JANUARY - MARCH 1985 (no 972)


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N2853 > NH



A Quarterly Journal of Natural History for the North of England

Edited by M. R. D. SEAWARD, MSc, PhD, DSc, FLS, The University, Bradford


3 Studies on the Flora of Teesdale Margaret E. Bradshaw

23 The Population and Distribution of Nightjars (Caprimulgus

europaeus) on the North York Moors R. Leslie

29 Freshwater Microturbellaria from the English Lake District, including Three Species New to Britain J. O. Young

31 The Helminth Parasites of the European Eel, Anguilla anguilla (L.)

from the Driffield Canal, North Humberside /. C. Williams and

P. A. Bolton

37 Autumn Fungus Foray T. F. Hering

37 Spring Fungus Foray T. F. Flering

38 Hybrid Willows Eileen Bray

22, 30, 39 Book Reviews



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A Quarterly Journal of Natural History for the North of England

Edited by M. R. D. SEAWARD, MSc, PhD, DSc, FLS, The University, Bradford








Presidential Address to the Yorkshire Naturalists’ Union, Ilkley, 3. December 1983


‘A journey of a thousand miles begins with a single step’

In these introductory words of thanks to you, the Yorkshire Naturalists’ Union, for the honour you have bestowed upon me by electing me your President, I wish also to remember the Darlington and Teesdale Naturalists’ Field Club who provided me with the opportunity to meet Kit Rob soon after I migrated north over the Tees, and Kit herself, for her hospitality and exaggerated expectations of an ‘ignorant’ graduate and fledgling taxonomist and field-botanist which both flattered and encouraged me. It was Kit who suggested I join the YNU. As you know, my attendance at YNU meetings has been irregular, but I have valued greatly the friendships of several botanical members who happen also to have become Presidents: Eva Crackles, Joan Duncan and Max Walters. I was born near Driffield and went to Leeds University where long plant lists out of Tansley (1939) almost put me off ecology. I regret not taking the opportunity to visit Teesdale when I was a second-year student. Later, I did move to teach at Bishop Auckland because it was near Teesdale, which I had heard had an interesting flora. So began a series of botanical journeys.

The first started from a suggestion by Max Walters that I ‘look at Alchemilla’ in the Durham Pennines. There are advantages in being a novice in a strange land; one learns to use one’s eyes, being less blinkered than those who go fully primed with what to look for and where or with knowledgeable friends. My beginner’s luck was the discovery of a lady’s mantle new to Britain which Max determined as Alchemilla subcrenata (Walters, 1952). Obversely, I spent many fruitless days searching for A. gracilis , eventually found in Northumberland 25 years later by G. A. Swan. Now, I suggest someone look in moderately base-rich pastures in Teesdale instead of the meadow habitats I searched. By the end of the first summer, and with much help from Max in checking my near-weekly postal packages of leaves and inflorescences, I had learnt the nine critical Alchemilla species occurring in Teesdale. Max’s suggestion that I plot their distributions onto maps eventually resulted in a published paper (Bradshaw, 1962). So began my fascination with plant distributions and I had become knowledgeable in a plant group and the Teesdale ‘locality’. H. G. Baker, Max Walters and D. H. Valentine initiated the second journey, the pursuit of a Ph.D. at the University of Durham, and more papers in Watsonia (Bradshaw, 1963, 1964).

The third journey began in autumn 1964, when the Cow Green Reservoir project threatened to flood parts of the botanically famous Upper Teesdale. Suddenly, it became essential to know where the rare species grew in relation to the top-water-line of the reservoir (488 m; 1603ft O.D.). However, as with many other ‘assemblages’ and ‘localities’, many botanists knew one or more sites for each species but no-one knew the complete distribution of all of them. A detailed search and mapping programme was immediately begun by myself and friends, using improvised maps constructed from black-and-white aerial photographs (Meridian, 1956) as a base. In the light of our later work I am amazed at the completeness of our records of the vital data. The outcome of the reservoir proposal is well known. However, this ill wind stimulated me to expand the mapping into a research project, suitable for the students of the then Extra-Mural Department of the University of Durham, to map the distributions of the Teesdale Assemblage on the upper part of Widdybank Fell. Working two or three weeks each summer, we recorded some 21 members of the Assemblage and six other species in an area totalling 1 X 0.25 miles (1.6 X 0.4km); the project took ten years. The products of those hours of crawling over the often stony Teesdale fell, and evening paperwork in Langdon Beck Hotel and later, form the core of this address.

