The effects of human trampling on the fauna of grassland litter

THE

EFFECTS

OF HUMAN TRAMPLING ON THE OF GRASSLAND LITTER

FAUNA

ERIC DUFFEY Institute o f Terrestrial Ecology, Monks Wood Experimental Station, Abbots Ripton, Huntingdon, Great Britain

A BSTRA C T

The effects of trampling on the invertebrate fauna of grassland litter was studied using two levels of treading intensity over a period of 12 months. Changes in the structure of the litter after treatment (fall in total volume, proportion of air space) were measured with a Quantimet Image Analysing Computer. The total volume fell by 81% and the proportion of air space fell from 63% to 38% in the litter samples receiving 10 treads~month. The overall effect of treading on the fauna was a substantial decline in numbers and species, although this did not apply to all groups. At the species level there was considerable variation in sensitivity to treading. The differences in the fauna between the two levels of treading were small and non-significant with the exception of the spiders. The invertebrate fauna of grassland litter appears to be affected by levels of trampling much lower than those required to produce changes in the structure and species.frequency of living plants.

INTRODUCTION

The ecological effects of human trampling on areas of wildlife interest are now recognised as important modifying influences likely to increase in the future as the public makes greater use of nature reserves, National Parks, and other types of unspoilt countryside. Speight (1973) has recently reviewed the considerable literature dealing with research on recreation ecology and, although there have been numerous recent studies on floristic changes brought about by trampling (e.g. Perring, 1967; Bayfield, 1971, 1973; Chappell et al., 1971; Burden & Randerson, 1972; Streeter, 1971; Liddle, 1975), the effects of this type of disturbance on groundliving invertebrates have been largely neglected. Chappell et al. (1971) examined small soil cores 4 cm X 5 cm taken from three areas of chalk grassland: (1) long grass and minimum wear; (2) moderately trampled grassland 5 cm in height; and 255 Biol. Conserv. (7) (1975)--O Applied Science Publishers Ltd, England, 1975 Printed in Great Britain

256

ERIC D U F F E Y

(3) ground with heavy wear. Their results showed that there was a sharp fall in numbers of individuals in some invertebrate groups with increasing trampling intensity although there are no data available on the number of people (or treads) causing the observed effects. However, in the case of plants more information is available. Burden & Randerson (1972) described the vegetation changes which took place after 7,729 people had walked along a nature trail through beech woodland and chalk downland during a period of 8 days, averaging 966/day. Burden (1970) showed that about 7,900 'walks' in 8 days over woodland leaf litter caused a reduction in the mean depth of litter from 6.9 cm to 4"28 cm over a 20 X 30 m area. Bayfield (1973) recorded the increase in width of paths in relation to intensity of use on a Scottish mountainside using thin wire trampleometers (sections of wire, positioned vertically in turf on a pathway and flattened by treading. Proportion of total which are flattened indicates intensity of use). Mrs A. Coker (pers. comm.) found that 10 treads/week over a 12-month period caused little or no change in the vegetation of a chalk grassland, but when the trampling was increased to 90 treads/week, significant changes were recorded in the plant species and frequency. The examples cited deal mostly with situations where heavy use caused physical damage to the plant life and created bare patches of soil. However, long before such effects on plants become apparent, changes appear to take place in the invertebrate fauna associated with the vegetation or with the leaf litter. Severe treading, whether by the human foot or by domestic stock combined with grazing, usually causes a rapid loss of leaf litter by dispersal and fragmentation, together with a decrease in the height of the living vegetation. These changes in the microhabitat probably influence the ground fauna more significantly than destruction of individual animals by the impact of treading. There is also evidence that simple disturbance effects without damage to vegetation may influence the population of some insects. Jones (1968) found that the movement of large carabid beetles in a young oat crop disturbed the ovipositing frit fly (Oscinellafrit L.) so that fewer eggs were laid. She also found that the same effect could be produced by artificial disturbance caused by a bead on a wire arm travelling through the vegetation. It is possible that the movement of grazing animals or human visitors in a grassland may influence a variety of insects in the same way. The following account is of an experiment which attempted to measure the effects of trampling by man on the invertebrate fauna of leaf litter in a 7-year-old grass ley adjacent to the Monks Wood Experimental Station, Huntingdon, Great Britain, during a period of 12 months (March 1970March 1971).

E X P E R I M E N T A L SITE A N D M E T H O D S

The site measured 60 m X 50 m and was situated on heavy, calcareous boulder clay. Within this area 50 X 40 m was divided into 20 squares of 10 m × l0 m and

T R A M P L I N G AND GRASSLAND FAUNA

257

the remaining sector, 20 m × 50 m, was reserved for samples of grass leaf litter which were later sectioned for an assessment of structural changes. Prior to 1963 the site had been under continuous arable cultivation and was sown to grass in May 1963 using 5 lbs (2-27 kg) each of meadow fescue (Festuca pratensis Huds.), timothy (Poa pratense L.) and rye grass (Lolium perenne L.), together with 2 lbs (1.6 kg) of wild white clover (Trifolium repens L.)/acre (0-4 ha). Thereafter until 1970, the site was mown each year for a hay crop, with the result that after 7 years comparatively little leaf litter had accumulated over the ground surface. For example, litter collected from three 1 m 2 quadrats and five 0-75 m 2 quadrats in March 1971 gave a mean value of 23'0 g dry weight/0.04 m% the area covered by each litter bag (575 g/m2). Because there was insufficient material to provide adequate samples for counts of the fauna in relation to treading intensities, it was decided to use grass taken from the previous year's hay crop. The use of this 'artificial' litter made it possible to construct a standard sample consisting of 125 g of oven-dried litter enclosed in a nylon mesh bag measuring 20 X 20 × 8 cm. The litter was sterilised at 80°C for 48 h before use. The 1 cm mesh size of the nylon bag allowed invertebrate animals to colonise from the surrounding vegetation but prevented entry by mice and voles seeking a nest site. Each bag was held in place by two metal tent pegs, attached at opposite corners. A total of 141 sample bags was made up and distributed at random within the twenty 10 X 10 m squares as follows: 22 bags used as controls; 25 bags 'lightly' trampled (5 treads/month); 25 bags 'heavily' trampled (10 treads/month); 60 bags used to monitor changes in the litter fauna at 3-month intervals throughout the experimental period; 9 bags (3 controls, 3 'lightly' trampled, 3 'heavily' trampled) used to obtain sections of the treated and untreated litter at the end of the experiment. The treading experiment was carried out by a 82.7 kg (182 lbs) man wearing rubber boots. Each litter bag receiving 'light' treading was trodden once on each of 5 consecutive days in the first week of each month during the 12-month period (60 treads per annum). Similarly the bags receiving 'heavy' treading were trodden twice on each of the same 5 consecutive days (120 treads per annum). During March and April 1970 and the winter months of 1970-71, wet patches formed in parts of the experimental area, occasionally with standing water which remained for a few days. At times, therefore, some litter bags were much wetter than others and the treading forced mud into them. The 60 litter bags used to monitor changes during the ! 2-month period were taken up, 20 at a time, at 3-, 6- and 9-month intervals to obtain a record of the fauna. The 22 control bags completed this record at the end of the 12-month experimental period. The fauna was obtained from the litter bags

258

ERIC DUFFEY

(monitoring, treated and controls), by use of a Tullgren funnel heat extraction apparatus.

