Recovery of four montane heath communities on Cairngorm, Scotland, from disturbance by trampling

RECOVERY OF FOUR MONTANE HEATH COMMUNITIES ON CAIRNGORM, SCOTLAND, FROM DISTURBANCE BY TRAMPLING

NElL G. BAYFIELD

Institute of Terrestrial Ecology, Brathens Research Station, Banchory, Kincardineshire, Scotland

ABSTRACT

Four montane heath communities on Cairngorm, Scotland, were subjected to human trampling and the initial damage anti subsequent recovery recorded over a period of eight years. Damage increased with the level of trampling but some species showed delayed damage; substantial die-back occurring during the following winter, or even later. A few species such as Trichophorum cespitosum rapidly replaced lost cover, but most species recovered very slowly. Observation over a substantial period seems necessary to assess the responses of slow growing mountain vegetation to disturbance by trampling.

INTRODUCTION

With the growth of leisure and outdoor pursuits in the last 15 years has come an increasing interest by ecologists in the effects of trampling on vegetation. This interest has often been stimulated by the deterioration of footpaths, and damage to plant cover at recreation sites such as nature trails (Burden & Randerson, 1972), chalk grassland (Streeter, 1971) and sand dunes (Liddle & Greig-Smith, 1975; Blom, 1976). The present study arose as a result of concern over the damage to vegetation and soils near ski lifts on Cairngorm, a mountain of 1245 m in the central highlands of Scotland (Watson et al., 1970). Although most damage on the hill appeared to be attributable to construction activity (Bayfield, 1971) some was also due to skiing and walking. As there was little information on the effects of trampling on montane vegetation, or its subsequent recovery, a series of plots were laid out on four communities, and subjected to controlled levels of trampling. In studies of this type one of the difficulties is knowing what levels and forms of 165 Biol. Conserv. (15) (1979)--© Applied Science Publishers Ltd, England, 1979 Printed in Great Britain

166

NElL G. BAYFIELD

trampling to use, and when and how often the treatments should be applied. Some workers have used mechanical feet or tamps to apply trampling (Wagar, 1964; Kellomaki, 1973; Kellomaki & Saastamoinen, 1975). These have the advantage of providing a precisely known force but the disadvantage of being ditticult to use on uneven ground, or on plots much larger than 1 m 2. Recently, portable motorised trampling machines have been devised that appear to overcome these objections (Canaway, 1975) but none was available at the time this study was initiated, and the trampling was applied by two men wearing climbing boots. Some investigators have tried to examine the effects of a range of frequencies of trampling (e.g. Goldsmith, 1974). This approach has the advantage of spreading the pressure over a period of time, the situation in practice at most recreation sites. A drawback is that to examine even a limited range of intensities requires a fairly large number of plots, and this makes examination of responses of more than a single community very time-consuming. An alternative approach adopted here, is to apply trampling over a short period of time with no further disturbance, and to examine responses in terms of the initial damage, and subsequent recovery. This method does not permit ready extrapolation to field situations where trampling is prolonged, but it allows comparison of the damage to species and communities by specific amounts of crushing, and lets recovery take place without setbacks from continuing disturbance. Nomenclature of vascular plants and bryophytes follows Clapham et al. (1962) and Warburg (1963). METHODS

Sites were selected on four plant communities on the north-facing side of Cairngorm; (1) wet lichen-rich Calluna-Trichophorum heath; (2) wet CallunaTrichophorum heath; (3) Calluna-Arctostaphylos heath and (4) Rhacomitrium heath. Mean cover values for principal species at each site are given in Table 1. At each site, plots 1.2 × 4-6m were walked over, a total of 0, 40, 80, 120 or 240 times. The trampling was provided by two 70 kg men wearing climbing boots. The 40- and 80-walk treatments were undertaken on a single occasion in July 1968, and the 120 and 240 treatments by three equal instalments of 40 and 80 respectively in July, August and September 1968. The plots were randomised within blocks, with three replicates of each treatment. At sites 2 and 4, a duplicate set of plots was trampled during winter (February-April) 1969. In practice staggering the 120- and 240-walk treatments over three months did not appear to have any consistent beneficial or detrimental effect by comparison with the unstaggered 40 and 80 treatments, so in the following account all four treatments were considered as a simple incremental series. For analysis purposes, each plot was split into five equal sub-plots. Visual estimates of cover and damage were made before trampling, and in September 1968