Naturalist 110 (1985)


Studies on the Flora of Teesdale

For two-and-a-half centuries the Teesdale locality has attracted people interested in plants to see and add to the Teesdale Assemblage that ‘unorganized grouping of plants or animals occurring in a particular locality’ (Poore, 1964). By 1950, when I ‘discovered’ Teesdale, published data were in old Floras and plant lists or thinly scattered elsewhere. In 1954, Pigott and Walters included Teesdale in a paper seeking to explain the phenomena of ‘assemblages’ and ‘localities’, and in 1956 Pigott published the first paper on the vegetation of Upper Teesdale. Since 1956 studies have multiplied, and can be traced in the collective works on the natural history of the area edited by Clapham (1976) and Bradshaw (1976). The former is essential background reading to this paper.

Recent work (Johnson, Robinson and Hornung, 1971) on the origin of the meta- morphosis of the Melmerby Scar Limestone to crystalline marble in Teesdale indicates some contributory factors: the intrusion of the Whin Sill is at the lowest level in the strata; here it is at its thickest, and the limestone is pure. Darker limestones with free carbon have not metamorphosed. Weathering of the marble is now thought to have mostly taken place below ground at the junction of drift and limestone under the influence of percolating water and roots. When the drift erodes, rotten marble is exposed which rapidly breaks down to the familiar loose calcite sand (‘sugar limestone’). The types of soil which have developed on the Fell have been shown (mainly by Hornung) to be related to the depth and nature of the deposits over the bedrock and to their water regime. Over the marble, the following develop according to the depth of the drift: over 60cm - podzols, peaty gleys and deep peats; 30-60 cm - brown-earths, calcareous brown soils and calcareous gleys; under 30cm - rendzinas. These last are subdivided: rendzina a is formed in situ on the rotten crystalline marble; rendzina (3 (the most widespread) is a complex of drift and rotten marble, and rendzina 7 is formed in areas of aeolian erosion and accretion as on Cronkley Fell, All these rendzinas are characterized by alkaline reaction and excessively free drainage so that a water-deficit develops after even short dry periods (Welch and Rawes, 1969).

Finally, Alison Jones’s phytosociological study of the vegetation of Widdybank Fell (Jones, 1973) is a most valuable contribution towards understanding the distribution of the mapped species. I am greatly indebted to her for permission to draw liberally on her thesis and that part of her work published as a booklet and vegetation maps at the scales 1:10000 and 1:2500 (Bradshaw and Jones, 1976). She analysed complete plant lists from over 550 representative sample plots1 of the vegetation of the whole Fell, and grouped them into the communities (‘mapping units’) which form the basis of the maps. Habitat features of aspect, slope and vegetation cover were recorded for each plot, and Hornung provided descriptions and analyses of the soils. Outlines of the phytosociological method, and general descriptions of the vegetation of the Fell appear in Bradshaw (1976) and Clapham (1976). Precise characterizations of the mapping units are available in Bradshaw and Jones (1976).

Correlation of the species-maps with the vegetation-maps and Jones’s thesis has provided much ecological information about each species and its affinities within the vegetation classification of the phytosociologists to put beside my own field experience. Jones found that 60 per cent of the Teesdale Assemblage species on Widdybank Fell (Table 1) are diagnostic species or frequently present in either the short, freely-drained limestone grasslands2 or the calcareous flushes and short-sedge-marshes;3 several of them belong similarly to two corresponding arctic-alpine vegetation types4,5 in continental Europe. Most of the remaining 40 per cent are diagnostic of the vegetation types of old lead-mine spoil, springs with calcareous water, and acidic grasslands on damp soils.6,7,8 Two species, Plantago maritima and Armeria maritima are usually characteristic of coastal saltmarshes9, but also occur in inland habitats. In addition, several of the species are frequent in the man-influenced, ‘neutral’ grassland10 and in the acid rush- and short- sedge-marshes.11

