fig. 4(c)). Only in the Group A transects (on the very steep slope) did the amount of bare ground remain relatively high, although this was restricted to one transect. Deschampsia, Nardus, Vaccinium and bryophytes each increased significantly (Table 3), and spread after 1987 especially, consistent with the decline in bare ground (Fig. 4(d)). Calluna has not colonised these transects, although it is present on the slope nearby. Individual transects
Although plants overall have clearly spread, there have been dramatic but erratic changes in some species in individual transects. The frequency of Calluna, for example, increased from 2.7% in 1984 to 52.4% in 1990 in one of the Group C transects, and from c. 1% originally to 20-30% in three others in this group. Vaccinium spread substantially in two of the Group B transects (from c. 1% originally to 20-42% in 1990) and in one of the Group A transects (from 0-4% to 19.9%) and Nardus now features strongly in one transect from Group A (0% in 1983, 17.3% in 1990). Some species have spread into transects from which they were initially absent,
Vegetation change following reduction in grazing particularly heath rush Juncus squarrosus which was initially present in only two of the original twelve transects, but was found, though at a low frequency, in eight of the ten remaining ones by 1990. Eriophorum angustifolium, Calluna and Vaccinium each spread into one additional transect, whereas other species, such as Eriophorum vaginatum, failed to expand at all.
Changes in productive capacity Deschampsia flexuosa Although each year there was great variability between numbers of flowering culms in individual quadrats, the mean number gradually increased from a very low level in 1983 until 1986, after which there was a substantial increase (Fig. 2). There were significant changes (p < 0.001) in the mean numbers of flower heads during the study period (one-way ANOVA), which reflects increased flowering rather than the spread of Deschampsia, as quadrats were placed over intact swards. Vaccinium myrtillus Mean numbers of Vaccin&m flowers in the transect area were rather low during the first years of sampling (ranging from 0.08 to 1.52) but then began to increase so that by 1988 they were considerably higher (13.36) than in 1986 (1-52). There was then a substantial decline. In comparison, in 1983, flower counts were significantly higher in the ungrazed area on Edale Road (mean 24) than in the main study area (mean 0-08), but they subsequently fell to similar levels to those on the higher slopes in 1985 and 1986. Numbers increased substantially in the ungrazed area in 1987 (mean 33.24) but then declined again in 1988 and further in 1990 (mean 6.68). The variation between both sites is significant (ANOVA p<0.0001). Although the changes on the slope and in the control area appear to be similar since 1986, this was not the case from 1983 to 1986 (Spearman's Rank Correlation, p<0.05). On average, there were more flowers on the control area than on the higher slopes (t-test for matched pairs, p < 0.05).
Changes in vegetative productivity Deschampsia flexuosa Initially, there were small but insignificant changes in the biomass of the Deschampsia turf. After 1988, however, there was a six-fold increase (Fig. 3) in comparison with 1983.
Mixed samples The above-ground biomass of new Vaccinium (1-2 years old) increased markedly from 1983 to 1986, followed by a similar increase in the quantity of old growth. The biomass of the old growth of Vaccinium declined after that date and that of the new growth from 1988 (Fig. 5). The biomass of Deschampsia in these mixed quadrats varied over the whole sampling period, but not consistently. However, a decline in its biomass was observed in 1990 compared with 1988.
61
50
40
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\\ "', \X \ ",
20
10
Fig. 5. Changes in the mean above-ground biomass (g dry weight + SD) of new growth of Vaccinium myrtillus (. . . . . ), old growth of Vaccinium myrtillus (---), and of Deschampsia flexuosa ( - - ) in randomly located 0.1 m: quadrats between 1983 and 1990. DISCUSSION In general, striking changes in plant cover and productivity have been recorded. The only management has been a substantial reduction in levels of sheep grazing; expensive ameliorative treatments (seeding, fertilizer, etc.) have not been used, nor has sheep grazing been removed altogether. A formal experimental control (i.e. maintaining previous levels of grazing on the slopes) was clearly inappropriate, so formal proof that the changes result from control of grazing is lacking. However, the changes match precisely the expectations drawn from other work (Evans, 1977; Tallis & Yalden, 1983). The rate of recolonisation has been fairly slow, commensurate with the high altitude and associated severe environmental conditions experienced on the Kinder Plateau. Moreover, even these rates have been tempered on very steep slopes by the mobility of the substrate. However, even here, only one of the remaining transects displayed a substantial amount of bare ground by 1990. The data suggest that there has generally been a lag between the commencement of sheep gathering and a significant expansion of the dwarf shrubs (Fig. 4(a-d)). Growth of both grasses, particularly Deschampsia, and woody species such as Calluna and Vaccinium, has been favoured by the less intense grazing regime. Deschampsia has spread both vegetatively, to form larger plants, and from new seedlings, which is consistent with the findings of Grime et al. (1988). Young seedlings were seen establishing prolifically each autumn, although not all will have survived subsequent winters, particularly where frost heave occurs on the loose material on the steep slopes. Tallis and Yalden (1983) found a similar pattern on other high-altitude Peak District Moors. However, two relatively mild winters, in 1987-88 and 1988-89, may have enhanced seedling survival in the study area.
