LATE-GLACIAL MOSS RECORDS FROM THE ENGLISH LAKE DISTRICT DATA FOR THF STUDY OF POST-GLACIAL HISTORY

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1 LATE-GLACIAL MOSS RECORDS FROM THE ENGLISH LAKE DISTRICT DATA FOR THF STUDY OF POST-GLACIAL HISTORY BY W. PENNINGTON (MRS. T. G. TUTIN) University Department of Botany, Leicester {Received 3 May 1961) (With I figure in the text) The Late-glacial deposits of Windermere, Esthwaite Water and Ennerdale Water have already been described (Pennington, 1943, 1947, 1959; Franks and Pennington, 1961). In these and the other Lake District lakes so far investigated, there is clear stratigraphical definition of the boundaries of the three stages of the Late-glacial period, the pollen zones I, II, and III. Zone II, representing the temperate stage of the climatic oscillation, is represented by detritus silts and muds of variable organic content, lying on the inorganic laminated clay of zone I, and overlain by inorganic deposits of zone III, the period of the last, corrie glaciation. In the lakes whose drainage basin includes high corries which lay above the zone III snow-line (Manley, 1959), the zone III deposit is an inorganic laminated clay, but in Esthwaite Water, the whole of whose drainage basin lies below 1000 feet, the zone III deposit is a stony solifluction clay containing occasional plant remains. Most of the following moss records come from the deposits of Low Wray Bay, on the western shore of the North Basin of Windermere. A complete pollen diagram for the Late-glacial deposits at this site has been published by Godwin (i960), and a radiocarbon date of 992O± 120 B.C. assigned to a sample of the organic detritus mud of zone II. Zone I Fontinalis sqiiamosa L. Fig. i a-c. Zone I only This moss of fast-fiowing streams is very widely distributed in Windermere in the clay deposits between the top of the basal laminated clay and the detritus silt of zone II. It commonly occurs as leafiess stems (Pennington, 1947). These frequently occur in definite layers in the clay, and constitute the oldest organic remains in the lake deposits. Similar leafless stems were found at the same horizon in the deposits of Coniston Water, and stems with leaves attached in Ennerdale Water. The large diatom Melosira arenaria, which is very characteristic of this horizon in all the lakes, has been recorded as an epiphyte on this moss (Round, 1957). Polytrichum alpinum L. (Fig. 13 in Pennington, 1947). Zones I and III This moss of mountains and moorlands above 1500 feet is readily identifiable by the form of the apical cells of the lamellae. Leaves occur in the clays above and below the organic silts of zone II. 28

2 Late-placial mosses 29 Rhacomitrium fasciculate Brid. Zones I and II This moss, characteristic of mountain rocks, has been recorded from zone I in several cores from Windermere, but is more common in zone II. The absence of a hyaline point and the form of the cells distinguish even detached leaves from other species of Rhacomitriiim, but many specimens show in addition the characteristic mode of branching. Hypnuni sp. Occasional. Fig. I. a-c, Fontinalis squamosa; Ennerdale Water, Zone I. a, leaf (not entire) / 10; b, areolation at angle, 67; c, habit/3.3. d-g, Pseudoleskea patens ;'VJm(i<iTU\(f!:e, Zone II; d, habit : 40; e, leaf X 67; f, areolation along the line XX (m = curled margin); g, single cell (y in f) in profile. h-k, Dicranum elongatum; Windermere, Zone 11; h, leaf : 13; j, apex of leaf (incomplete, but showing entire margin and cells) / 40; k, areolation, (i) apex, (ii) base (v = vein, m = margin). Zone II Rhacomitrium fasciculare is common in this zone. Polytrichum alpinum is very rare. Barbtda recurvirostra (Hedw.) Dix. (B. rubella Lindb.) Zone II This common moss was identified by Professor P. W. Richards from one specimen. Its habitat now is soil-capped rock ledges, etc. It is somewhat basicole, and more common in hilly districts. Pseudoleskea patens Limpr. Fig. i d-g. Zone II This is the most noteworthy of the species recorded, as it is only found, very rarely, on alpine rocks in the Scottish Highlands. It is readily identified, in the specimen, from the shape of the leaf, the areolation and the presence of a large papilla on the face of the cell on both back and front of the leaf. One specimen only was found.