In the following pages the mapping units are referred to by the numbers used in the booklet and the maps (e.g. m.u.5), and the frequency of the species as determined by Jones on the scale I to V. 2


Studies on the Flora of Teesdale Distribution of the Plant Species The area of Widdybank Fell searched by the study-groups is shown in Fig. 1. It comprised the calcareous grasslands, flushes and short-sedge-marshes and associated communities overlying and influenced by the sugar limestone and base-rich drainage water on the west, south-west and south slopes of the Fell including part of the reservoir basin, and the unaltered Robinson limestone which forms a small plateau east of the Track, south of Slapestone Sike. Sample areas only were searched: (a) on the Robinson limestone, (b) immediately south of the meteorological station and (c) on the heather-covered upper part of the limestone escarpment to the south. Jones’s vegetation map (1:10000) shows a much larger area of the ‘dry’ communities (coloured pink, yellow and the adjacent pale green) than of the ‘wet’ communities (blue) which are especially scarce in the south-east of the surveyed area. The Slapestone Sike area to the north-west is isolated from the remainder by blanket-bog covering the sugar limestone escarpment and the Whin Sill, and by the suitable ‘wet’ communities being destroyed by the construction of the access road before the mapping commenced.

Examination of the distribution maps of the 25 members of the Teesdale Assemblage of this survey shows they can be divided into three groups: (a) those predominantly of the drier habitats, (b) those of the wetter habitats and (c) those which occur frequently in both drier and wetter habitats.

1. In the dry habitat group the most widespread and frequent are: Gentiana verna. Polygonum viviparum, Antennaria dioica (Fig. 3) and Galium boreale (Fig. 4); Potentilla crantzii (Fig. 2) is equally widespread but of much lower frequency. Initially the Gentiana and Polygonum were not recorded because I believed them to be ubiquitous in the study area; consequently we lost some of the finer detail. Conversely, the mapping of Kobresia simpliciuscula and Carex capillaris was discontinued because they can be mapped more quickly from their autumn leaf colours (though to date the maps are incomplete). J uncus alpinus proved too difficult to identify with certainty from the immature fruits in July. Gentiana verna and Polygonum viviparum are indeed almost ubiquitous in the freely- drained limestone grasslands (m.u.1-7; on rendzinas, calcareous brown soils and brown-earths), and in the related man-influenced, ‘neutral’ grasslands (m.u. 19-21; on slightly more acidic, gleyed brown-earths) which contain many synanthropic species {Beilis perennis, Prunella vulgaris. Ranunculus acris) and lie adjacent to the Track. Nevertheless, there are some differences between the two species.

Gentiana verna is absent from the driest communities (m.u. 1/2) on or around the eroding sugar-limestone edges where the almost humus-free shallow rendzina soils are subject to extreme xeric conditions (Park, in Welch and Rawes, 1969). Jones gives it a high frequency (IV) (see Table 1) in the dampest grassland (m.u. 7), which can occur on all the calcareous soil-types. It is usually absent from the wet communities, though it can be found on the drier parts of hummocks. Apparently the gentian avoids the extremes of soil moisture. It can tolerate the competition and light shade produced by the low shrubs of heather in m.u. 4, where it is probably rooted below the somewhat acidic surface litter.

Polygonum viviparum has a distribution which is very similar to but wider than that of Gentiana verna. Where records were made on the escarpment, which included much of the heather grassland (m.u. 4), it rarely failed to appear. Unlike the gentian it occurs


Phytosociological terminology:

1 Aufnahmen, 2 Seslerio-Mesobromion (m.u.1-7), 3 Caricion davallianae (m.u. 8, 9, 11- 14), 4 Kobresio-Dryadion (Elyno-Seslerietea), 5 Caricion bicoloris-atrofuscae (Tofieldie- talia), 6 Violetea calaminariae (m.u.V), 7 Cratoneurion (Montio-Cardaminetea)

(m.u. A), 8 Nardo-Callunetea (m.u. 25, 32, 33), 9 Asteretea tripolii, 10 Ranunculo- Anthoxanthion (m.u. 19-21), 11 Caricion curto-nigrae (15,16), 12 Constancy value.