CHANGE

IN STRUCTURE

OF THE L I T T E R A F T E R T R E A D I N G

During the 12-month experimental period the artificial litter in the grass ley began to decompose and break down so that, even in the absence of trampling, changes in the structure took place. The comparative breakdown rates of natural litter and the hay used in this experiment are not known and may differ because of variation in the chemical composition of the two types of litter (Table 1). Analysis of material TABLE

I

COMPARATIVE ANALYTICAL DATA FOR 5 SAMPLES EACH OF HAY LITTER AND NATURAL GRASS LITTER (ANALYSES BY CHEMICAL SECTION, MERLEWOOD RESEARCH STATION)

Hay litter samples Natural grasslitter samples

1 2 3 4 5 6 7 8 9 10

%

%

% K

% Ca

% P

% N

% Si

Crude lignin

Soluble carbohydrate

2.1 2.0 2.1 2.1 2.2 0.21 0.27 0.25 0.23 0.16

0.32 0.30 0.31 0.31 0.33 0.28 0.29 0.30 0.31 0.31

0.18 0. i7 0.18 0.18 0.18 0.17 0.17 0.17 0.18 0.18

0.78 0.76 0.81 0.76 0.81 1.3 1.3 1.3 1.4 1.4

0.85 0.97 0.82 0.86 0.76 2.9 2.8 3.3 3.1 3.0

18.8 16.3 30.2 27.3 8.7 30.2 28.0 10.5 28.0 11.4

13.6 14.1 14.3 14.0 14.2 6.7 6.5 6.4 6.7 6.8

% C

46.5 44.2 43.6 44.9 43.8 42.9 40.6 42.4 42.4 41.3

before the experiment showed that, proportionally, there was eight times as much potassium and over twice as much soluble carbohydrate in the hay than in the natural grass litter, while the latter had twice as much nitrogen and three times as much silica. Before the experiment the mean depth of the litter bags around the mid-point was found to be 8.90 cm ( ± 0.11). After 6 months the mean depth (21 samples) had fallen to 6.40 cm ( +_2.40), after 9 months (17 samples) to 5.50 cm ( _+0.18) and after 12 months (20 samples) to 4.20 cm ( _+0.18). On the other hand, the values for the litter bags subjected to 12 months' treading were as follows: 5 treads/month (10 samples) 2.40 cm ( -+0.12) and 10 treads/month (20 samples) 1.70 cm ( _+0.18) (Fig. l(a), (b), (c) and (d)). Three control bags which were oven-dried at the end of the experimental period showed a mean weight loss of 34.16% (125 g to 82.30 g) while a single 10 treads/month sample, from which the soil had been carefully washed out, showed a dry weight loss of 93.84% (125 g to 7.70 g). No other entire litter bag subjected to treading was examined in this way because of the extreme difficulty of removing all the soil particles without loss of litter fragments during the washing

259

TRAMPLING AND GRASSLAND FAUNA

process. The soil content in this instance was 5.44 g, 41.30% of the total sample weight. Figure 1(a) shows that fresh litter is a loose, open structure full of small air spaces where invertebrate animals can move freely to find shelter and food and, in the case of spiders, construct snares. As decay progresses the leaves and stems weaken and gradually break up--although this was relatively slow in the controls compared with the trodden litter, which was fragmented by the physical impact of the human foot. As the structure and microclimate of ground vegetation is of considerable importance to the fauna, a quantitative measure of the change in structure between the control and trodden litter bags was made using the sectioning technique of

d o I

.

.

.

.

.

. . Cms

.

.

1o I

Fig. I, Photographs of sections of trampled and untrampled litter after embedding in gelatin: (a) at the beginning of the experiment; (b) control (untrampled) litter after 12 months in the field; (c) after 60 treads during a 12-month period; (d) after 120 treads during a 12-month period.

260

ERIC DUFFEY

Anderson & Healey (1970) (small soil cores embedded in gelatin, hardened and then sectioned). Each of the litter bags set aside for this purpose was frozen in situ using CO2 ice within a wooden frame. When frozen, the bag was carefully removed from its site and taken to the laboratory in an insulated container. The sample bags were larger than Anderson & Healey's soil cores (10 × l0 X 6 cm) and some difficulties were encountered in solving the technical problems of embedding them in gelatin. After thawing the samples were placed in a large glass desiccator (Fig. 2) in which a partial vacuum was created using an electric pump. The desiccator was held in a warm water bath at 37°C so that the gelatin solution, which entered the container beneath the litter, was able to flow freely and penetrate into the air spaces. Rate of penetration varied from sample to sample in relation to compactness and the amount of soil forced into the litter by treading. Three changes of 20% solution (wt/vol) of gelatin were necessary in order to remove excess water and enable the solution to set firmly when cooled. After removal from the gelatin block each sample was carefully cut into two equal parts and immersed in 10% formalin for 4-7 days to harden. The nylon mesh which still enclosed the sample was then removed and sections cut from the inner side of each half using a bacon slicer. Because of the importance of obtaining a complete section it was seldom possible to cut a slice thinner than about 2 mm. Sections less than this in thickness tended to fragment during the cutting process. Soil material separated from the litter and hard undecomposed grass stems tore the gelatin layer. A total of 135 sections from each of the sample bags were placed on a groundglass screen illuminated from below, and photographed. A selection of the blackand-white prints obtained were subjected to the scanning technique of the Quantimet Image Analysing Computer which enables one to measure with Vacuum gauge

Vaccum regulator tap

ter•

Gelatin inlet tube

T

Water hea Safety reservoir Vacuum pump

t II I ,I1

{,

~

~

Loop usedto hold litter j b a g belowgelatin surface

i~

~

Fig. 2. Apparatus for embeddinglitter bags in gelatin.