62
P. Anderson, E. Radford
The expansion in Vaccinium has been mostly vegetative, with no new plants observed. This is consistent with Ritchie's (1956) view that Vaccinium seeds do not germinate readily in this country and seedlings rarely establish. However, although the frequency of Vaccinium has continued to increase in the transects over the study period, both its biomass and flower production declined after 1988. Competition with Deschampsia could be a cause, but late spring frosts, to which Vaccinium is sensitive (Ritchie, 1956), and the stress of summer drought in 1989 and 1990, could also have affected flowering and productivity. As a reduction in flowers was also observed in the ungrazed area, climatic factors, rather than grazing, seem more likely to be responsible. The success of Calluna on and around the lower transects is a consequence of seedling establishment. Calluna was virtually absent from the area when recording began, so that opportunities for vegetative spread were limited and, in the absence of mature plants, an alternative source of seed must have been available. Calluna produces copious small seeds which may remain dormant in the soil for up to 40 years (Webb, 1986). However, much of the original soil in the sheep-hagged areas had been lost through erosion, and any remaining soil is unlikely to have contained significant amounts of seed, since Calluna had not been an integral part of the plant community for possibly some 40 years (Anderson & Yalden, 1981). Calluna seed is mainly dispersed by wind (Webb, 1986), so seed may have arrived from nearby heather moors (2 km away), or from smaller patches of heather growing near the foot of the slope (0.5 km away at 400 m altitude). It has been suggested that seed may be dispersed up to 0-25 km in winds of 30-40 m s J (Gimingham, 1972). Seed remains in the dead flower capsules and these too can be blown by wind, and may possibly be dispersed by animals. Calluna has so far failed to colonise the particularly fragile, very steep areas along Group A transects, although sporadic plants do occur nearby. Significant quantities of seed may not have reached these areas, but it seems more probable that seedling establishment has not been successful. Other plant species have also been slow to expand or colonise these steep slopes, and this is largely attributed to the instability of the substrate, which is readily dislodged by trampling and grazing, by run-off and by frost heave. In 1990-9l, small numbers of heather seedlings survived in scattered/sheltered locations in the vicinity of these transects; a hopeful indicator of future recovery. A similar expansion of Calluna was witnessed by Hewson (1977), although in his study in North-East England exclosures were used, and the original heather cover was much higher than on the Kinder slopes. The spread of Juncus squarrosus to other areas of the slope is to be expected. It produces large numbers of seeds (up to 10000 m 2). These either germinate in spring or are incorporated into a persistent seed bank, which can establish when sites are later bared by fire or
other disturbances (Grime et al., 1988). However, regeneration by seed is thought to be infrequent in established vegetation, so that as bare areas become fully vegetated its potential for expansion will be much reduced. Nor is it expected that J. squarrosus will subsequently become a more prominent component of the vegetation as it is not competitive under a low grazing pressure. Generally, Nardus stricta, which is regarded as unpalatable to sheep (Jones, 1967), did not respond so well. It is a slow-growing species which is tolerant of stress (Grime et al., 1988) but is unlikely to be able to compete with the more vigorous growth of Deschampsia. Nardus can be an effective colonist of bare ground under favourable conditions when there is a good seed set (King, 1960). However, this may be low in poor summers, particularly at high altitudes. In addition, the seed is not widely dispersed (King, 1960), most seedlings occurring in the immediate vicinity of mature plants. These characteristics would account for the proliferation of Nardus in only one transect on the Kinder slopes rather than throughout the study area. The two Eriophorum species also remained at a fairly constant level. Both produce abundant seed, but seedlings rarely survive, and established plants appear to spread largely by vegetative means (Phillips, 1954; Wein, 1973). However, poor rhizome growth in dry habitats (Phillips, 1954), coupled with low competitive ability, may account for their failure to respond on the drier soils on the steeper slopes in the study area. CONCLUSIONS The study described is a rare example of a long-term project investigating the recovery of damaged and eroding upland vegetation. The results clearly show that where bare ground is patchy on mineral and peaty podzolic soils, plant cover will re-establish if stock grazing levels are reduced from around 2.5 ewes ha ~ to 0.18-0.43 ewes ha ~. However, recolonisation is slow; it has taken eight years for the average plant cover to increase from 49 to 91.7%. On the lower slopes, on mineral soils, 90% vegetation cover was achieved in only five years, whilst on the higher, very steep slopes, 24% of the surface was still bare in 1990. Assuming the same rate of colonisation is maintained, even these steep slopes could be covered within a few more years. They may have been restored more rapidly if stock and people had been completely excluded from the area, but fencing would have been both costly and visually intrusive. Restoration is currently mostly to a Deschampsiadominated sward rather than the Calluna/Vaccinium community described by Moss (1913) 80 years ago. If the regime of low sheep numbers continues in the future, the Deschampsia component is likely to decrease as Calluna and V. myrtillus expand (provided colonisation gaps remain available for new Calluna plants). There are distinct advantages in encouraging a more diverse moorland plant community. Although the De-
Vegetation change following reduction in grazing schampsia is highly favoured by stock in the growing season, Calluna and V. myrtillus both provide valuable forage in autumn and winter when other species are less palatable and digestible. In addition, and of some consequence in the context of the study area, a mixed ericaceous community is more visually attractive, which befits its National Park setting. It also provides a better wildlife habitat appropriate to the Kinder Estate's inclusion in a Site of Special Scientific Interest. ACKNOWLEDGEMENTS Our thanks to the National Trust for permission to monitor on the Kinder Estate and for providing the sheep gathering data. The study was commissioned by the Peak District Moorland Management Project. We are grateful to the Steering Group, the rest of the study team and the anonymous referees for their helpful comments. REFERENCES
Anderson, P. & Yalden, D.W. (1981). Increased sheep numbers and the loss of heather moorland in the Peak District, England. Biol. Conserv., 20, 195 213. Clapham, A.R., Tutin, T.G. & Moore, D.M. (1987). Flora of the British Isles. Cambridge University Press, Cambridge. Evans, R. (1977). Overgrazing and soil erosion on hill pas-
63
tures with particular reference to the Peak District. J. Brit. Grassl. Soc., 32, 65-76. Grime, J.P. (1979). Plant strategies and vegetation processes. Wiley, Chichester. Grime, J.P., Hodgson, J.G. & Hunt, R. (1988). Comparative plant ecology a functional approach to common British species. Unwin Hyman, London. Gimingham, C.H. (1972). Ecology ofheathlands. Chapman & Hall, London. Hewson, R. (1977). The effects on heather Calluna vulgaris of excluding sheep from moorland in North-East England. Naturalist, 102, 133 6. Jones, Li. I. (1967). Studies of hill land in Wales. Welsh Plant Breeding Station, Aberystwyth, Tech. Bull., No. 2. King, J. (1960). Observations on the seedling establishment and growth of Nardus stricta in burned Callunetum. J Ecol., 48, 667 77. Moss, C.E. (1913). The vegetation of the Peak District. Cambridge University Press, Cambridge. Phillips, J., Yalden, D.W. & Tallis, J. (1981). Peak District moorland erosion stud)' Phase I report. Peak Park Joint Planning Board, Bakewell, Derbyshire. Phillips, M.E. (1954). Biological flora of the British Isles: Eriophorum angustifolium Roth. J. Ecol., 42, 612-22. Ritchie, J.C. (1956). Biological flora of the British Isles: Vaccinium myrtillus L. J. Ecol., 44, 291--99. Tallis, J.H. & Yalden, D.W. (1983). Peak District moorland restoration project Phase 2 report. Re-vegetation trials. Peak Park Joint Planning Board, Bakewell, Derbyshire. Webb, N. (1986). Heathlands. Collins, London. Wein, R.W. (1973). Biological flora of the British Isles: Eriphorum vaginatum L. J. Ecol., 61,601 15.