6 Studies on the Flora of Teesdale


Studies on the Flora of Teesdale


Fig. 3 Fi9*

Viola rupestris / Viola rupestris x riviniana


Studies on the Flora of Teesdale


Studies on the Flora of Teesdale

occasionally on the driest sugar limestone (m.u.1/2) but was unrecorded in the wettest (m.u.7). It has a low frequency in the very similar m.u.8 and the turfy marshes (m.u.ll) where the hummocks provide suitable sites; the maps show it to be frequent in a complex of flushes and drier communities at the east end of the area. Its ability to tolerate some trampling almost certainly accounts for its high frequency (III) in communities (mainly m.u.21) adjacent to the Track. Somewhat surprisingly this species is very sparse on the Robinson limestone where the gentian is frequent in all the sampled areas.

Antennaria dioica (Fig. 3) and Galium boreale (Fig. 4) appear to have broadly similar distributions. Both species are inconspicuous in the sward, the former because of its low, prostrate habit and the latter because of its short brownish-green erect shoots, which are tall only amongst plants such as heather. Sheep quickly remove the sparse inflorescences of Antennaria dioica so fruit is rarely found; cultivated plants from the reservoir basin revealed a remarkable range of red, pink and white colour forms in the male inflorescences. I have never seen the bedstraw in flower on the Fell, except on the rocks at Cauldron Snout. Both species spread vegetatively, A. dioica forming smallish dense patches and the Galium forming more dispersed larger clones. Jones’s frequency values appear to be rather low (Table 1). Antennaria dioica has the denser distribution, in a slightly wider range of communities, favouring the drier habitats including the open shallow rendzina soils of m.u.l and 3. It is most frequent in the widespread and species-rich m.u.5 and closely-related m.u.21, and only slightly less frequent in the heather grassland (m.u.4). It is sparse in communities with much Kobresia (m.u.6,7), with whose stiff, erect stems it may be unable to compete. In contrast, Galium boreale is absent from the driest soils (m.u.1/2) and from m.u.6. Its main distribution is in the widespread communities on the brown-earths and brown calcareous soils (m.u.4, 5, 21) and in m.u.20 (of the man-influenced, ‘neutral’ grasslands) which occurs as hummocks in the damp calcareous grassland of m.u.7. It is more frequent than Antennaria dioica on the Robinson limestone.

Potentilla crantzii (Fig. 2) is another inconspicuous species which is very thinly dispersed throughout much of the grassland on the sugar limestone (m.u.3,4,5,6). None was found on the Robinson limestone, though it is known from unaltered limestone and Whin Sill outcrops in the wider Teesdale area. Only once have I seen it in flower and once in fruit on the Fell.

These first five species are predominantly plants of the more closed communities, including the most widespread of the freely-drained limestone (m.u.5) and the man- influenced, ‘neutral’ (m.u.21) grasslands. The next group of species have high frequencies in the more open, dry habitats associated with the eroding sugar limestone: Viola rupestris, V. rupestris X riviniana , Carex ericetorum , Plantago maritima and the more local Draba incana. Minuartia verna belongs to this group (Table 1), but for some reason now forgotten was not included in the mapped species.