Litter bag Hot bathwater

261

TRAMPLING AND GRASSLAND FAUNA

accuracy the ratio of litter (black areas) to air space (white areas). The image was projected on to a television screen on which a grid of 500,000 points, each forming a small square of 0.0923 mm 2, had been superimposed. The technique is able to detect whether each point lies on a background of white or black or on an interface between the two. As the area of each litter section is known it is possible to calculate the proportions of black (occupied by stems and leaves) and of white (air space). If all the sections were similar in structure the number of points falling on the black/white interfaces (intercepts) would provide a measure of the total number of air spaces, an important feature of the litter habitat. The sizes of the air spaces can also be calculated. Unfortunately, these data for the artificial litter samples cannot be used for comparative purposes because of the artificial arrangement of the material in the nylon mesh bags. Unlike natural grass litter, which tends to fall in the direction of the prevailing wind, the hay litter, pushed into the nylon bags, generally formed a circular mass. This resulted in some sections falling in the same plane as the stems and leaves while others cut the material obliquely or transversely. TABLE 2 CHANGE IN VOLUME AND PROPORTION OF AIR SPACE IN LITTER BAGS AND SLICED SECTIONS BEFORE AND • AFTER TREADING

Pretreatment Volume cm 3 % fall f r o m pre-treatment % o f section consisting of air spaces

3560.0

Controls 5 treads~month (after 12 months) (after 12 months)

10 treads/month (after 12 months)

1600.0

i 128.0

708.0

--

55.1

68.4

81.0

--

63.0

54.0

38.0

However, comparisons between the proportions of total litter and air space in the sections are less subject to error. Table 2 shows that the proportion of air space in the controls (63%) fell 38% in the 10 treads/month samples. The mean depth measurements of the litter bags can be used to calculate the total volumes before and after treatment (Table 2). After 12 months the volume of the controls had fallen by just over 50%, due to natural decay, while the 10 treads/month samples fell by 81%. It is not known precisely what happens to the fauna during the quick freezing process in the field nor whether changes take place in the positions of the dead animals during thawing prior to embedding in gelatin. The spaces between the particles in soil sections are very small and not much movement seems likely, but in loose litter the air cavities are co nsiderably larger so that individual animals may be dislodged by movement or by the flow of gelatin. For example, 18 sections cut from a control sample gave a mean of 23.10 spaces with a diameter of >2.2 mm and 9.2 spaces with a diameter > 4.4 mm per section.

262

ERIC DUFFEY

A total of 18 sections (9 control, 5 'light' treading and 4 'heavy' treading) included entire and large parts of litter invertebrates. The first group showed parts of isopods, slugs, staphylinid beetles, the thorax and palps of an immature male Pardosa sp. (Lycosidae) spider, whole mites, both in air spaces and within the hollow grass stems, a weevil (Apion sp.) and numerous fruiting bodies of the fungus Chaetomium elatum (Kunze ex. Fries), a widespread species known to be strongly cellulolytic. Fewer animals were found in the trampled litter but another whole mite was found inside a hollow grass stem, while an entire beetle (Notiophilus sp.) and parts of spiders, isopods and staphylinid beetles were also discovered.

FAUNAL CHANGES IN THE MONITORING SERIES OF LITTER SAMPLES

The monitoring series of 60 litter bags was placed at random in the experimental area at the same time as the control and treated bags. They were taken up 20 at a time, every three months, so that a record of the development of the fauna could be made at 3-, 6- and 9-month intervals. At the end of the 12-month period the composition of the fauna from the control bags was recorded. When first put out in the grass ley during March 1970 the dry sterilised bags of litter probably presented a relatively unfavourable environment for grassland invertebrates. Nevertheless, the spring rainfall and the shading effect of the growing vegetation soon created moist conditions close to the ground and by June, three months later, several invertebrate groups had become established. Seasonal changes in the numbers and relative abundance of different species, depending on type of life history, are characteristic of invertebrate animals so that the composition of the fauna in the litter bags, at any time, was influenced by this phenomenon, together with the processes of colonisation of the litter habitat as the material began to decompose (Table 3). For example, Coleoptera larvae attained high numbers soon after the bags were placed in the field, but declined thereafter. Similarly, Heteroptera were most abundant in the first set of bags to be sampled, mainly due to the summer peak of Berytinus minor (H.-S.) which accounted for 74 out of the 76 specimens recorded in Table 4. Spiders also colonised the bags rapidly and reached highest numbers in September, when the population density of this group is normally at its peak in ground vegetation and litter. Other groups were slow to occupy the litter bags, for example Isopoda, Diplopoda, Mollusea and Annelida, but increased rapidly in numbers during the winter months. The Mollusca, Isopoda, Araneae, Hetetoptera and Coleoptera were determined to species level and the change in numbers recorded (Table 4). Of these groups Araneae and Coleoptera were most abundant in the first 3 months and the Mollusca and Diplopoda the least abundant. In all cases except that of the Heteroptera there was a steady increase in numbers of species, with totalsof 29 recorded in June 1970 and 99 in March 1971.

263

TRAMPLING AND GRASSLAND FAUNA

TABLE 3 ]'HE DEVELOPMENT OF THE FAUNA (MEAN NUMBER/LITTER BAG WITH STANDARD ERRORS) IN THE MONITORINGSERIESOF LITTERSAMPLESOVERA 12-MONTHPERIOD, MARCH 1970-MARCH 1971. ACARIAND COLLEMBOLA NOT COUNTED

Coleoptera Coleoptera larvae Heteroptera Homoptera Hymenoptera Diptera Diptera larvae Thysanoptera Lepidoptera larvae Araneae Opiliones Isopoda Diplopoda Chilopoda Mollusca Annelida Mean of total per bag

3 months (20 bags) (June)

6 months (20 bags) (Sept.)

9 months (20 bags) (Dec.)

12 months (22 bags) (Mar.)

21.45 ± 3.89

20.80 ± 4.70

95.10 ± 9.00

80.14 +_ 9.13

55.40 3.80 2.55 1.00 0.35

± 6.08 ± 1.52 -* 0.92 -+ 0.33 -+ 0.16

2.95 0.35 5.35 0.80 1.40

-0.15 _+ 0.11 0.05 8.45 0.50 0.30

± ± ± ± ±

0.54 0.16 1.41 0.26 0.41

-1.20 ± 0.30

± 0.05 ± 2.95 ± 0.17 _+ 0.29

0.70 21.60 0.30 1.60 0.20 0.05 0.65 5.70

--94.00 ± 9.23

± z ± ± • ± ± ±

0.25 3.61 0.14 0.60 0.09 0.05 0.20 0.98

60.05 ± 6.95

7.80 0.40 1.85 0.25 1.45

+- 0.83 +_ 0.19 +_ 0.46 ± 0.12 ± 0.41

9.32 1.32 1.73 0.18 0.45

± 1.68 +_ 0.76 +_ 0.72 _+ 0.08 ± 0.27

15.35 ± 2.47 3.35 ± 0.84

25.04 ± 6.55 2.00 ± 0.36

2.35 _+ 0.76 12.20 +_ 0.96 -7.75 ± 1.20 14.40 _+ 6.26 0.35 ± 0.16 4.85 ± 0.94 3.30 ± 0.68

2.32 +- 0.54 11.00 ± 0.96 16.50 4.54 0.14 13.59 20.27

168.45 +- 12.78

± 2.99 ± 1.48 +- 0.07 ± 1,30 +_ 2.90

188.54 -+ 12.13

TABLE 4 CHANGES IN ]'HE NUMBER OF INDIVIDUALSAND SPECIES (]'OTALS/20 SAMPLES) OF MOLLUSCA, ISOPODA, DIPLOPODA, ARANEAE, HETEROPTERA AND COLEOPTERA IN THE MONITORINGSERIES OF LITTER SAMPLES OVER A 12-MONTH PERIOD 1970-7 I. THE FIGURESFOR THE 22 BAGSTAKEN IN MARCH HAVEBEENADJUSTED

No. Species No. Species No. Species No. Species No. Species No. Species

Araneae Coleoptera Heteroptera Diplopoda Mollusca Isopoda

3months (June)

6months (Sept.)