CHANGES IN VEGETATION FOLLOWING REDUCTION IN GRAZING PRESSURE ON THE NATIONAL TRUST'S KINDER ESTATE, PEAK DISTRICT, DERBYSHIRE, ENGLAND Penny Anderson & Elaine Radford Penny Anderson Associates, 52 Lower Lane, Chinley, Stockport, UK, SK12 6BD (Received 26 October 1992; revised version received 25 August 1993; accepted 1 September 1993)
plateau had been mapped by the Peak District's Moorland Erosion Project as fragile and eroding (Phillips et al., 1981). The 10-km grid square (SK08) in which the majority of Kinder lies contributed 1.78 km 2 to the 33.25 km 2 of eroded or partially eroded ground estimated by the study in the Peak District National Park. Most of the erosion in the moorlands as a whole was attributed to fire damage, but on the slopes west of Kinder both the vegetation change and the soil erosion resulted mostly from poorly controlled sheep grazing (Phillips et al., 1981).
Abstract A monitoring programme is described which charts the recolonisation of moorland vegetation on the slopes of the Kinder plateau (Peak District, Derbyshire, UK) after reduction of sheep grazing. Deschampsia flexuosa has spread substantially, and there have been parallel increases in biomass and numbers of flowering culms. Calluna vulgaris and Vaccinium myrtillus have also increased significantly, but changes in other moorland species were limited. The previously bare and eroding ground has largely been revegetated except on the steepest slope, and the community is reverting to that described for the area in 1913.
Sheep grazing pressure The Kinder Estate was purchased by the National Trust in 1982, and part of the Trust's management plan was to reduce sheep numbers on the moorland with the objective of encouraging recovery of the vegetation in areas that were fragile or eroding. More than 1500 sheep regularly grazed the 607 ha of these moors at this time (an average of 2.5 ewes ha-l). Given the recommended moorland grazing level of 1 ewe ha ~ (Phillips et al., 1981), this represents a high concentration of animals, bearing in mind the small proportion of more palatable and nutritious vegetation and the extent of bare ground. It was clear that the grazing pressure was concentrated for much of the year on the slopes below the plateau where some shelter was afforded from strong winds and rain, and where preferred species were concentrated. As a result, the vegetation cover was fragmenting and soils beginning to erode. The previous owners had attempted to reduce the grazing pressure by removing most of their sheep, and the majority still on the moor were trespassers from adjoining areas. This ingress was effectively reduced by the National Trust after 1982 by regularly gathering sheep and penning them to await collection by their owners. At the time, this was seen as a radical and controversial change in management, although revegetation trials had indicated the value of excluding grazing, amongst other treatments (Tallis & Yalden, 1983). Since there were few examples of long-term monitoring of the effects on vegetation of such a reduction in grazing, the Peak District Moorland Management Project
Keywords: Peak District, moorland, heather, grazing, restoration.
INTRODUCTION The nature of the site The Kinder Estate (1267 ha) lies within the moorland zone of the Peak District National Park (Fig. 1) and comprises part of the high plateau of Kinder Scout (at c. 635 m altitude) which is covered in blanket peat, flanked by steeper slopes bearing mineral soils and peaty podzols. The extensively eroded peat haggs and groughs (the dissected peat mounds and channels) of the plateau support fragmented communities of the cotton-grasses Eriophorum vaginatum and E. angustifolium, bilberry Vaccinium myrtillus and crowberry Empetrum nigrum. There is much bare peat and, in places, the underlying regolith is now exposed, and has been only superficially colonised by scattered moorland plants including wavy hair-grass Deschampsia flexuosa and mat-grass Nardus stricta. In 1982, the western slopes below the plateau were mostly covered by a discontinuous D. flexuosa turf intermingled with patches of N. stricta, V. myrtillus and bare ground. The state of the slopes at this time contrasted markedly with the situation in 1913 when they were mapped by Moss (1913) as a Vaccinium myrtillus/ Calluna vulgaris community. In 1979, the whole of the west side of the Kinder 55
P. Anderson, E. Radford
56
~
~ Manchest:~ r'l Osheffield
Kinder
Kinder OKi Endnderl°w ) / l/ LOw
l
B A J[
A
N 0 I,
1 I
2 l
Scale (kin)
Fig. 1, The location of the groups of transects (O A, B and C) within the National Trust's Kinder Estate ( - - Estate boundary) and Edale Road bank (&) on which Vaccinium myrtillus flowers were counted. Contours shown - - 550 and 600 m. Inset shows the general location of Kinder. (which had evolved from the Moorland Erosion Study) commissioned the present study. Its principal objective was to monitor the effectiveness of shepherding as a means of securing revegetation of eroding ground without the expense of fencing, or supplementary treatment with seed or fertilizers. This would enable the Moorland Management Project to demonstrate the effects and value of such a change in management tO other land managers. Plant names follow those used in Clapham et al. (1987). METHODS Sheep control programme
Between 1983 and 1985, sheep were gathered and removed from the study area generally between May and November, six to 10 times annually. More intensive
gathering commenced in 1985 (Table 1), with removal throughout the year. The total numbers gathered were used to compute yearly medians (Table 1). Since shepherding effort was not systematic on each gather, not Table 1. The median, minimum and maximum numbers of sheep counted per year in each gather over 607 ha
Year
1983 1984 1985 1986 1987 1988 1989 1990
Number of gathers 10 9 6 22 17 17 17 17
Numbers of sheep per gather Median
Min.
Max.
211 235 261 211 208 131 170 112
101 128 125 34 108 43 46 54
417 368 393 400 373 264 483 366
Vegetation changefollowing reduction in grazing all sheep on the moor will have been removed. The figures therefore provide a relative measure of the reduction in sheep numbers achieved.