Viola rupestris (Fig. 5) is the next most widespread and frequent species; it has been recorded in all the freely-drained limestone grassland communities except that dominated by heather (m.u.4). Though not rhizomatous the plants occur in fairly dense colonies as well as small groups and isolated individuals. Distribution on the Fell is in large and small disjunct patches, which more-or-less coalesce towards the south-eastern end of the limestone. Jones gives it high values (V and III) in m.u.l and 2, but, in my experience, her value (I) is too low in m.u.5 and 7, and particularly so in some areas of m.u.3 and 6. When looking at the total distribution on the Fell it appears possible that each major disjunct colony had its origin on or around the bare eroding limestone (m.u.1/2). It is known that flower production is inversely correlated with the percentage cover of the plant community (Bradshaw and Doody, in Clapham, 1976) and that plants in the open habitats (m.u. 1/2,3) produce the most chasmogamous flowers, whose capsules are borne on longer peduncles than the small self-pollinating cleistogamous flowers. The explosive discharge from the elevated capsules would have facilitated seed dispersal from these centres (m.u.1/2). This view is supported by the observation that areas of closed grassland (m.u. 5, 6) and isolated or large tracts of disturbed grassland (m.u.3) where V. rupestris is


Distribution of some Teesdale Assemblage species in the mapping units


Studies on the Flora of Teesdale

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Studies on the Flora of Teesdale 1 1

absent are distant from open eroding sites (m.u.1/2). Nevertheless the violet is absent from a few areas of apparently suitable habitats where the slope is gentle and the eroded edges shallow. Could these sites be too recent in origin? Plants are scarce on the sugar limestone furthest away from its contact with the Whin Sill and absent from the Robinson limestone.

Viola rupestris X riviniana (Fig. 6) is a sterile hybrid which spreads vegetatively by root-shoots and does form very dense colonies. It was recorded in a number of more or less discrete patches, mainly at the north and south ends of the sugar limestone escarpment. Close comparison of the species- and vegetation maps shows the hybrid to be concentrated in m.u.1/2, but I know it avoids the eroding edges and extends into the adjacent more closed communities of m.u.5,6,3,21 and vegetation which contains Calluna and Empetrum. The major colonies are very dense, between 2 and 5 metres in diameter, and each may be a single clone. The single plants and very small colonies (small dots on the map) may be the beginnings of new clones or plants which have not inherited the capacity of the V. riviniana parent to reproduce vegetatively. Established clones frequently occupy a habitat which is intermediate in character and position between the extreme m.u.1/2 of V. rupestris and the denser, closed communities in which V. riviniana is common. Lack of such habitats near the base of the escarpment may explain the absence of the hybrid between the Track and the southern records. Most of the isolated small colonies are at the lowest edge of the limestone escarpment in the transition zone between the limestone grassland and calcareous sedge-marsh communities an ecological niche which may favour a hybrid taxon. Hybrids from the reservoir basin grown in Teesdale soil at Durham exhibited much hybrid vigour.

Carex ericetorum (Fig. 7) is a rhizomatous sedge which forms locally dense clones of more-or-less evenly distributed shoots. It is always associated with the eroding sugar limestone (m.u.1/2) in the lower part of the strata. Like Viola rupestris its distribution is disjunct but more contiguous in the southern part. It is much more restricted, occurring mainly around the bare limestone patches. In one area a large dense colony extends from the edge of an eroded area into the closed and/or taller vegetation with heather or Kobresia, possibly indicating tolerance of slight shade. The soils are rendzinas or calcareous brown-earths. In a few places on the exposed edge it is associated with Rhytidium rugosum, a Teesdale Assemblage bryophyte. On Cronkley Fell it is widely dispersed through the drier limestone grassland communities of the summit plateaux. Here, but not on Widdybank Fell, on the shallowest soils it forms circular tufts and rings as in the Breckland. Could this habit be induced by soil-moisture stress? Teesdale plants, but not Breckland, are winter green. Winter photosynthesis may be important at this northern edge of the species’ range, as flower production can be much reduced by severe winter or early spring conditions when the distal part of the leaves of the monocarpic flowering shoots may be so extensively killed that the starved inflorescences produced only one male spike in contrast to good years when one male and two-three female spikes are produced. In most years fruit is produced, though much seems to be lost before maturity, maybe eaten by sheep or stripped between their divided hooves.