9months (Dec.)

12months (Mar.)

169 5 429 22 76 2 0 0 0 0 6

433 22 416 38 7 I 4 2 13 3 32

244 25 1902 49 8 3 276 8 97 4 155

250 25 1600 58 26.3 2 88.1 8 270 6 363

1

4

4

4

Araneae T h e 169 s p i d e r s in t h e s a m p l e s a f t e r 3 m o n t h s c o n s i s t e d a l m o s t e n t i r e l y o f a d u l t s a n d y o u n g o f Xysticus cristatus ( C l e r c k ) ( 1 0 8 s p e c i m e n s ) , a n d i m m a t u r e (56).

X.

cristatus

aggregation.

is

It o c c u r r e d

a

common

grassland

species

which

showed

linyphiids marked

in o n l y 3 b a g s o u t o f 20 b u t r e c o r d e d t o t a l s o f 22, 54 a n d

34, r e s p e c t i v e l y . A f t e r 6 m o n t h s

t h e t o t a l o f 4 3 3 i n c l u d e d 129 i m m a t u r e

Lycosidae

264

ERIC DUFFEY

o f the g e n e r a Trochosa a n d Pardosa a n d 169 i m m a t u r e linyphiids. In the r e m a i n i n g 135 s p i d e r s 22 species w e r e represented, o f which O e d o t h o r a x f u s c u s (BI.), Oe. retusus (Westr.) a n d Savignya frontata (BI.) were the most frequent. All are c o m m o n a n d w i d e s p r e a d in g r a s s l a n d s as well as o t h e r habitats. Less c o m m o n species r e c o r d e d after 6 m o n t h s i n c l u d e d Walckenaera nudipalpis (Westr.) (1), W. vigilax (Bl.) ( l ) a n d Porrhomma convexum (Westr.) (2). A f t e r 9 m o n t h s the last three h a d increased to 12, 2 a n d 26, respectively a n d two a d d i t i o n a l , less c o m m o n , species were r e c o r d e d : Gongylidiellum latebricola (O.P.-C.) (5) a n d Meioneta beata (O.P.-C.) (1). Xysticus cristatus n u m b e r s had fallen to 4, lycosids to 41 a n d i m m a t u r e l i n y p h i i d s to 58. A t the end o f the 12-month p e r i o d the g r a n d t o t a l was a p p r e c i a b l y lower, a few species being lost a n d others g a i n e d but, in general, the s p i d e r a s s e m b l a g e not c h a n g i n g very much.

Coleoptera T a b l e 5 records the r e p r e s e n t a t i o n o f the 16 families o f C o l e o p t e r a f o u n d in the

TABLE 5 TOTAL NUMBER (PER 2 0 SAMPLES) OF INDIVIDUALS IN 16 FAMILIES OF COLEOPTERA REPRESENTED IN THE MONITORING SERIES OF LITTER BAGS. THE FIGURES FOR THE 2 2 BAGS TAKEN IN MARCH HAVE BEEN ADJUSTED

Carabidae Hydrophilidae Leiodidae Clambidae Silphidae Ptiliidae Staphilinidae Pselaphidae Elateridae Cryptophagidae Orthoperidae Lathridiidae Phalacridae Coccinellidae Chrysomelidae Curculionidae

3 months (June)

6 months (Sept.)

9 months (Dec.)

12 months (Mar.)

1 l ----8 --22 1 381 1 1 -6

7 23 8 --151 145 --l -3

133 45 ---1 1662

80.9 51.8 0.9 0.9 0.9 18. l 1307.2

2 l 73

Il

----

12.7

0.9 3

-0.9

40

-0.9 123.6

--

m o n i t o r i n g litter bags. A t the 3 - m o n t h stage beetles o f the families L a t h r i d i i d a e a n d C r y p t o p h a g i d a e were by far the most a b u n d a n t , but in the second half o f the 12m o n t h p e r i o d the S t a p h y l i n i d a e , C a r a b i d a e and C u r c u l i o n i d a e soon d o m i n a t e d the fauna. The H y d r o p h i l i d a e a n d Ptiliidae were also frequent. Nearly all the species r e c o r d e d d u r i n g the e x p e r i m e n t a l p e r i o d are c o m m o n a n d w i d e s p r e a d in Britain, including m a n y which are usually associated with d e c a y i n g v e g e t a t i o n and others which frequently o c c u r o n cultivated land. Several species are said to o c c u r in ' m a r s h y ' places a n d their presence in g r a s s l a n d on a h e a v y clay which s o o n b e c a m e w a t e r l o g g e d in wet w e a t h e r is p e r h a p s not surprising.

TRAMPLING AND GRASSLAND FAUNA

265

Heteroptera Only 3 species were recorded during the 12 months; Berytinus minor (H.-S.), present on all 4 sampling dates but most numerous at the 3-month stage; Drvmus sylvaticus (F.), recorded in December (1) and March (5) and Nabisferus (L.), a single specimen of which was found in December. Diplopoda None was recorded in the litter bags after 3 months. In September there were 2 species, represented by 3 specimens. One immature Polydesmus sp. was taken. In December at least 8 species were present and of the 276 specimens, 251 were immature Polydesmus sp. In March the latter were again most numerous, accounting for 78 out of the total of 97 millipedes in 22 litter bags. Isopoda After 3 months the woodlice were represented by only 6 specimens of Philoscia muscorum (Scop.), all occurring in one of the 20 litter bags sampled. The second set of samples, in September, included 4 species, but 27 out 0fthe total of 32 specimens were P. muscorum and, in addition, there were 3 Trachelipus rathkei (Brandt). The latter species, which is somewhat local in Britain, increased to 62 in December, and P. muscorum to 81. After 12 months P. muscorum had more than doubled, T. rathkei had maintained its numbers, and there was a big increase in Trichoniscus pusillus (Brandt), from 11 in December to 87 in March in 22 litter bags. Mollusca No snails were recorded after 3 months and only 3 species established themselves during the 12-month period: Vallonia excentrica Sterki, K pulchella (Mialler) and Vitrina pellucida (Miiller), all in small numbers. Slugs were also absent from the litter bags after 3 months. In September, 8 Arion hortensis F6russac and 2 Agriolimax reticulatus Miiller were recorded and in December the former had increased to 85 and the latter to 8. By the end of the 12-month period further increases of these species, to 219 and 54 respectively in 22 litter bags, were recorded, together with 2 specimens each of Arion ater (L.) and A. subfuscus (Draparnaud). Comparisons with the fauna of natural litter were difficult because of differences in structure, age, depth and chemistry. However, an estimate was made by taking 8 samples of natural litter in March 1971 (3 × 1 m 2 and 5 × 0.75 m 2 = 6.75 m 2) when the control litter bags were taken up. The total dry weight of the litter was 3,915 g and 527 animals were collected by heat extraction (excluding mites and Collembola). At this time the control litter bags scored a mean of 187.8 animals per bag and, if we assume that the average dry weight was 82 g, the comparable figure for natural litter was 11.00 animals. On an area basis (20 × 20 cm) natural litter scored only 3.10 animals compared with 187.80 in the litter bags. All the species recorded in the natural litter were also taken in the artificial litter where they were