Botanical monitoring Monitoring was designed to detect changes in plant cover, available biomass and selected flower production, on the slopes below the plateau, once the sheep control programme had commenced. Because shepherding took place over the whole study area, there were no comparable areas to provide control plots.
Changes in cover Monitoring was concentrated on the patches of partly or completely bare ground, since it was the restoration of these which was the focus of the study. Because these areas were so fragile, fixed transects were adopted rather than random quadrats, to reduce the amount of dispersed trampling and hence avoid damaging the ground unnecessarily during monitoring. Pin frames, which have the additional advantage of providing discrete, objective data, were used in preference to quadrats. Six permanent transects, 10-12 m long, were established in 1983 in various locations on the slope, on representative areas of fragile or patchy bare ground; an additional six transects were added to extend the monitoring in 1984. As two transects could not be relocated during the study, 10 replicate transects were available for comparison between 1984 and 1990. A point frame with 21 pins spaced at 5-cm intervals was placed at right angles to the transect at 1-m intervals, giving 21 × 10-12 pins per transect. All species of higher plant and the presence of bryophytes and lichens touching each pin were recorded. On bare ground, the nature of the substrate (peat, silica or rock) was noted. Monitoring commenced in the spring of 1983, and continued annually at the same season until 1988, by which time the rates of change had declined. Subsequently, monitoring was repeated in 1990. For each transect the total number of hits of each species and for bare ground was calculated and expressed as a percentage frequency (i.e. number of hits as a percentage of the total number of pins per transect). Frequencies in individual transects were then used to compute the mean (+ SD) for all the transects and also for subsets of the transects, located on different parts of the slopes (Fig. 1). The subsets were as follows. Group A (Transects 1, 2 and 3): established within three different locations in a particularly fragile area of bared silica/peat on a steep slope (59%) at the edge of Kinderlow, at c. 530 m, facing north-west. Adjacent vegetation consisted of Nardus and D. flexuosa. Transect 1 could not be relocated from 1987 onwards. Group B (Transects 4, 10, 11 and 12): situated to the north of Kinderlow at 480 m in four locations, all on gently sloping ground (20%) on deeper, peaty podzols, facing north.
57
Group C (Transects 5, 6, 7, 8 and 9): above Harry Moor, on a gentle, west-facing slope (20%) at 450 m. Each transect was placed in a bare sheep-hagged area on mineral soil. Transect 7 could not be relocated during the monitoring period.
Reproductive capacity As a means of gauging the regenerative capacity of the main species, the numbers of V. myrtillus flowers and flowering culms of D. flexuosa were counted, generally in 25 0-1-m2 quadrats in May and September respectively. The quadrats were randomly located (but within representative areas of Vaccinium or Deschampsia turf) in the area around the permanent transects. In addition, V. myrtillus flowers were counted, also usually in 25 0.1-m 2 quadrats, on a bank beside Edale Road (Fig. 1), which was the nearest site available as an ungrazed control. However, since this was both at a lower altitude (250 m) and some distance from the Kinder plateau (1.75 km), its use as a control needs to be treated with caution. No equivalent area of ungrazed Deschampsia was available.
Vegetative productivity In order to provide information on the productivity of the site, all the above-ground biomass from selected 0.1m 2 quadrats was removed in the autumn. The sampling area was located randomly within communities near the transects where either D. flexuosa or V. myrtillus was dominant. Any mixed samples were sorted into three components--D, flexuosa, new green growth and old, browner material of Vaccinium--and the dry weights of all the components subsequently determined. In 1983, only five samples from each vegetation type were collected, but results were so variable that sample numbers were increased to 25 from 1985 onwards. From this time, the lightest and heaviest samples collected were discarded and the 10 samples in the middle of the range used to calculate median dry weight. This was necessitated by the lack of resources to sort all the samples.
Statistical methods A one-tailed t-test, using the frequency for each species, was employed to identify significant changes between 1984 (after the extra transects were established) and 1990, except in the Group A transects where there were only two replicates. These were compared using a onetailed Wilcoxon signed rank test. A one-way ANOVA was used to detect significant changes in mean numbers of flower heads per year over the same period. Significant variations in Vaccinium flower counts between the main study area and the ungrazed area on Edale Road were assessed using the t-test for matched pairs. The degree of similarity between the changes in Vaccinium flower counts in the main study area and in the ungrazed area over the study period was compared using Spearman's Rank Correlation. Methods used to select above-ground biomass samples resulted in data unsuited to statistical analysis.
P. Anderson, E. Radford
58 RESULTS
100
The vegetation in 1983 Table 2 shows the mean percentage frequency of species in the combined transects, which is taken to represent the general cover of the vegetation. In 1983, prior to full establishment of the sheep control programme, D. flexuosa was clearly the most abundant species, but bare ground was more widespread. However, there is substantial variation between transects (as indicated by the high standard deviation), which partially reflects the heterogeneous environmental conditions. On the very steep, unstable slope (Table 3), Deschampsia only had a mean cover of 30.1% (Group A transects), with a correspondingly higher level of bare ground (64.4%). In contrast, the hagged peaty podzols on more gently sloping ground (Group B transects) supported more vegetation (35% Deschampsia) and slightly less bare ground (58.9%). The lower altitude mineral soils on Harry Moor (Group C transects) were less eroded at the start of the project (27.0% bare), but Deschampsia was still the most abundant species (58.9%). The condition of the Deschampsia turf is reflected better by the productivity than by the transect data (Figs 2 and 3). The very low flowering culm and biomass measurements represented a very closely grazed turf bearing a lawn-like appearance, with few flowering stems. In contrast, the Nardus was largely ungrazed, as is characteristic on such hill land, and contributed patches or tufts throughout the areas of the transects (Table 2). Apart from bryophytes, other species contributed little to the plant community along the transects. However, the presence of Calluna vulgaris in the lower-lying transects (Groups B and C, Table 3) is noteworthy, revealing that even under locally severe grazing pressure very small, regularly decapitated plants can persist for some time. Casual observations on the hill would have concluded that heather was absent around the transect areas, although it was more conspicuous (but rarely flowered) in patches well below the area monitored. The nearest well-managed heather moor lies 2 km to the north-west of the study site.