3 30 W. PENNINGTON Dicranum elongatum Schleich. Fig. i h-k. Zone II This is another moss which is now rare and confined to Scottish mountains. I he straight slender stems interwoven with reddish tomentum, together with the leaf, which is smaller than that of D. fuscescens and almost entire, serve to identify the species. It is common at the base of zone II in one core from Low Wray Bay. Bryum cf. caespiticium is occasional. Hypnum spp., Hylocomium sp. and Bryum sp. are occasional. Zone III In Windermere, zone III is represented by a pink laminated clay containing no macroscopic organic remains. In a narrow band of grey clay at the base of the laminated clay, leaves oi Polytrichum alpinum were found. This is the only moss recorded from zone III. DISCUSSION The clay at the top of zone I in which Fontinalis squamosa occurs is apparently spread evenly over the lake fioor, and is of similar appearance in both deep water and the littoral regions. It would appear to have been deposited by inflowing streams entering the Lateglacial lake. The Fontinalis was probably growing in these streams as one of the first plants to colonize them after the rigours of the full-glacial period, and probably supported a rich epiphytic growth of the diatom Melosira arenaria. The detritus silt of zone II, on the other hand, shows strong local variations in its development, and appears to have accumulated from material washed into the margins of the lake, partly at least under conditions of solifluction. Even in the relatively mild period of zone II, the mean winter temperature yvould be much lower than today (Manley, 1959), and frost action would disturb the comparatively recent soils on the steeper slopes. The organic layer of zone II reaches its maximum development in sheltered bays, particularly at the foot of north- or north-east-facing slopes, as in Low Wray Bay, Windermere and Fold Yeat Bay, Esthwaite Water, and is completely absent in deep water. The organic silts of zone II therefore appear to incorporate remains of vegetation only from the slopes immediately surrounding each bay, with no contribution from the main inflow streams. Low Wray Bay receives drainage only from a very restricted area, so it can be assumed that the plants whose remains are found in its deposits of zone II were growing within a short distance of the lake shore. It can therefore be assumed that Pseudoleskea patens and Dicranum elongatum, two species now confined to alpine habitats, were present at about the altitude of Windermere at this time. The presence of Barbula rectirvirostra, suggests that this portion of the lake shore included habitats whose conditions are now found mainly on mountain rocks. The species of Hypnum, Hylocomium and Bryum recorded from this zone may well be those of rocky woodland, and the suggestion of the co-existence of these two habitats on the shores of Low Wray Bay during the milder chmate of zone II is supported by the remains of Betula species in the same deposit. Most of the abundant fruits and catkin-scales are clearly those of B. pubescens, indicating the presence of birch woodland, but the recent identification of B. nana and hybrids between it and the tree birches, from zone II in Windermere and Esthwaite Water, suggests that open habitats also existed round the lakes during zone II.

4 Late-glacial mosses 31 There is some evidence for regarding Pseudoleskea patens and Barbula recurvirostra as basicole species in this country (Dr. E. W. Jones, pers. comm.). Their presence in an area where the soils are now of low base status may be another indication of the general higher base status of the freshly exposed and unleached soils of the Late-glacial period. No mosses have been recorded from zone III except Polytrichum alpinum at the zone II/III boundary in Windermere, suggesting that conditions in Low Wray Bay were then in some respects similar to those which now obtain above 1500 feet. During the period of zone III, the corrie glaciation, there appears to have been very little incorporation of material from the surrounding slopes into the Windermere laminated clays. In Fold Yeat Bay, Esthwaite Water, where leaves of Salix herbacea are fairly frequent in the solifluction clay which is there the zone III deposit, it may be that further search would reveal moss remams. REFERENCES DixoN, H. N. (1924). The Student's Handbook of British Mosses. Sumfield, Eastbourne. ERANKS, J. W. & PENNINGTON, W. (1961). Late-glacial and Post-glacial deposits of the Esthwaite basin, N. Lancashire. Nezv PhytoL, 60, 27. GODWIN, H. (i960). Radiocarbon dating and Quaternary history in Britain. Proc. roy. Soc. B., 153, 287. MANLEY, G. (1959). Late-glacial climate of North-west ^England. Liv. and Man. Geol.J., 2, 188. PENNINGTON, W. (1943). Lake sediments. Nezv PhytoL, 42, i. PENNINGTON, W. (1947). Studies ofthe Post-glacial history of British vegetation. VHL Phil. Trans, rov. Soc. B., 233, 137. PENNINGTON, W. (1959). Relict fauna of Ennerdale Water. Nature, 184, ROUND, E. E. (1957). A note on some diatom communities in calcareous springs and streams. J. Linn. Soc. Bot., 55, 662. WATSON, E. V. (1955). British Mosses and Liverivorts. Cambridge University Press.

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