266

ERIC DUFFEY

generally m u c h m o r e a b u n d a n t . Although. these figures c a n n o t be tested for statistical significance t h e differences were so g r e a t t h a t the artificial litter (after 12 m o n t h s ) was c l e a r l y a m u c h m o r e f a v o u r a b l e e n v i r o n m e n t for g r o u n d - l i v i n g g r a s s l a n d i n v e r t e b r a t e s t h a n the n a t u r a l litter. T h e m a i n r e a s o n m u s t be the g r e a t e r a m o u n t o f grass litter p e r unit a r e a in one c o m p a r e d with the other, a v e r a g i n g 82.30 g a n d 23.20 g d r y - w e i g h t respectively.

T H E EFFECTS OF T R A M P L I N G

ON THE F A U N A

T h e c h a n g e s in s t r u c t u r e a n d d e c r e a s e in d e p t h a n d v o l u m e o f the litter, the p e n e t r a t i o n o f soil into it a n d the p h y s i c a l i m p a c t o f t r e a d i n g , all c o m b i n e d to cause a r a p i d fall in n u m b e r s o f m o s t g r o u p s o f a n i m a l s r e c o r d e d . H o w e v e r , in spite o f this clear trend, n o t all g r o u p s r e s p o n d e d in the s a m e way. F o r e x a m p l e , there was no significant difference (by analysis o f v a r i a n c e ) b e t w e e n the n u m b e r s o f e a r t h w o r m s in t h e c o n t r o l s a n d t r e a t e d bags, n o r in the C o l e o p t e r a larvae, while D i p t e r a l a r v a e a c t u a l l y increased a n d were m o s t n u m e r o u s in the 10 t r e a d s / m o n t h litter bags, a l t h o u g h n o t s h o w n to be statistically significant ( T a b l e 6). In m o s t TABLE 6 DIFFERENCES IN THE FAUNA OF CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS, MARCH 1971. TOTALS PER 25 LITTER BAGS. ACARI AND COLLEMBOLA NOT COUNTED. THE TOTALS FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

Control litter bags

5 treads/ month

10 treads/ month

Significance of effect of treatment

Coleoptera Coleoptera larvae Heteroptera Hornoptera Hymenoptera Diptera Diptera larvae Thysanoptera Lepidoptera larvae Araneae Isopoda Diplopoda Chilopoda Mollusca Annelida

2003.4 233.0 33.0 43.2 4.5 11.3 626.1 50.0 58.0 275.0 412.5 113.6 3.4 339,8 506.8

349 109 -10 2 30 1032 42 24 75 12 5 -148 568

320 145 1 7 -5 1154 38 29 44 8 8 I ll3 452

p < 0.001 NS -p < 0.05 --NS NS p < 0.05 p < 0.001 p < 0.001 p < 0.001 -p < 0.001 NS

Totals

4713,6

2406

2345

N S --..not s i g n i f i c a n t

o t h e r g r o u p s there was a s u b s t a n t i a l fall in n u m b e r s b e t w e e n c o n t r o l s a n d treated bags a l t h o u g h the differences between the two levels o f t r e a t m e n t were small a n d n o t significant e x c e p t in the case o f spiders. It a p p e a r s t h a t the i m p a c t of treading,

TRAMPLING

267

AND GRASSLAND FAUNA

together with the modifications it brought about to the litter environment, were sufficient to cause great changes in the fauna, whether treading occurred at 5 or 10 times/month. At both levels of treatment the order of fall in total numbers compared with the controls was about 50% for the 15 groupings listed in Table 6 and 53.50% in the numbers of species of macroarthropods recorded. The higher numbers of Diptera larvae in the treated litter and the ability of earthworms to maintain their level of abundance probably indicated a response to the soil/litter mixture formed as a result of treading. This, coupled with poor drainage during wet weather, favoured those species which occur in mud enriched with organic material. For example, the increase in Hydrophilidae (Coleoptera) (Table 7) from controls to 10 treads/month was almost entirely due to the response TABLE 7

NUMBERS OF COLEOPTERA (TOTALS/25 LITTER BAGS) IN THE 6 BEST REPRESENTED FAMILIES RECORDED IN THE CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS, MARCH 1971. THE TOTALS FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

Carabidae Hydrophilidae Ptiliidae Staphylinidae Pselaphidae Curculionidae Total families/species recorded in each treatment

Controls

5 treads/ month

10 treads/ month

10I. 1 64.8 22.7 1634.I 15.9 154.5

24 52 -113 I 157

29 77 -75 136

12/58

6/31

6/29

of Helophorus brevipalpis Bedel (Table 8), a species of wet and muddy places (Balfour-Browne, 1958). The small carabid Bernbidion lunulatum Geoff. also showed a slight but not significant increase. Two species, Apion virens Herbst and Sitona lineatus (L.) (Curculionidae), showed little change in numbers between control and treated litter. They are both very common species, feed readily on clover (Trifolium repens L.) which was abundant in the grass ley, and are also known to overwinter in leaf litter (M.G. Morris, pers. comm.). They would appear to be relatively insensitive to treading. The spiders found in grassland litter are mostly small and fragile (1 - 3 mm). They hunt in the spaces between the leaf and stem fragments or construct tiny webs which would easily be destroyed by disturbance. The numbers/species recorded in the three treatments (per 25 litter bags) were: controls 275/25, 5 treads/month 74/12, and 10 treads/month 42/6. In this case an analysis of variance showed that there was a statistically significant difference (P < 0.02) between the two levels of treading as well as between these and the controls. The six most frequent species and the immature indeterminable Linyphiidae were all greatly affected by treading (Table 9), while three species showed little response. The numbers of two of the

268

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NUMBERS OF THE 21 MOST ABUNDANT SPECIES OF COLEOPTERA IN THE CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS, MARCH 1971. TOTALS PER 25 BAGS. THE FIGURES FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

Controls

5 treads/ month

Fall in numbers Amiseha analis (Grav.) Trachyporus hypnorum (Fab.) T. chrysomelinus (L.) Megasternum obscurum (Marsh.) Lathrobium longulum Grav. Euaesthetus bipunctatus (Ljungh) A theta ]ungi (Gray.) Pterostichus strenuus Panzer Lithocharis ochracea (Grav,) Xantholinus longiventris Heer Bembidion guttula Fab. Clivina Jossor L. Mycetophorus splendidus (Grav.) Stenus brunnipes Stephens Lathrobium .[ulvipenne Gray. Pterostichus vernal& Panzer Oxytelus rugosus (Fab.)