Plantago maritima (Fig. 9) in Teesdale is found in both very dry and wet sites. This pattern of distribution along water courses and eroding limestone in the lower part of the strata is clear. Though most common in the more basic, wet communities (see below), it is frequent in dry communities with open ground and grassland with 10 per cent or more of exposed soil (m.u.1/2, 5, 6), and the community of the open-cuts and spoil heaps from the lead workings (m.u.V). This latter can be clearly seen along Rods Vein. The highest frequency (IV) is in m.u.6 which can have open pockets and rendzina soils. Jones gives a moderately high frequency (III) in m.u.3 and 4 and 21. Close scrutiny of the distribution suggests that Plantago maritima is a primary coloniser of open habitats. It was seen in this role on quarry floors and spoil on the magnesian limestone of east Durham. Like Viola rupestris it can colonize the rendzina a soils but it maintains its position less well as the soil develops and the community becomes closed (e.g. m.u.5). The only records of high density in closed turf on a dry rendzina soil are from a small area (10-12 sqm) in a

12 Studies on the Flora of Teesdale

Fig. 7 Fig-

Studies on the Flora of Teesdale


Fig. 9 Fig. 1 0

14 Studies on the Flora of Teesdale

pre-myxomatosis rabbit warren, suggesting the original colonization was probably about 25-30 years ago. The other locations of high density are in the ‘neutral’ grassland (m.u.21) adjacent to the Track where trampling has opened up the turf and the plantain, like Polygonum viviparum, tolerates the disturbance and dry-flushing from the Track. Predictably, the plantain is absent from large areas on the Robinson limestone where the soils and communities appear too mature and closed; but its absence from all but one of the open-cuts is surprising as the high density of plants in the flushes around the edge of the plateau could have provided seed for colonization of the new bare ground.

Draba incana (Fig. 8) is much more localized than I expected. It is most frequent on the spoil and open-cuts of the mineral workings (m.u.V) and occasionally on moss, and in m.u.1/2 on soils which include rendzina a and y on redistributed calcite sand. Jones records it in more closed communities (m.u.3,5,7), where in my experience it always occupies bare soil eroded mole-hills and very small pockets which may be collapsed sub-surface mole-runs. Its distribution is disjunct, with comparatively isolated populations occupying natural habitats on bare limestone and shallow rendzina soils and ledges on ordinary limestone as in the open-cuts on the Robinson limestone and outside the survey area. In the north, the larger number of records is in part due to the presence of eroding limestone, the only extensive area on this Fell where moles create sub-surface runs, and many worked veins and spoil-heaps, especially Rods Vein, which have provided additional habitats in which large populations of Draba have developed. D. incana is a short-lived monocarpic perennial, whose population size is known to have fluctuated considerably between 1968 and 1976. It may be more at risk on Widdybank Fell than is generally realized. It is much more common on Cronkley Fell, especially on the redistributed sugar limestone (rendzina y) where its behaviour can be observed and could be recorded in a habitat-stabilization experiment in the Thistle Green exclosure.

Polygala amarella was for some time thought to be confined in Upper Teesdale to Cronkley Fell, but I have known it on Widdybank Fell since 1957. It is present as a small number of more-or-less disjunct colonies along a short stretch of the sugar limestone escarpment. It shows some preference for m.u.6 and is also present in m.u.3, 4 and 5 in semi-open and closed grassland including short plants of heather and crowberry. It is more tolerant of light shade than many of the Teesdale Assemblage rarities. In these relatively small colonies the number of individuals can be several hundreds but the species is a short-lived perennial and the numbers in monitored populations have changed alarmingly from high to very low (though now increasing again) over the last 15 years. During the mapping project an isolated plant was recorded on a sheep track some 200 metres from the nearest population, but several later searches have failed to refind it.

2. The species with wide distributions in both wet and dry habitats are Plantago maritima , Thalictrum alpinum and Primula farinosa. All three are more widespread than the other mapped species of the calcareous flush and short-sedge-marsh communities (m.u.8,9, 11-14) and all occur in the drier communities, especially those of the freely-drained limestone grassland group as well as several other communities and vegetation-types.