80
60
40
20
I
t
I
I
I
I
I
I
Fig. 2. Mean numbers (± SD) of Deschampsiaflexuosa flowering culms recorded in randomly located 0.1 m2 quadrats, between 1983 and 1990.
100
8O
60
20
0
I
I
I
I
I
I
I
I
Fig. 3. Changes in the mean above-ground biomass (g dry weight + SD) of Deschampsiaflexuosa turf between 1983 and 1990 in randomly located 0.1 m2 quadrats.
Table 2. Mean percentage frequency (and standard deviation) of species, in all the transects between 1983 and 1990 (no monitoring was undertaken in 1989) 1983 ( n = 6 ) Points without vegetation
Deschampsiaflexuosa Nardusstricta Calluna vulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carexnigra Juncussquarrosus Bryophytes Total
1984(n= 12) 1985(n= 11) 1986(n= 11) 1987(n= 10) 1988(n= 10) 1990(n= 10) Significance
50-98(25-79) 43-06 (23.14) 37.62 (21.69) 40-54(20.52) 46.46(16.31) 55-21 (18.77) 5.36 (6.93) 7.29 (7.93) 8.39 (8.62) 0.37 (0.59) 0-67 (0.87) 1.04 (1.43) 1.38 (1.27) 1.61 (3.71) 2.41 (4.44) 0.36 (0.88) 0-29 (0.80) 0-80 (2.06) 0-79 (1.94) 0-40 (1.39) 0.09 (0.30) 1-67 (4.40) 0-89 (2.42) 0.50 (0-78) 0.16 (0.45) 0.24 (0.50) 4.95 (6.00) 0.57 (0.59) 0.72 (0-83) 105.23
102.20
107.41
28.12 (26.14) 60.45(16-75) 7-24(10.18) 1-20 (5.94) 3.43 (5.94) 0.53 (1.33) 0.30 (0.99) 1.15 (2.62) 0.36 (0-53) 0-50 (0.66) 103.28
24.00 (24.92) 16.58 (21.58) 69.04 (21.54) 71.58 (20.33) 4.26 (5-06) 6.07 (6.13) 4.20 (5.28) 7-20 (8.47) 6.46 (7.27) 11-10(11-04) 0.74 (1.74) 0.87 (1.99) 0.24 (0-95) 0.40 (0.85) 2-14 (4.62) 2.30 (4.87) 0.41 (1-17) 0-67 (1-23) 5.38 (5.15) 12.61 (6.07)
116.87
l-tailed t-test comparing % frequency of the 10 transects in common between 1984 and 1990. *, p<0-05; **,p<0.01; ***, p<0.001.
129.38
8-30 (13.44) 82.99 (11.76) 7.06 (6.86) 16-10 (17-10) 13.65 (12.05) 1-03 (2.31) 0.49 (1.21) 1.86 (3.92) 1.58 (2.18) 13.67 (7.27) 146-73
*** *** ** **
* ***
Vegetation change following reduction in grazing
59
Table 3. Mean percentage frequency (and standard deviation) of species, in the transect groups between 1983 and 1990 (no monitoring was undertaken in 1989) Group A transects (very steep slope), n : 3 1983 Points without vegetation
Deschampsiaflexuosa Aardusstricta (alluna vulgaris Vacciniummyrtillus Eriophorum angustifolium Eriophorum vaginatum (arex nigra Juncussquarrosus Bryophytes
1984
1985
1986"
1987
1988
1990
64.37 (21.25) 64.87 (21.22) 57.70 (25.20) 52.33 (27.30) 61.50 (31.82) 38.10 (48.38) 23.70 (29.84) 30.11 (17.61) 29.26(14.96) 37.05 (20.96) 42.40(19.35) 37.14 (30.73) 53.24 (47.16) 67.53 (21.43) 3.32 (5.75) 4.49 (7.38) 4.91 (7.41) 5.32 (8.87) 0.65 (0-92) 8.23 (0.99) 8.66 (12.25) 0.53 (0.31)
Significance
** *
0.33 (0.29)
1.20 (1.21)
0.59 (0.61)
1-91 (0.86) 11.21 (11.10) 12.20 (10.92)
**
0.56 (0-97) 0-09 (0.16) 2.73 (4.04) 0.69 (0.57)
0.19 (0.33) 0.67 (0.94)
0.54 (0-47) 0.49 (0.62)
2.51 (1.97) 3 . 5 9 (3.49) 0.22 (0.31) 10-42 (3.65) 19.74 (12.87)
**
"One transect lost after 1986 readings. Group B transects (peaty podsols, gentle slope), n = 4 1983h Points without vegetation
Deschampsiaflexuosa Nardusstricta ('allunavulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carex nigra Juncussquarrosus Bryophytes
58.90 35-06 3.46 1.30 0.87 2.17
1984 42.63 45.30 8.37 0.43 3.98 0.22
3.03
1985
(19.80) 35.58 (14.04) (12.26) 54.78 (10.18) (8-70) 9-92 (9.56) (0.83) 0-76 (1-52) (6.18) 4.61 (7.26) (0-44) 0.48 (0.56)
0-40 (0.80) 0.11 (0.22)
0.40 (0.80) 0.90 (1.18)
1986"
1987
1988
28-03(13.54) 23.53 (8-94) 19-70 (7.78) 64.79 (11.04) 70.36 (8.48) 69.08 (7-88) 4.01 (3-24) 5.80 (6.72) 5.75 (5.92) 0.87 (1.74) 1.41 (2.28) 3.03 (4.74) 5-90 (9.86) 7.32 (9-96) 14.37(14.10) 0.40 (0.80) 0.53 (1.06) 0.59 (0.68)
0-59 (0.68) 0.67 (1.02)
0.93 (1.86) 7.09 (7.32)
1986
1987
1990
Significance
6.96 (5.20) 87.42 (5.44) 4-73 (4.46) 8 . 4 4 (9.84) 18.38 (16-86) 0.72 (0.84)
** **
0.11 (0-22) 0.51 (0-76) 15-87 (5-02) 16.02 (4.82)
* *
*
hOne transect only in 1983. Group C transects (steep hagged area on mineral soils), n = 4 1983c Points without vegetation
Deschampsiaflexuosa Nardus stricta Calluna vulgaris Vacciniummyrtillus Eriophorumangustifolium Eriophorum vaginatum Carexnigra Juncus squarrosus Bryophytes
1984
1985c
1988
26.95 58-92 9.38 0.65 2.92
1990
(25.81) 32.35 (24.93) 24.60 (17.64) 16-83(12.28) 9.68 (8.64) 6.08 (4.56) 1.94 (1-72) (21-37) 57.85 (14.44) 69.27(13.54) 69.78(13.54) 83.58 (3.22) 83.25 (4.94) 86.29 (5.72) (11.24) 6.17 (10.13) 9.46 (10-12) 11-90(15.34) 4-51 (4-40) 5.30 (5.32) 8.60 (7-66) (0.76) 1.48 (0-92) 2.11 (1.76) 2.45 (0.22) 9.10 (4.96) 15-00 (7.44) 31.81 (14.00) (0.76) 0.61 (1.10) 1.13 (1.32) 2.21 (1.76) 7.87 (6-46) 7.80 (9-78) 9.65 (7.62) 0-66 (1.48) 1.72 (3-44) 1.06 (2.12) 1.32 (2.64) 1-59 (3.18) 1-85 (3-70) 2.38 (3.37) 1.19 (2.66) 0.24 (0.48) 0.83 (1.66) 0.60 (1.20) 0-86 (l.14) 0.95 0 9 0 ) 1.97 (2.82) 2.46 (3.76) 3.16 (3.74) 5.34 (6.38) 5.75 (6-66) 4.65 (5.38) 0.15 (0-21) 0-12 (0.24) 0,11 (0.22) 0.55 (0.40) 1.65 (2.36) 9.68 (8.98) 0-72 (0.94) 0.58 (0.44) 0.34 (0.22) 6.26 (1.78) 10-44 (7.60) 8.66 (5.88)
Significance * * * *