826.1 397.7 105.7 61.4 56.8 55.7 52.3 35.2 21.6 21.6 21.6 19.3 15.9 12.5 12.5 10.2 10.2

31 26 8 1 10 4 -3 -2 4 6 -13 1 1 2

Little Change in numbers Apion virens Herbst Sitona lineatus (L.)

25.0

31

13

119.3

116

117

1.1 6.8

51 8

72 15

Increase in numbers Helophorus brevipalpis Bedel Bembidion lunulatum Geoff.

10 treads/ month 18 18 2 1 13 3 -4 -5 7 1 -4 --3

l a t t e r were t o o low for c o n c l u s i o n s to be d r a w n but O e d o t h o r a x retusus, a small w e b - s p i n n i n g linyphiid, a p p e a r e d to have s o m e a b i l i t y to w i t h s t a n d the d i s t u r b a n c e a n d a l t e r a t i o n to the h a b i t a t caused by t r e a d i n g . All the species r e c o r d e d , a p a r t f r o m the f o l l o w i n g three, are w i d e s p r e a d a n d c o m m o n in d a m p g r a s s l a n d situations. C e n t r o m e r u s e x p e r t u s ( O . P . - C . ) (1 in the c o n t r o l bags) occurs o c c a s i o n a l l y in m o i s t g r a s s l a n d b u t is a t y p i c a l species of fens a n d m a r s h e s with p e r m a n e n t w a t e r l o g g e d g r o u n d . Gongylidiellum latebricola ( O . P . - C . ) a n d P o r r h o m m a c o n v e x u m (Westr.) are m u c h m o r e local species, s o m e t i m e s o c c u r r i n g in g r a s s l a n d b u t m o r e usually a s s o c i a t e d with d i s t u r b e d a r e a s a n d artificial e n v i r o n m e n t s such as cultivated land. F o u r specimens o f the f o r m e r o c c u r r e d in the c o n t r o l s a n d one in the 5 t r e a d s / m o n t h litter bags. T h e n u m b e r s o f the l a t t e r t a k e n are s h o w n in T a b l e 9. T h e w o o d l i c e ( I s o p o d a ) were r a t h e r m o r e sensitive to t r e a d i n g t h a n the spiders even t h o u g h they are p r i m a r i l y feeders on d e a d p l a n t m a t e r i a l a n d o t h e r o r g a n i c m a t t e r a s s o c i a t e d with it ( S u t t o n , 1972). N u m b e r s p e r 25 litter b a g s fell f r o m 412.50 in the c o n t r o l s to 11 a n d 8 respectively in the t w o levels o f t r e a t e d bags ( T a b l e 10). A r m a d i l l i d i u m vulgare (Lair.), Philoscia m u s c o r u m a n d Trichoniscus p u s i l l u s are all c o m m o n species b u t Trachelipus r a t h k e i is m u c h m o r e local a n d little is k n o w n

269

TRAMPLING AND GRASSLAND FAUNA

TABLE 9 NUMBERS OF THE MORE FREQUENT ARANEAE IN THE CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS~ MARCH 1971. TOTALS PER 25 BAGS. THE FIGURES FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

immature indeterminable Linyphiidae

Pirata hygrophilus T h o r e l l Pardosa amentata (Clerck) Dicymbium nigrum (BI.) Porrhomma convexum (Westr.) Lepthyphantes ericaeus (BI.) Bathyphantes gracilis ([31.) Oedothorax retusus (Westr.) Savignya./rontata (BI.) Xysticus cristatus (Clerck.) Totals

Controls

5 treads/ month

10 treads/ month

110,2 37,5 21,6 11.3 11,3 7.9 5.6

19 -1 8 ----

8 -2 -----

29.5 6.8 3.4

14 5 5

21 4 4

245.0

52

40

T A B L E 10 NUMBERS OF THE MORE FREQUENT ISOPODA IN THE CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS~ MARCH 1971. TOTALS PER 25 BAGS. THE FIGURES FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

Controls Armadillidium vu!gare (Latr.) Philoscia muscorum (Scop.) Trachelipus rathkei (Brandt) Trichoniscus pusillus (Brandt) Totals

10.2 231.8 71.6 98.9 412.5

5 treads/ month 9

10 treads/ month

I I

6 1 1

11

8

of its ecological preferences. All four species have previously been recorded in the neighbourhood of the experimental site (Harding, 1973). The slugs and snails (Mollusca) were each represented by 4 species respectively (Table 11), Arion hortensis and Agrolimax reticulatus were the first colonisers of the monitoring series of litter bags (after 3 months), increasing to fairly large numbers in March, and although numbers were lower in the treated bags they showed some resistance to treading. There was little difference between the numbers recorded in the two intensities of treatment. Both are very common species in grasslands and many other situations (Quick, 1960). Snails were much less abundant although the two most frequent species occurred in all the treatments. Vallonia pulchella is said to prefer moist fields and shady places while V. excentrica is found mainly in rather dry situations (Ellis, 1926). Nevertheless both species have been frequently recorded in grassland adjacent to the experimental site (Murrell et al., 1973). Lymnaea truncatula (Miiller) is a marsh

270

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T A B L E 11 NUMBERS OF MOLLUSCA (SLUGS AND SNAILS) 1N THE CONTROL AND TREATED LITTER BAGS AFTER 12 MONTHS, MARCH 1971. TOTALS PER 25 BAGS. FIGURES FOR THE 22 CONTROL BAGS HAVE BEEN ADJUSTED

Controls

5 treads/ month

10 treads/ month

Arion hortensis F ~ r u s s a c Agriolimax reticulalus M filler Arion ater (L.) A. subJuscus ( D r a p a r n a u d )

248.8 61.3 2.2 2.2

123 10 ---

106 13 ---

Totals

314.5

133

120

Vallonia pulchella ( M i i U e r ) V. excentrica S t e r k i V. pulchella/excentrica j u v s Lymnaea truncatula (Mt~ller) Vitrina pellucida ( M f i l l e r )