167

RECOVERY OF MONTANE HEATH COMMUNITIES

TABLE 1 MEAN VEGETATION COMPOSITION (UNTRANSFORMED ~ COVER _ S O ) AND OTHER FEATURES OF THE FOUR SITES ON CAIRNGORM USED FOR TRAMPLING EXPERIMENTS

Site number Type

1 Lichen-rich

2

3

4

CallunaTrichophorum

CallunaArctostaphylos

Rhacomitrium

heath

heath

620 N 7 deep blanket peat 32.2 + 7-5

640 W 10 shallow blanket peat 19.9 + 7.3

750 W 15 mountain podsol 57.0 + 9-2

11.5 + 2.5

10-3 + 2.2

CallunaTrichophorum

heath

heath Altitude (m) Aspect Slope (°) Soil type

Calluna vulgaris Erica tetralix~ Erica cinerea ~ Empetrum nigrum agg. Arctostaphylos uva-ursi Vaccinium myrtillus Vaccinium uliginosum Eriophorum vaginatum Eriophorum angustifolium Trichophorum cespitosum Narthecium ossifragum Juncus tr!fidus Carex bigelowii Molinia caerulea Deschampsia flexuosa Rhacomitrium lanuginosum Sphagnum rubellum

1050 N 7 mountain podsol

21.7 _+ 3-5 7.3 _+ 3-3 19.7 _+ 2"2 18.3 _+ 2.9 11"3 _+ 5"6 3-0 + 1-9 21-4 + 6"5 2-7 + 2-3

32.7 + 9.1 6.6 + 4.2

6.4 + 1.9 8-4 + 3.3 11-8_+4.3

7.0 + 2.3 11.6 + 7.2 14.5 + 5.3 48.3 + 14.1

Other mosses Lichens

10.5 _+ 2-8

2.5 -t- 0.9

12.1 + 4.8 47-3 4- 12.8

5.3 _+ 1.3

5-6 + 1.8 16.4 + 6.6

8.3 + 2.4 5-7 _+ 0.7

and 1969, August 1970 and August 1976. Visual estimates were made by two people working together. In the 1968 and 1969 analyses only, actual damage was estimated. The cover of intact or surviving vegetation was recorded at all five analyses, and these data were adjusted to minimise the effects of any observer bias between analyses by expressing them as a percentage of values for the untrampled plots. In addition, since the amounts of constituent species varied slightly between plots, a correction factor was applied based on the proportions present before trampling: Relative cover =

where

cf

cover on trampled plots x cf x 100 ~o cover on control plots initial cover on control plots "~ / i~ c~ on t ~ d plototsJ RESULTS

Initial damage The superficial appearance of plots three months after trampling varied from site

168

NEIL G. BAYFIELD

to site. On the Empetrum-Rhacomitrium heath (site 4)there was a lot o f loose moss left on the surface that made some o f the plots look severely damaged. Sphagnum rubellum fragments on the wet lichen-rich Calluna-Trichophorum heath (site 1) created a similar effect. The other two sites, although clearly somewhat worn by the trampling treatments, did not give the impression o f such serious disturbance. Bare g r o u n d was exposed at three of the sites. The exposed surface was peat at sites 1 and 2, but both peat and mineral soil at site 3. The extent o f bare g r o u n d at site 1 appeared greatest at the analysis after 1 year, when most o f the debris o f lichens and heather had blown away. On the Empetrum-Rhacomitrium heath (site 4) there was no completely bare ground, but patches o f dark brown apparently dead Rhacomitrium lanuginosum stems were exposed where the surface moss had been worn away. At all four sites the a m o u n t o f unvegetated ground, and o f d a m a g e to individual species, increased with the a m o u n t o f trampling (Table 2). F o r some TABLE 2 ASSESSMENT OF DAMAGE DUE TO TRAMPLING AT THE FOUR SITES AFTER THREE MONTHS. DATA ARE ~o COVER (UNTRANSEORMED) EXCEPT WHERE INDICATED. ANALYSIS OF VARIANCE: *, p < 0-05; **, p < 0.01, OTHER VALUES NOT SIGNIFICANT. DIFFERENCES BETWEEN BLOCKS WERE NOT SIGNIFICANT IN ANY OF THE COMPARISONS