Plantago maritima (Fig. 9) was recorded by Jones in the highest number of communities (23) of all the Assemblage species (Table 1). Its occurrence in the drier communities has been considered above. It is most frequent in the highly calcareous, flushed communities of m.u.7 and 8 (pH 7. 5-8.0) which may be hummocky with some open ground and on a range of soils from rendzina 0 to calcareous gleys. Almost similar frequencies occur on the more acidic (pH 6. 0-7.0) damp, calcareous, peaty gleys of the man-influenced, ‘neutral’ grassland (m.u. 19,20), which often occur in the base of open-cuts, and where the plantain has low frequencies on the sides and edges (m.u.V). It is frequent in all the gravelly flush and short-sedge-marsh communities (m.u. 9, 14; 11,12,13) but less common in the closely related, slightly taller and more acidic (pH 5.5) but species-rich Calluna-Erica tetralix community (m.u. 25) and in springheads (m.u. A). Obviously the plantain favours open habitats, both dry and wet, e.g. m.u. 1/2,9 and 14. Maybe the greater soil moisture enables

Studies on the Flora of Teesdale 15

it to survive in the more closed, short-sedge-marsh communities (m.u.7,8,9pp, 12,13); whereas the greater acidity of the peaty gleys and shade from the taller vegetation (m.u. 15,16,25) reduce its frequency.

Thalictrum alpinum (Fig. 14) is most common in the wet vegetation complexes which overlie the Whin Sill below the Sand Hill on both sides of the Track and in the zone between the lower part of the sugar limestone escarpment and the bogs to the south. Occurrences of T. alpinum towards Tinkler’s Sike and in the lower Slapestone Sike areas, below the Access Road to the dam, are outside the surveyed area and consequently are missing from the distribution map. Its absence from the rest of the Slapestone Sike area, though slightly surprising, is real. It has slender rhizomes and though the shoots are usually dispersed it can form very dense patches, especially in moss-based communities. Comparison of the species-map and the vegetation-maps and Jones’s records show that the species usually have low frequencies in a slightly odd array of 16 mapping units in six separate vegetation-types. It is most frequent in the Calluna-Erica tetralix community (m.u. 25(H)), and complexes of that, with the sedge-marsh communities (m.u. 9, 12 and 8), all of which have wet, gleyed and sometimes peaty soils. It occurs also in communities on progressively drier calcareous and slightly more acidic mineral soils in the freely-drained limestone grasslands (m.u. 7, 6 and 4). Many of these communities are marginal in their vegetation-type and close to another, e.g. m.u. 7 and 8, 16 and 13, 4 and 32, 5 and 21. Although Thalictrum alpinum does grow in quantity in some pure stands of single communities, much of its distribution is in the transitional zones between vegetation- types; this is clearly seen by its frequent occurrence in the zone between the base of the limestone escarpment and bogs over the Whin Sill towards Tinkler’s Sike and lower Slapestone Sike. Both zones are enriched by in-washed calcite crystals, especially so from the Rod’s Vein adit and adjacent sugar limestone spoil-heap. In both of these areas Juncus alpinus another Assemblage species has high frequencies. Ecologically, Thalictrum alpinum avoids the most open habitats (m.u.l/2,9pp,14) and is exceedingly rare in m.u. 3 which has a shallow rendzina soil and the widespread closed limestone grassland (m.u. 5). The absence of Thalictrum from the entire Slapestone Sike area from immediately above the base of the escarpment (and Access Road) is difficult to understand in view of its occurrence on the escarpment to the south and its high frequency below the Road; perhaps the flushing caused by the outwash from the Rods Vein adit and spoil has enhanced its density there. It can tolerate light shade as it is found in heather and the taller rush- and sedge-marsh (m.u. 16). On the Fell it flowers regularly, though I have seen seed only once.