7.9 3.4 11.3 ---

5 2 6 1 1

2 5 5 1

Totals

22.6

15

Slugs

Snails

-13

and wet mud species and although only 2 specimens were taken, both occurred in the treated litter and not in the controls. Millipedes (Diplopoda) were not recorded in the monitoring series of litter bags until after 6 months. Only 4 specimens of 2 species were present in the 20 bags but, three months later in December, a total of 276, representing 8 species, was taken. In March the total (from 22 bags) had fallen to 97 and 7 species were present. Most of the March total were immature specimens and only 1 species (Brachydesmus superus Latzel) was represented in all treatments. Blower (1958) describes this species as 'commonly associated with farmland; the only polydesmid found habitually in the soil'. Polydesmus denticulatus Koch was the only other millipede for which several adult specimens were recorded. It is said that it sometimes occurs very commonly in deciduous woodland leaf litter on base-rich soil (Blower, 1958). It is abundant throughout the Monks Wood National Nature Reserve (Welch, 1973), which lies adjacent to the experimental plot, so it is possible that the large number of immature Polydesmus sp. specimens also included this species. The sharp fall (Table 12) from 109.80 specimens and 7 species in the controls (per 25 bags) to 8 specimens and 2 species in the 10 treads/month litter samples suggests a marked sensitivity to treading.

DISCUSSION

The experiment described relates only to the fauna of the litter component in the vegetation. In a natural situation litter accumulates within the living plant cover

TRAMPLING

AND

GRASSLAND

271

FAUNA

TABLE 12 NUMBERS OF D I P L O P O D A IN THE C O N T R O L AND TREATED L I T T E R BAGS AFTER 12 MONTHS, M A R C H 1 9 7 1 . TOTALS PER 2 5 RAGS. FIGURES FOR THE 2 2 C O N T R O L BAGS HAVE BEEN A D J U S T E D

5 treads/ month

10 treads/ month

88.6 9.0 5.6 1.1 1.1 1.1 1.1 1.1 1.1

--2 ----3 --

5 -3 -------

109.8

5

8

Controls Polydesmus s p . ( i m m a t u r e ) P. denticulatus K o c h Brachydesmus superus L a t z e l Polydesmus angustus L a t z e l P. gallicus L a t z e l lulus scandinavius L a t z e l Ophyiulus pilosus ( N e w p o r t ) Brachyiulus pusillus ( L e a c h ) lulus / Ophyiulus ( i m m a t u r e ) Totals

and treading would influence the fauna associated with both types of plant material. However, although the use of hay enclosed in nylon mesh bags as a substitute for litter does not closely represent conditions in nature, there is no reason to believe that the species present responded to trampling in a different way from the same species occurring in natural litter. In addition, the use of litter bags made it possible to obtain much larger numbers of animals per sample than would otherwise have been possible. The small differences between the numbers and species of animals recorded in the two intensities of treading was unexpected but may be due to the experimental site being situated on a heavy clay soil which soon became waterlogged and sticky in wet weather. In such conditions it is possible that comparatively few treads were necessary to compress the litter into the soil surface, resulting in a rapid change in structure and volume of the litter in both treatments. On a light, free-draining soil grass litter would remain drier, and so more resilient to the physical impact of treading, and greater differences between the faunas of the two intensities of trampling could be expected. The area covered by each litter bag was 20 × 20 cm but the rubber boots used in treading measured 31.50 cm in length and 11.00 cm at the widest point of the sole. Consequently, treading was unequally distributed and the least affected parts of the bags were probably the corners. In future work the measurements of the litter bag should more closely fit the shape of the boot and a parallel study on a contrasting soil type would help to illustrate whether or not this has an important influence on the response of treading. The effect of trampling intensity on the rate of litter breakdown in grassland is not known, although it is assumed that local conditions (vegetation and soil types, rainfall) have a considerable influence on this process. Burden (1970) found that in dry, hot weather trampling increased the amount of litter in a chalk grassland on a scarp slope because the dry vegetation was broken up by disturbance. This effect

272

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would be most marked in the late summer in grassland not previously used by the public but, where a short sward is maintained by regular treading throughout the growing season, the annual increment of litter is probably small. The results of the experiment described in this paper did not distinguish between the decline in animal numbers caused by changes in the litter habitat and the decline directly attributable to death by crushing. It seems likely that the former is more important. Such habitat changes seem to take place before there is a noticeable change in the growth form and species frequency of the living plants. This may account for the fall of over 50% in the numbers and species of animals after 120 treads/annum, whereas little or no change in the plant life of a chalk grassland was recorded after 520 treads/annum (A. Coker, pers. comm.). However Liddle (1975) reported that 384 passages on a dune grassland during the winter months reduced vegetation height by 55%. Published work on the response of living plants--mainly grasses--to trampling suggests that the treading intensities which can be tolerated before measurable changes occur (growth form and species composition of the sward) are far higher than for invertebrate animals. Trampling stimulates tillering in some grasses so that, although vegetation height may be reduced, a continuous green sward is maintained. When a grassland is kept short by grazing or mowing it has been shown that there is a significant fall in the numbers of species and population density of some invertebrate groups associated with living plants (Morris, 197 l). A similar effect can be expected when trampling reduces vegetation height by wear and, in addition, the litter fauna may decline by over 50%. Regulation of visitors to grassland amenity areas usually has the objective of reducing wear on the vegetation to levels at which a continuous green sward survives without signs of erosion. This maintains the visual attractiveness but the invertebrate fauna will be poor. The results of this experiment suggest that in areas with conservation interest visitor control should aim at setting aside zones where regular access is not permitted or a rotation of use is established so that certain areas are not continually subjected to trampling. SUMMARY

(1) The effect of trampling on the fauna of grassland litter was studied by using sterilised hay in nylon mesh bags placed in a 7-years-old grass ley for 12 months. Two levels of treading intensity: 5 treads and 10 treads/month, respectively, were used during the experimental period, together with an untreated control series of litter bags. A monitoring series of litter bags was also established to record the colonisation of litter by invertebrate animals at intervals of 3, 6, 9 and 12 months. (2) Natural leaf litter in the grass ley was scarce because an annual hay crop was taken each year after the grass was sown. Its fauna was poor compared with that in the litter bags and all the species recorded in it were also taken in the latter.