Level of trampling Lichen-rich Calluna-Trichophorum heath (Site 1) 0 Bare peat Crushed Trichophorum Broken or bruised Calluna Crushed Sphagnum (as % of Sphagnum present) Calluna-Trichophorum heath (Site 2) Bare peat Crushed Trichophorum Dead or loose Rhacomitrium Calluna-Arctostaphylos heath (Site 3) Bare ground Crushed Trichophorum Broken Calluna Rhacomitrium heath (Site 4) Crushed Empetrum and Vaccinium Dead Rhacomitrium Weight of litter (g)

1.3 1-5 5-4 0

40 10.7 10.5 5-3 22.0

80 18.0 16.4 7.9 85.3

120 7.6 23.4 9.3 78.3

240 f ratio 20.3 2.3 34.3 24.9** 10-6 7.2* 67-0 10.6"

1-6 0.9 2-8

2.3 3.8 5-0

3.1 9.0 3.8

4.3 13.5 5.8

8-1 30.6 13.4

6.2* 42.7** 11.1"

3-1 0-3 0"9

5.0 2.2 2-0

9.4 4-6 2-9

12.8 4.6 1.9

22-9 5.5 3.9

11.7" 9.5* 3.6

2.3 2.4 12

5.3 7.0 113

3.9 7.4 156

5.7 10.5 355

9.9 18-3 851

16.6"* 6.9* 11.8"

species, such as Trichophorum cespitosum and Sphagnum rubellum, damage was easily distinguished. In other cases it was either variable or difficult to pick out. Calluna vulgaris, for example, only showed small increases in d a m a g e after three m o n t h s and these were not always statistically significant. A n important factor with this and other ericaceous species, however, was the p h e n o m e n o n o f delayed damage. This is illustrated by the data for relative intact cover (Figs. 1 4 ) .

169

RECOVERY OF MONTANE HEATH COMMUNITIES

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agnum rubellum

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NUMBEROF WALKS Fig. 1.

Relative intact cover of species in the lichen-rich Calluna-Trichophorum heath on Cairngorm (site 1) at various times after disturbance by trampling.

170

NElL G. BAYFIELD

100 8060.

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NUMBEROF WALKS Fig. 2.

Relative intact cover of species in the Calluna-Trichophorum heath on Cairngorm (site 2) at various times after disturbance by trampling.

Delayed damage Calluna vulgaris, Vaccinium spp. ( V. myrtillus and V. uliginosum) and Empetrum nigrum agg. showed comparatively little damage at the analysis three months after trampling, but suffered substantial dieback during the subsequent winter, so that their intact cover was minimal at the analysis after a year. Erica spp. (E. tetralix and traces of E. cinerea) and A rctostaphylos uva-ursi appeared to have reacted similarly, although they were not formally recorded at the three-month analysis. Eriophorum spp. (E. vaginatum and E. angustifolium) had minimal cover two years after disturbance. Delayed damage appeared to result from a gradual dieback of bruised tissues, particularly as a result of frost damage. Watson et al. (1966) found that heather bruised, for example by vehicle wheels, was particularly susceptible to frost damage. This may be because crushed shoots of this species develop high water potential deficits that can persist for several months, making water uptake difficult at times of stress (P. Smith, pers. comm.).

RECOVERYOF MONTANEHEATHCOMMUNITIES .

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NUMBER

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OF WALKS

Fig. 3. Relativeintact coverof speciesand the occurrenceof seedlingsin the Calluna-Arctostaphylos heath on Cairngorm(site3) at varioustimesafter disturbanceby trampling. Carex bigelowii, one of the components of the Rhacomitrium heath, actually had higher cover a year after trampling than before. New growth appeared to occur from sub-surface stems, possibly as shoots that would otherwise have appeared the following spring. The increase was only temporary, possibly because of dieback of some of the new growth during the following winter. Since this species was only a minor component of site 4 the increase in cover made little difference to the overall appearance of the plots.

172

NEIL G. BAYFIELD

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NUMBER OF WALKS

Fig.4. Relativeintactcoverof speciesin the Rhacomitriumheath on Cairngorm(site4) at varioustimes after disturbance by trampling. Trampling crushed and broke lichen thalli. The extent of the damage could not be readily assessed at the first analysis after treatment, because of the difficulty of distinguishing intact and broken fragments of lichens. After a year the loose fragments had blown away, and the surviving cover of lichens was then seen to follow the usual pattern of decline with increasing amounts of trampling (Figs. 1 and 3). There were two possible sources of error in recording lichen responses; (1) several species were involved, probably with differing responses to trampling; and (2) their appearance varied with moisture content. Some species not only shrivel when they dry up but may also change colour. For example, dry Cetraria islandica is much darker, and only about a third of its moist size. Other species such as Cladonia impexa contract much less on drying, and there is little colour change. These difficulties probably contributed to the rather variable response data for lichens, particularly as weather conditions varied from analysis to analysis.