Primula farinosa (Fig. 10) is one of the most familiar species of the Assemblage. Primarily it is a species of the wet habitats, as can be seen in the map which identifies the calcareous springheads, flushes and wet communities thoughout the surveyed area, including the flushes on the edge of the Robinson limestone. It is present in all the flush and short-sedge-marsh communities and wettest calcareous grassland; the highest frequencies being m.u.7,ll(V), 8,12(IV) and 14(111); P. farinosa is also in the related Calluna-Erica tetralix hummocks of m.u. 25. The field survey revealed isolated single or small groups of plants in the freely-drained limestone grasslands; frequently these are in small patches in the wettest and the Kobresia- rich turf (m.u. 7, 6) but others are in the relatively dry m.u. 5 and 21. In these sites the individuals are long-lived and the population turn-over is low. The Primula has not been found amongst heather (m.u. 4), nor on the mine-waste (m.u.V). In most years it flowers well but seed production is low; I believe the scent of the open flowers attracts the sheep which remove a high proportion from all but the tussocky communities, where the grazing is incomplete, and swards where the stiff Kobresia shoots give some protection (e.g. m.u. 6). This was demonstrated in an area with Kobresia where fruits ripened regularly before horses grazed off the stiff shoots and enabled sheep to graze easily: now no fruits mature. Overall, sufficient seed ripens to maintain the population.

3. The wetter habitat group contains four species which are widely distributed in these sites across the Fell: Tofieldia pusilla (Fig. 11), Juncus triglumis (Fig. 12), Equisetum


Studies on the Flora of Teesdale

Fig. 1 1 Fig. 1 2

Studies on the Flora of Tees dale 17

variegatum and Saxifraga aizoides (Fig. 13). All are less widespread than the comparable ‘dry habitat’ group because of the smaller area of wet habitats in the survey area. Though differing in quantity, the distribution patterns of the first three appear to be very similar, but superimposition of the maps does reveal differences. Juncus triglumis and Saxifraga aizoides are restricted to open communities usually with running water, Tofieldia pusilla and Equisetum variegatum can occur in closed communities; Saxifraga aizoides is the least common on the Fell top. (At some stage data on the distribution of the Primula , Equisetum and Saxifraga in the flushes immediately east of the Track and along Red Sike have been lost. A recent inspection confirmed all three species to be present.)

Tofieldia pusilla (Fig. 11), like Primula farinosa, hugs the calcareous water courses and flushes and is intermediate between that species and Juncus triglumis in the total area, density and range of communities in which it occurs. It is present in all the calcareous flush and short-sedge-marsh communities except one (m.u.13), being most frequent in those which are hummocky (m.u.ll(V)) or form hummocks and hollows and complexes with other communities (e.g. m.u.8 and 12 with 9); it is also frequent in the lawn-like forms of m.u.8 and 9 and in m.u.7 of the limestone grassland. It is rarely ever found on bare substrate (as is Juncus triglumis ) and has low occurrences in the gravelly flushes (m.u.14, 9pp) where it grows on tussocks of other species. Like the Primula it is in the closely allied m.u.15 and 25, and in m.u.20. The species is most frequent in the Slapestone and Red Sike areas, becoming even scarcer in apparently suitable communities in the south. Isolated fans of leaves or small clumps have been found on the escarpment and in one spot on the Robinson limestone. Like the Primula , it fruits more successfully in the hummocky communities, as its inflorescences are also pulled out by the sheep.

Juncus triglumis (Fig. 12), though almost as widespread as the Tofieldia , occupies a narrower range of habitats and is even scarcer in the south, though it is known to be present outside the surveyed area in Tinkler’s Sike. It is fairly frequent, sometimes very frequent, in the open muddy, silty parts of gravelly flushes and rooted in cracks in rocky stream beds (m.u.9(IV)); it has a low occurrence in the sometimes open hummocky, short-sedge-marsh (m.u. 8(1)) but is rarely found in closed communities on the Fell. Juncus triglumis appears to have the narrowest ecological range of the Assemblage on the Fell top. It is dependent on a high water table and maybe on moving water; flower production and plant survival are seriously reduced by drought or changes in the course of the water flow. In most years it flowers and fruits freely, though young fruits appear to be eaten by birds.

Equisetum variegatum is much less frequent than Tofieldia pusilla , being about as common as Juncus triglumis with