' Two transects only in 1983, five in 1985. l-tailed Wilcoxon Signed Ranks test between the 1984 and 1990 transects for Group A. 1-tailed t-test comparing 1984 and 1990 for Groups B and C. *, p
Sheep gather numbers T h e n u m b e r o f sheep r e m o v e d f r o m the s t u d y a r e a at a n y o n e t i m e v a r i e d c o n s i d e r a b l y t h r o u g h o u t the sheph e r d i n g p r o g r a m m e . As few as 34 sheep c o u l d be rem o v e d o n o n e o c c a s i o n o r as m a n y as 483, w i t h the a n n u a l m e d i a n n u m b e r p e r g a t h e r r a n g i n g f r o m 112 to 261 ( T a b l e 1). T h e r e was a g e n e r a l d e c l i n i n g t r e n d in these n u m b e r s f r o m 1985 to 1990, w i t h the i n c r e a s e in 1989 p r o b a b l y a t t r i b u t a b l e to a f e r t i l i z a t i o n e x p e r i m e n t o n the hill a d j a c e n t to the s t u d y area. T h e a v e r a g e grazing p r e s s u r e was effectively r e d u c e d f r o m the pre-1982
level o f 2.5 ewes h a ~ to b e t w e e n 0.18 a n d 0.43 ewes ha-~ ( c a l c u l a t e d b y t a k i n g the highest a n d lowest m e d i a n f r o m T a b l e 1 a n d d i v i d i n g b y the a r e a o f the hill).
Changes in plant cover since 1983 The general patterns Deschampsia s h o w s a n e a r l y l i n e a r increase f r o m 1983 to 1990 w h i c h is m i r r o r e d b y a c o n s i s t e n t significant decline in b a r e g r o u n d (Fig. 4(a), T a b l e 2), Vaccinium a n d Calluna s h o w e d a n initial lag effect a n d t h e n ex-
60
P. Anderson, E. Radford 100
100
80
80
60
60
40
40
20
20
•k . . . .
ak.
. . . .
~
. . . . .
1983 1984 1985 1986 1987 1988 1989 1990
1983 1984 1985 1986 1987 1988 1989 1990
(a)
(b)
100
100
80
80
60
r i
Nxx
.t
60
40
4O
20
I
1988 19841986 1986 1987 1988 1989 1990
i
0
1983 19841985 1986 1987 1988 1989 1990
(c)
(d)
Fig. 4. Changes in mean % frequency (+ SD) ofDeschampsiaflexuosa ( ); bare ground (- - -); Calluna vulgaris (. . . . ), 1983-90. (a) All transects, (b) Group C transects on gentle slope on mineral soils, and (c) Group B transects on gently sloping ground on deeper peaty soils; (d) Group A transects on a steep slope on shallow mineral soils with washed out peat; Nardus stricta (. . . . ). panded more slowly after 1985-86. Vaccinium has spread from the rootstock, with no new plants observed, while established Calluna plants both grew to cover several pin-frame points and spread by seed. The increased height and density of the vegetation is reflected in the total frequency percentages (Table 2) since, as the plants grew and spread, more species hit each pin than in 1983. Recolonisation on the three different slopes Quite striking differences in recolonisation are apparent between the three situations on the hill. The recovery of vegetation in the Group C transects, originally on bared areas on mineral soil, is largely attributable to a significant spread of Deschampsia (from 57.9% to 86.3%), Calluna (from 1.5% to 31.8%) (Fig. 4(b)) and Vaccinium (0-6% to 9.7%), the last two especially since 1986 (Table 3). Calluna plants found in 1990 ranged in size from relatively small seedlings to older plants which flowered in 1988. By 1990, the bare ground had nearly all revegetated (Fig. 4(b)). The changes in other species were not significant (Table 3). In the Group B transects, on gently sloping ground on peaty podzols, the decline in bare ground was also largely attributable to the significant spread of De-
schampsia and, less extensively, to Calluna, Vaccinium
and bryophytes. However, by 1990 there was still a little bare ground (6-96%), (Fig. 4(c)). Only in the Group A transects (on the very steep slope) did the amount of bare ground remain relatively high, although this was restricted to one transect. Deschampsia, Nardus, Vaccinium and bryophytes each increased significantly (Table 3), and spread after 1987 especially, consistent with the decline in bare ground (Fig. 4(d)). Calluna has not colonised these transects, although it is present on the slope nearby. Individual transects
Although plants overall have clearly spread, there have been dramatic but erratic changes in some species in individual transects. The frequency of Calluna, for example, increased from 2.7% in 1984 to 52.4% in 1990 in one of the Group C transects, and from c. 1% originally to 20-30% in three others in this group. Vaccinium spread substantially in two of the Group B transects (from c. 1% originally to 20-42% in 1990) and in one of the Group A transects (from 0-4% to 19.9%) and Nardus now features strongly in one transect from Group A (0% in 1983, 17.3% in 1990). Some species have spread into transects from which they were initially absent,
Vegetation change following reduction in grazing particularly heath rush Juncus squarrosus which was initially present in only two of the original twelve transects, but was found, though at a low frequency, in eight of the ten remaining ones by 1990. Eriophorum angustifolium, Calluna and Vaccinium each spread into one additional transect, whereas other species, such as Eriophorum vaginatum, failed to expand at all.