173

RECOVERY OF MONTANE HEATH COMMUNITIES

Recovery After eight years, sites 4 and 1 looked completely recovered and close inspection was necessary to detect any differences between treatments. At site 2, some plots still looked slightly worn, and on site 3, the 240-walk plots stood out as substantially more disturbed than the remainder. These subjective impressions were confirmed by data for changes in species cover; data for untrampled and 240-walk plots are summarised in Table 3. In most cases there were changes in the proportions of species on the undisturbed as well as the trampled plots, but most net changes were similar on trampled and untrampled ground. The main exceptions were Calluna vulgaris (sites 1,2, 3) which had substantially less cover on trampled plots even after eight years, Sphagnum rubellum (site 1) with much less cover on the 240-walk plots, and bare ground which was still largely exposed at site 3. TABLE 3 COMPARISON OF MEAN CHANGES IN COVER OF PRINCIPAL SPECIES ON CONTROL AND 240-TRAMPLE PLOTS AT THE FOUR SITES, AFTER EIGHT YEARS (~o). ANALYSIS OF VARIANCE: *, p < 0"05; **, p < 0.01; OTHER DIFFERENCES NOT SIGNIFICANT

E

E =

"~.

=

E

~

o

Lichen-rich CaUuna-Trichophorum heath (Site 1)

Initial cover (overall mean) Untrampled plots 240 tramples Calluna-Trichophorum

32

21

11

14

-3 +8 -2 -14"*+3 +5

-4 -1

48

12

0

+2 -2 -5 -8**

0 +1

5 +5 +2

0 0 +2

heath (Site 2) 20 Initial cover +15 Untrampled +2* 240 tramples Calluna-Arctostaphylos

33 10 10 +3 +2+11 +1 + 4 + 7

7 -I +1

heath (Site 3) 57 Initial cover +14 Untrampled -10" 240 tramples Rhacomitrium heath (Site 4) Initial cover Untrampled 240 tramples

6 +5 +5

16 +12 +16 47 +9 +13

6 -2 -4

7 -3 -6

4 -3 +11"* 22 38 8 12 12 0 -7 -20 0 - 8 - 9 +1 -11 -20 -4 -7 -4 +2

174

NElL G. BAYFIELD

Possibly because of the persistence of bare ground, site 3 was the only one at which seedlings were recorded (Fig. 3). The numbers noted increased with the level of initial disturbance. Nearly all seedlings were Trichophorum cespitosum, hut there were a few Carex sp. and some Calluna vulgaris. Although occasional seedlings may have been present at other sites they were not sufficiently conspicuous to have been recorded. A more detailed picture of the recovery of individual species at the four sites was obtained from the relative cover data for successive analyses (Figs. 14). The species at the four sites could be grouped into those that recovered fairly rapidly from the effects of disturbance, and those in which recovery was more prolonged. Species in the first group were Trichophorum cespitosum (sites 1-3), Vaccinium spp. (site 4) and Empetrum nigrum agg. (site 4). Each had replaced more than half the loss of plant cover within two seasons growth. Recovery was most complete in the case of the Trichophorum, a deciduous species with growth apices buried below the surface of a compact tussock of old shoot bases. This growth form seemed to provide considerable protection from the crushing effect of trampling. After two years nearly all the cover loss due to crushing had been replaced. The Vaccinium species were also deciduous and their recovery may have been aided by the ability to produce a complete replacement set of leaves in the spring, instead of only partial replacement as in the case of most Ericaceae. The rapid recovery of the evergreen species Empetrum nigrum agg. was not so readily explained. Perhaps the extensive subsurface shoot system contained plentiful food reserves for replacement growth. The other Ericaceae examined (Calluna vulgaris, Erica spp., and Arctostaphylos uva-ursi) recovered more slowly. They were all growing at sites lacking the thick Rhacomitrium carpet of site 4, that probably absorbed much of the impact of trampling. Recovery of the Calluna was poor at all three sites at which it was present. Replacement growth was partly basal, and partly by production of new shoots along old stems, the new growth being sparse and not very vigorous. Calluna is known to regenerate quite readily after fire and clipping. Miller & Miles (1970) found that regeneration was most satisfactory from heather 6-10 years old, and declined progressively with age. They attributed this decline mainly to a decrease in the number of plants/m 2 from which regeneration could occur. A further contributory factor suggested by Mohamed & Gimingham (1970) is a progressive reduction with age in the number of active or potentially active meristems. Most of the heather on Cairngorm was probably elderly since there was no history of burning or grazing, and poor regeneration was consequently not surprising. Recovery of Erica spp. was also slow, but more complete than Calluna, with relatively higher cover after eight years on heavily trampled plots than on the untrampled controls. The final cover of Eriophorum spp., too, was slightly more on trampled than untrampled plots, except in the case of the lightest treatment. By contrast, recovery of the most severely damaged Sphagnum rubellum was almost