T R A M P L I N G A N D GRASSLAND FAUNA

273

(3) The change in structure of the litter after treading was assessed by embedding in gelatin followed by sectioning; a measurement of the proportion of air space to leaves and stems was made using a Quantimet Image Analysing Computer on the photographed sections. (4) After 12 months the volume of the control litter bags had fallen by 55.1% due to natural decay while the 5 treads/month bags fell by 68.40% and the 10 treads/month bags by 81.0%. The proportion of air space in the controls was 63.0%, in the 5 treads/month 54.0%, and in the 10 treads/month 38.0%. Treading also forced earth into litter bags, particularly during wet weather. (5) The overall effect of treading on the fauna was a substantial decline in numbers and species. Total numbers in the 10 treads / month (excluding Acari and Collembola) were just over 50% less than in the controls and the groups determined to species level (Araneae, Coleoptera, Isopoda, Diplopoda and Mollusca) fell by 53.50%. However, Diptera larvae increased in numbers and earthworms showed little change, probably because treading forced earth into the litter. (6) At the species level sensitivity to treading varied. Of 21 species of Coleoptera for which more than 10 specimens were recorded, 17 showed a sharp fall from controls to trampled litter (10 treads/month), 2 showed little change while 2 actually increased in numbers. This last response was most marked in Helophorus brevipalpis (Hydrophilidae), a species usually found in wet and muddy situations. Three species of spiders also showed a comparatively small drop in numbers, in spite of their fragility. All four species of Isopoda showed great sensitivity to treading. (7) Only small, non-significant, differences were recorded between the faunas of the two trampling treatments of 5 treads/month and 10 treads/month, with the exception of the spiders. (8) Many of the recorded differences in the fauna between trampled and untrampled litter, both increases and decreases in numbers, appear to have been caused by changes in the structure of the litter habitat (smaller volume, fewer air spaces, fragmentation of leaves and stems, creation of mud/litter mixture). These differences cannot be separated from the effect of the physical impact of treading which might have destroyed some species and not others. (9) There is evidence that the invertebrate fauna of grassland litter is affected by levels of treading much lower than those required to produce changes in the structure and species frequency of the living plants.

ACK NOWLEDGEMENTS

I am particularly grateful to Peter Fox for his technical assistance in constructing and working the gelatin embedding apparatus and to Peter Tinning for his invaluable assistance in determining the Coleoptera, Opiliones and other groups and in many other ways during the preparation of this paper. I would also like to

274

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t h a n k the f o l l o w i n g p e o p l e w h o h a v e h e l p e d w i t h the d e t e r m i n a t i o n o f c o l l e c t i o n s : P. M o r d a n , M. P. K e r n e y a n d P. W. M c D o n a l d ( M o l l u s c a ) , C. F a i r h u r s t ( D i p l o p o d a ) , P. H a r d i n g ( I s o p o d a ) , R. C. W e l c h , M. J. D. B r e n d e l l a n d M. G. M o r r i s ( C o l e o p t e r a ) , M. S k e l t o n ( L e p i d o p t e r a l a r v a e ) a n d H. K. K e n w a r d ( H e t e r o p t e r a ) . J o h n H u b b a r d p r o v i d e d v a l u a b l e a d v i c e o n t h e use o f the Q u a n t i m e t I m a g e A n a l y s i n g C o m p u t e r a n d the M e r l e w o o d R e s e a r c h S t a t i o n o f t h e I n s t i t u t e o f T e r r e s t r i a l E c o l o g y at G r a n g e - o v e r - S a n d s , C u m b r i a , m a d e t h e c h e m i c a l a n a l y s e s o n t h e h a y a n d litter s a m p l e s . I a m g r a t e f u l to J. P. D e m p s t e r , M. G. M o r r i s , M. J. L i d d l e a n d T. C. E. Wells f o r v a l u a b l e c o m m e n t s o n the manuscript.

REFERENCES ANDERSON, J. M. & HEALEY, 1. N. (1970). Improvements in the gelatine-embedding technique for woodland soil and litter samples. Pedobiologia, 10, 108-20. BALFOUR-BROWNF. (1958). British water beetles, 3, London, Ray Society. HAYFIELD,N. G. 0971). Some effects of walking and skiing on vegetation at Cairngorm. In The scientific management o f animal andplant communities for conservation, ed. by E. Duffey and A. S. Watt, 469-85. Oxford, Blackwell. HAYFIELD,N. G. (1973). Use and deterioration of some Scottish hill paths. £ appL Ecol., 10, 635-44. BLOWER, J. G. (1958). British millipedes (Diplopoda). Synopses Hr. Fauna, 11. BURDEN, R. (1970). Some effects of people on the Nature Trail at Ranmore, Surrey. The Surrey Naturalist, 1969. BURDEN, R. F. & RANDERSON,P. F. (1972). Quantitative studies of the effects of human trampling on vegetation as an aid to the management of semi-natural areas. J. appL EcoL, 9, 439-57. CHAPPELL, H. G., AINSWORTH,J. F., CAMERON, R. A. n. & REDFERN, M. 0971). The effects of trampling on a chalk grassland ecosystem. £ appL EcoL, 8, 869-82. ELLIS, R. A. (1926). British snails. Oxford, Clarendon Press. HARDING, P. T. (1973). Crustacea, Isopoda. In Monks Wood. A nature reserve record, ed. by R. C. Steele and R. C. Welch, 124-5. Huntingdon, The Nature Conservancy. JONES, MARGARETG. (1968). The effect of moving carabids on oviposition by frit fly (Oscinellafrit L.). Entomologist's Non. Nag., 104, 85-7. LIDDLE, M. J. (1975). A selective review of the ecological effects of human trampling on natural ecosystems. BioL Conserv., 7, (1) 17-36. MORRIS, M. G. (1971). The management of grassland for the conservation of invertebrate animals. In The scientific management o f animal and plant communities for conservation, ed. by E. Duffey and A. S. Watt, 527-52. Oxford, Blackwell. MURRELL, SALLY, LYTH, M. & MORDAN, P. B. (1973). Mollusca. In Monks Wood. A nature reserve record, ed. by R. C. Steele and R. C. Welch, 259-67. Huntingdon, The Nature Conservancy. PERRING, F. H. (1967). Changes in chalk grassland caused by galloping. In The biotic' effects o f public pressures on the environment, ed. by E. Duffey, 134-42. Monks Wood Experimental Station Symposium No. 3, The Nature Conservancy. QUICK, H. E. (1960). British slugs (Pulmon~ita: Testacellidae, Arionidae, Limacidae). Bull. Hr. Mus. nat. Hist., Zoology, 6, 196-226. SPEIGHT, i . C. n. (1973). Outdoor recreation and its ecological effects. A bibliography and review. University College, London Discussion Papers in Conservation No. 4. STREETER,D. T. (1971). The effects of public pressure on the vegetation of chalk downland at Box Hill, Surrey. In The scientific management of animal and plant communities for conservation, ed. by E. Duffey and A. S. Watt, 459-68. Oxford, Blackwell. SUTTON, S. (1972) Woodlice. London, Ginn & Co. WELCH, R. C. 0973) Diplopoda. In Monks Wood. A nature reserve record, ed. by R. C. Steele and R. C. Welch, 255-8. Huntingdon, The Nature Conservancy.