Changes in productive capacity Deschampsia flexuosa Although each year there was great variability between numbers of flowering culms in individual quadrats, the mean number gradually increased from a very low level in 1983 until 1986, after which there was a substantial increase (Fig. 2). There were significant changes (p < 0.001) in the mean numbers of flower heads during the study period (one-way ANOVA), which reflects increased flowering rather than the spread of Deschampsia, as quadrats were placed over intact swards. Vaccinium myrtillus Mean numbers of Vaccin&m flowers in the transect area were rather low during the first years of sampling (ranging from 0.08 to 1.52) but then began to increase so that by 1988 they were considerably higher (13.36) than in 1986 (1-52). There was then a substantial decline. In comparison, in 1983, flower counts were significantly higher in the ungrazed area on Edale Road (mean 24) than in the main study area (mean 0-08), but they subsequently fell to similar levels to those on the higher slopes in 1985 and 1986. Numbers increased substantially in the ungrazed area in 1987 (mean 33.24) but then declined again in 1988 and further in 1990 (mean 6.68). The variation between both sites is significant (ANOVA p<0.0001). Although the changes on the slope and in the control area appear to be similar since 1986, this was not the case from 1983 to 1986 (Spearman's Rank Correlation, p<0.05). On average, there were more flowers on the control area than on the higher slopes (t-test for matched pairs, p < 0.05).
Changes in vegetative productivity Deschampsia flexuosa Initially, there were small but insignificant changes in the biomass of the Deschampsia turf. After 1988, however, there was a six-fold increase (Fig. 3) in comparison with 1983.
Mixed samples The above-ground biomass of new Vaccinium (1-2 years old) increased markedly from 1983 to 1986, followed by a similar increase in the quantity of old growth. The biomass of the old growth of Vaccinium declined after that date and that of the new growth from 1988 (Fig. 5). The biomass of Deschampsia in these mixed quadrats varied over the whole sampling period, but not consistently. However, a decline in its biomass was observed in 1990 compared with 1988.
61
50
40
I /,, 30
,,"
\\ "', \X \ ",
20
10
Fig. 5. Changes in the mean above-ground biomass (g dry weight + SD) of new growth of Vaccinium myrtillus (. . . . . ), old growth of Vaccinium myrtillus (---), and of Deschampsia flexuosa ( - - ) in randomly located 0.1 m: quadrats between 1983 and 1990. DISCUSSION In general, striking changes in plant cover and productivity have been recorded. The only management has been a substantial reduction in levels of sheep grazing; expensive ameliorative treatments (seeding, fertilizer, etc.) have not been used, nor has sheep grazing been removed altogether. A formal experimental control (i.e. maintaining previous levels of grazing on the slopes) was clearly inappropriate, so formal proof that the changes result from control of grazing is lacking. However, the changes match precisely the expectations drawn from other work (Evans, 1977; Tallis & Yalden, 1983). The rate of recolonisation has been fairly slow, commensurate with the high altitude and associated severe environmental conditions experienced on the Kinder Plateau. Moreover, even these rates have been tempered on very steep slopes by the mobility of the substrate. However, even here, only one of the remaining transects displayed a substantial amount of bare ground by 1990. The data suggest that there has generally been a lag between the commencement of sheep gathering and a significant expansion of the dwarf shrubs (Fig. 4(a-d)). Growth of both grasses, particularly Deschampsia, and woody species such as Calluna and Vaccinium, has been favoured by the less intense grazing regime. Deschampsia has spread both vegetatively, to form larger plants, and from new seedlings, which is consistent with the findings of Grime et al. (1988). Young seedlings were seen establishing prolifically each autumn, although not all will have survived subsequent winters, particularly where frost heave occurs on the loose material on the steep slopes. Tallis and Yalden (1983) found a similar pattern on other high-altitude Peak District Moors. However, two relatively mild winters, in 1987-88 and 1988-89, may have enhanced seedling survival in the study area.