RECOVERY OF MONTANE HEATH COMMUNITIES

175

negligible, although the 40- and 80-walk plots eventually showed good regrowth. Recovery of Rhacomitrium lanuginosum was uneven, with increases in cover apparently followed by decreases, both at site 4, where it was a major component, and site 2 where it had lower initial cover. This irregular pattern may have resulted partly from the variable appearance of this species, since it is considerably more conspicuous when wet, and partly from it being a ground layer species, to some extent obscured by vascular species. Lichens also showed erratic patterns of recovery growth, but the overall trend with both lichens and the Rhaeomitrium was for complete recovery by the final analysis.

Integration of damage and recovery data It is difficult to compare the responses of species or communities when some show delayed damage, and recovery varies between rapid and very slow. One method of integrating damage and recovery data is given in Fig. 5, which shows relative cover for principal species after one year, to represent initial damage, plotted against that after eight years, to show subsequent recovery. In each case data are for the most severely trampled plots. This presentation reveals three groups of species with respect to trampling susceptibility: (1) those most susceptible--with high initial damage and poor recovery ( Calluna vulgaris, Empetrum nigrum agg., Sphagnum rubellum and Aretostaphylos uva-ursi; (2) those with moderate susceptibility-moderate to high initial damage, fairly good recovery (Rhacomitrium lanuginosum, Trichophorum cespitosum, Vaccinium spp. and lichens); and (3) those with low susceptibility--low or moderate damage followed by an increase in relative cover (Erica spp., Eriophorum spp. and Carex bigelowii). There were a number of ways of ranking the four sites. Several species (Calluna vulgaris, Trichophorum cespitosum, lichens and Erica spp.) were found at sites 1,2 and 3, and in each case initial damage was least at site 2 and greatest at site 1 (1 > 3 > 2). Only the Rhacomitrium was common to sites 4 and 2, damage being less at site 4. However, a ranking based on the total intact plant cover after trampling indicated damage at site 1 > 3 > 4 > 2. Alternatively, if the sites were listed in order of the amounts of recovery growth, then site 1 > 3 > 2 > 4 on the basis of individual species responses, or 1 > 4 > 3 > 2 based on overall cover. With any of these rankings, the most damaged site (site 1) also showed the greatest recovery.

Summer and winter trampling There was very little difference in responses to trampling during winter or summer, at either sites 2 or 4. The main exception was the production of a great deal of peaty mud by the winter trampling at site 2, which made the plots look very severely damaged. By the analysis in August 1969, however, all traces of mud had gone, and damage to the vegetation was very similar to that caused by trampling in summer. There was no comparable production of mud at site 4, which was better drained, and on a less peaty soil. An analysis of variance showed no significant effect

176

NElL G. BAYFIELD

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RECOVERY OF MONTANE HEATH COMMUNITIES

177

of season on species responses. Although there may in fact have been some slight effect of season (for example, there was on average slightly more bare ground on plots trampled during the winter) it could not be satisfactorily distinguished because of the comparatively high variability between replicates. Greater replication, or a more sensitive analysis procedure, might have overcome this difficulty.

DISCUSSION

The damage and recovery at sites 1 and 2 were largely as expected, but the resilience of site 4 was greater than had been anticipated. Rhacomitrium heath gives the impression of great fragility because of the ease with which the moss breaks up. Presumably the thick carpet of moss not only helped cushion the impact of feet (Holmes & Dobson, 1976), but provided a suitable substrate for replacement Rhacomitrium growth. If damage had proceeded to the point where mineral soil was exposed, recovery would presumably have been very much slower. This was certainly the case on the Calluna-Arctostaphylos heath at site 3, which had the poorest overall recovery. Although there were a number of seedlings colonising the bare ground at this site, the cover achieved by seedling growth reduced the cover of bare ground very little. This poor growth seemed subjectively to be due to the dryness of the site. In spite of the steep slope there was no clear evidence of soil erosion, just very slow colonisation by vegetation. The comparison of damage sustained by trampling at different times of year was not very satisfactory. Although there appeared to be no pronounced effects of season, further work might well distinguish slight differences in the effects of winter and summer use. Liddle (1975a) has found greater damage in winter than in summer on sand dune pasture, and Bayfield & Lloyd (1973) concluded that damage due to trampling was relatively greater in winter than in summer on the Pennine Way long distance footpath. Holmes & Dobson (1976) found that mountain vegetation near 2900 m in Yosemite National Park was usually more vulnerable to trampling in late summer than in spring or early summer, and this comparison is one that might have usefully been applied in the present study, since the main growing season on Cairngorm is in the mid-May to early-July period, and in this sense both 'summer' and 'winter' trampling treatments were applied when the vegetation was dormant or very slow-growing. This study illustrates some of the difficulties of comparing the responses of plant communities to trampling. There is the problem of deciding when to assess damage. Several species in the four communities showed delayed damage, with minimal intact cover at the analysis after a year or even later, rather than after three months. At site 1 this was also true of bare ground, which was partly obscured at the first analysis by plant litter that later blew away. Delayed responses to trampling have apparently not been noted in other habitats. It is possible that few types of

178

NEIL G. BAYFIELD

vegetation respond in this way, but equally there have been few studies that would permit detection of delayed responses. Some workers have mainly been concerned with situations where disturbance was continuing (Goldsmith et al., 1970; Chappell et al., 1971). In other cases damage or recovery were only recorded on one occasion (Kellomaki & Saastamoinen, 1975; Holmes & Dobson, 1976). While short-term studies may be adequate for many lowland situations, a longer period of observation seems desirable for slow-growing mountain vegetation. Another problem is that of assessing the ability of plants to recover from damage. Liddle (1975b) has suggested that there may be a relationship between primary productivity and the tolerance of vegetation to trampling. However, although a capacity for primary productivity might well influence the ability of a plant to recover, Liddle's hypothesis was not based on recovery, but on responses over no more than 20 weeks on the number of tramples necessary to cause a 50 ~o reduction in cover or biomass. It is clear that assessment of the responses of plants to trampling should take account both of damage sustained, and ability to replace damaged tissues. The present study shows that assessment of recovery can be difficult due to delayed damage, and the varying patterns of recovery growth in different species. Some such as Trichophorum cespitosum can apparently make significant recovery growth in the first season after disturbance, and continue to improve in subsequent years. Others, such as l/accinium spp., may show good recovery the first season, but little thereafter. Lichens, Sphagnum rubellum and Calluna vulgaris appear to recover gradually over a lengthy period. The presentation of data on both initial damage and subsequent recovery (Fig. 5) goes some way towards integrating the two parameters but has the disadvantage that the selection of one and eight years as times for assessment is an arbitrary choice. It might not be appropriate for comparisons with other communities on Cairngorm or elsewhere, and slightly different patterns of damage and recovery would be shown if the assessment times were three months and one year, or one and two years. Nevertheless, this approach shows that the same species in different communities may respond in broadly similar ways. Unfortunately there are insufficient data to permit an analysis of how species responses are modified by features of the site such as slope, moisture content and soil type. This information might be sought using only one or two trampling treatments, on a wide range of sites. Such an investigation could have real practical value for site management, but would need to be backed up by further detailed studies, of the effects of trampling at different seasons, and of the effects of prolonging trampling as well as applying it over short periods. On the evidence of the present work it would be necessary to extend observations over a substantial number of years to assess adequately responses to disturbance. ACKNOWLEDGEMENTS

I should like to thank Mr S. Moyes for his assistance with this work, Mr D. Brown for statistical advice, and Dr S. W. Greene for comments on the manuscript.

RECOVERY OF MONTANE HEATH COMMUNITIES

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