62
P. Anderson, E. Radford
The expansion in Vaccinium has been mostly vegetative, with no new plants observed. This is consistent with Ritchie's (1956) view that Vaccinium seeds do not germinate readily in this country and seedlings rarely establish. However, although the frequency of Vaccinium has continued to increase in the transects over the study period, both its biomass and flower production declined after 1988. Competition with Deschampsia could be a cause, but late spring frosts, to which Vaccinium is sensitive (Ritchie, 1956), and the stress of summer drought in 1989 and 1990, could also have affected flowering and productivity. As a reduction in flowers was also observed in the ungrazed area, climatic factors, rather than grazing, seem more likely to be responsible. The success of Calluna on and around the lower transects is a consequence of seedling establishment. Calluna was virtually absent from the area when recording began, so that opportunities for vegetative spread were limited and, in the absence of mature plants, an alternative source of seed must have been available. Calluna produces copious small seeds which may remain dormant in the soil for up to 40 years (Webb, 1986). However, much of the original soil in the sheep-hagged areas had been lost through erosion, and any remaining soil is unlikely to have contained significant amounts of seed, since Calluna had not been an integral part of the plant community for possibly some 40 years (Anderson & Yalden, 1981). Calluna seed is mainly dispersed by wind (Webb, 1986), so seed may have arrived from nearby heather moors (2 km away), or from smaller patches of heather growing near the foot of the slope (0.5 km away at 400 m altitude). It has been suggested that seed may be dispersed up to 0-25 km in winds of 30-40 m s J (Gimingham, 1972). Seed remains in the dead flower capsules and these too can be blown by wind, and may possibly be dispersed by animals. Calluna has so far failed to colonise the particularly fragile, very steep areas along Group A transects, although sporadic plants do occur nearby. Significant quantities of seed may not have reached these areas, but it seems more probable that seedling establishment has not been successful. Other plant species have also been slow to expand or colonise these steep slopes, and this is largely attributed to the instability of the substrate, which is readily dislodged by trampling and grazing, by run-off and by frost heave. In 1990-9l, small numbers of heather seedlings survived in scattered/sheltered locations in the vicinity of these transects; a hopeful indicator of future recovery. A similar expansion of Calluna was witnessed by Hewson (1977), although in his study in North-East England exclosures were used, and the original heather cover was much higher than on the Kinder slopes. The spread of Juncus squarrosus to other areas of the slope is to be expected. It produces large numbers of seeds (up to 10000 m 2). These either germinate in spring or are incorporated into a persistent seed bank, which can establish when sites are later bared by fire or
other disturbances (Grime et al., 1988). However, regeneration by seed is thought to be infrequent in established vegetation, so that as bare areas become fully vegetated its potential for expansion will be much reduced. Nor is it expected that J. squarrosus will subsequently become a more prominent component of the vegetation as it is not competitive under a low grazing pressure. Generally, Nardus stricta, which is regarded as unpalatable to sheep (Jones, 1967), did not respond so well. It is a slow-growing species which is tolerant of stress (Grime et al., 1988) but is unlikely to be able to compete with the more vigorous growth of Deschampsia. Nardus can be an effective colonist of bare ground under favourable conditions when there is a good seed set (King, 1960). However, this may be low in poor summers, particularly at high altitudes. In addition, the seed is not widely dispersed (King, 1960), most seedlings occurring in the immediate vicinity of mature plants. These characteristics would account for the proliferation of Nardus in only one transect on the Kinder slopes rather than throughout the study area. The two Eriophorum species also remained at a fairly constant level. Both produce abundant seed, but seedlings rarely survive, and established plants appear to spread largely by vegetative means (Phillips, 1954; Wein, 1973). However, poor rhizome growth in dry habitats (Phillips, 1954), coupled with low competitive ability, may account for their failure to respond on the drier soils on the steeper slopes in the study area. CONCLUSIONS The study described is a rare example of a long-term project investigating the recovery of damaged and eroding upland vegetation. The results clearly show that where bare ground is patchy on mineral and peaty podzolic soils, plant cover will re-establish if stock grazing levels are reduced from around 2.5 ewes ha ~ to 0.18-0.43 ewes ha ~. However, recolonisation is slow; it has taken eight years for the average plant cover to increase from 49 to 91.7%. On the lower slopes, on mineral soils, 90% vegetation cover was achieved in only five years, whilst on the higher, very steep slopes, 24% of the surface was still bare in 1990. Assuming the same rate of colonisation is maintained, even these steep slopes could be covered within a few more years. They may have been restored more rapidly if stock and people had been completely excluded from the area, but fencing would have been both costly and visually intrusive. Restoration is currently mostly to a Deschampsiadominated sward rather than the Calluna/Vaccinium community described by Moss (1913) 80 years ago. If the regime of low sheep numbers continues in the future, the Deschampsia component is likely to decrease as Calluna and V. myrtillus expand (provided colonisation gaps remain available for new Calluna plants). There are distinct advantages in encouraging a more diverse moorland plant community. Although the De-
Vegetation change following reduction in grazing schampsia is highly favoured by stock in the growing season, Calluna and V. myrtillus both provide valuable forage in autumn and winter when other species are less palatable and digestible. In addition, and of some consequence in the context of the study area, a mixed ericaceous community is more visually attractive, which befits its National Park setting. It also provides a better wildlife habitat appropriate to the Kinder Estate's inclusion in a Site of Special Scientific Interest. ACKNOWLEDGEMENTS Our thanks to the National Trust for permission to monitor on the Kinder Estate and for providing the sheep gathering data. The study was commissioned by the Peak District Moorland Management Project. We are grateful to the Steering Group, the rest of the study team and the anonymous referees for their helpful comments. REFERENCES
Anderson, P. & Yalden, D.W. (1981). Increased sheep numbers and the loss of heather moorland in the Peak District, England. Biol. Conserv., 20, 195 213. Clapham, A.R., Tutin, T.G. & Moore, D.M. (1987). Flora of the British Isles. Cambridge University Press, Cambridge. Evans, R. (1977). Overgrazing and soil erosion on hill pas-
63
tures with particular reference to the Peak District. J. Brit. Grassl. Soc., 32, 65-76. Grime, J.P. (1979). Plant strategies and vegetation processes. Wiley, Chichester. Grime, J.P., Hodgson, J.G. & Hunt, R. (1988). Comparative plant ecology a functional approach to common British species. Unwin Hyman, London. Gimingham, C.H. (1972). Ecology ofheathlands. Chapman & Hall, London. Hewson, R. (1977). The effects on heather Calluna vulgaris of excluding sheep from moorland in North-East England. Naturalist, 102, 133 6. Jones, Li. I. (1967). Studies of hill land in Wales. Welsh Plant Breeding Station, Aberystwyth, Tech. Bull., No. 2. King, J. (1960). Observations on the seedling establishment and growth of Nardus stricta in burned Callunetum. J Ecol., 48, 667 77. Moss, C.E. (1913). The vegetation of the Peak District. Cambridge University Press, Cambridge. Phillips, J., Yalden, D.W. & Tallis, J. (1981). Peak District moorland erosion stud)' Phase I report. Peak Park Joint Planning Board, Bakewell, Derbyshire. Phillips, M.E. (1954). Biological flora of the British Isles: Eriophorum angustifolium Roth. J. Ecol., 42, 612-22. Ritchie, J.C. (1956). Biological flora of the British Isles: Vaccinium myrtillus L. J. Ecol., 44, 291--99. Tallis, J.H. & Yalden, D.W. (1983). Peak District moorland restoration project Phase 2 report. Re-vegetation trials. Peak Park Joint Planning Board, Bakewell, Derbyshire. Webb, N. (1986). Heathlands. Collins, London. Wein, R.W. (1973). Biological flora of the British Isles: Eriphorum vaginatum L. J. Ecol., 61,601 15.