Liderazgo situacional

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Release of pollen

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Preparation of sample

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Sample count

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Interpretation

Fig«le3 The preparation and interpretation of pollen assemblages (Crabtree 1975)

sediments also'allows investigation of the differential preservation of pollen within them. Differential preservation is mainly a feature of soils and deposits which are either aerobic, biologically active or rather alkaline but some degree of pollen deterioration is found in all deposits and general counts of deteriorated pollen have been used as evidence of changes in the character of sediment accumulation.

The organisation of the thesis falls into three parts. The first part, comprising Chapters 1 and 2 is introductory, the second Chapter presenting the background to the development of pollen analysis in Scotland and detailing the general picture of vegetation history over the last 14000 years in Scotland. In the second part, Chapter 3, the details of the surface pollen work undertaken on Bankhead Moss in Fife are presented and the main results summarised. The third part, Chapters 4 to 9 which provides the main body of the work, covers the results from the three environments within the study area. Chapter 4 discusses the background characteristics of the area, its geology, soils, climate, archaeological and historical records. Chapter 5 presents the results from cores taken from the margins of Stormont Loch in Strathmore and shows the pattern of vegetation change on lower ground throughout the Late Devensian and Flandrian periods. Chapter 6 discusses results from two peat sites and three soil pollen sites on the higher plateau of the Forest of Alyth north of the Highland Boundary Fault which together cover all the Flandrian, and Chapter 7 deals with the results from a short core taken from Loch Mharaich, the highest site analysed, on the Strathardle-Glenshee watershed. In Chapter 8 the results from analyses carried out at two archaeological sites at Moncreiffe House in southern Perthshire and Queen’s View in western Perthshire are considered and related to the results from the eastern area. Finally in Chapter 9 the patterns of vegetation change during the Late Devensian and Early

and Middle Flandrian. are discussed in terms of regional pollen assemblage zones, and the effects of man on the vegetation of the area during the later Flandrian are summarised.

AO

CHAPTER TUP

VEGETATIONAL HISTORY OF SCOTLAND

i) The development of pollen analysis in Scotland

The development of pollen analysis in Scotland has been the subject of a paper by Edwards (1974) in which, with the aid of a

comprehensive bibliography, he discusses the progress of pollen analysis since the publication of the first Scottish pollen diagrams by Erdtman in 1923. Prior to the work of Erdtman, studies of past vegetation patterns were based on the analysis of peat macrofossils. Geikie

(1866, 1894) and Lewis (1905, 1906, 1907, 1911) both studied peat deposits throughout Scotland and related changes in peat composition to climatic oscillations suggesting a system of alternating warm and cool periods. Samuelson (1910) also examined many Scottish peat deposits, especially those visited by Lewis, and he attempted to cor­ relate the Scottish chronology with that of Scandinavia as outlined by Blytt and Sernander. Erdtman (1923, 1924, 1928) was also interested in establishing common ground between the climatic development of

nothern Britain and Scandinavia and by means of the identification of the pollen of several arboreal species he was able to determine the sequence of the immigration of trees into Scotland following the last glaciation.

It was not until the Second World War that Fraser (1943) and later Fraser and Godwin (1955) published pollen diagrams for Aberdeenshire and Lanarkshire which seemed to show a development of vegetation similar to that already demonstrated by Godwin in southern Britain (1940).

The history of woodland throughout Scotland since Boreal times was the subject of a doctoral thesis by Durno (1967) in which he analysed over fifty sites throughout the country, using widely sampled,

generalised diagrams. In his study, Durno succeeded in establishing regions of different forest composition, showing birch to be found consistently all over Scotland throughout the Flandrian, albeit secondary to pine in the north and to oak in the south, Durno’s diagrams and those of Newey (1967) from southeast Scotland continued to use the Godwinian system of zonation. Doubts concerning the value of this method of zonation for use in Scotland had been raised as early as 1946 by Blackburn who discovered that from an island site, in this case Barra, non-arboreal pollen rather than arboreal pollen was the dominant feature of the pollen diagrams. These findings were confirmed on Canna by Flenley and Pearson (1967), on Orkney by Moar (1969a) and on Shetland by Hawksworth (1969). On the mainland, both Vasari and

Vasari (1968) and Donner (1962) used Godwinian zones but expressed doubts over their utility, Donner especially having difficulty in defining any boundaries between zones V and VI, and between VIIb and VIII. Pears (1969), in the light of his investigation into the former altitudinal variations of pine in the Cairngorms, ekpressed further

concern; _ '

”It could be that it is a serious mistake to try to fit Highland pollen diagram zonation too closely into the well established lowland sequence.’' (Pears, 1969, p.541)

Studies in the Orkneys, Sutherland and southwest Scotland by Moar (1969a, 1969b, 1969c) and in the Cairngorms, Ross and Cromarty and Galloway by H.H. Birks (1970, 1972a, 1972b) abandoned the use of Godwinian zones. Floar developed a system of biostratigraphic zones, based entirely on pollen content, zones which, especially during the Devensian, were independent both of lithostratigraphy and established pollen sequences. H.H. Birks (1970) introduced into Scotland the idea of the pollen assemblage zone as outlined in the American Code of

Stratigraphic Nomenclature (American Commission, 1961),

”An assemblage zone is defined on the presence and relative proportions of the contained fossils, and named after the most abundant and characteristic taxa. It is independent of any ecological, chronological or climatic interpretations*1’

Using this method, local assemblage zones for a particular site and regional assemblage zones based on information from several sites within a region may be determined* Such regional assemblage zones may be further refined by radiocarbon-dating their boundaries to produce chronozones* So far, only sites in northern Scotland and southeast Scotland have been subjected to such analysis (Pennington et al., 1972 Pennington, 1975a; Switsur and West, 1976), The work of Pennington et al. (1972) and Pennington and Lishman (1971) also remains as the only use of the analysis of sediment chemistry as an adjunct to pollen analysis in Scotland, except for work on Skye for the Late Devensian period by H.3.8. Birks (1973a), and in Aberdeenshire where Edwards

(1977, 1979) has also included evidence of the magnetic properties of

sediments. _

The problems of regional disparity in vegetation development and the non-synchroneity of apparently similar events in the pollen record are very apparent from many Scottish pollen diagrams. Recently,

however, there has been a spatial bias in the analysis of sites, which has left certain areas better understood than others. Interest has centred on areas of relict oakwood in the northwest and southwest (H.H. Birks, 1972a, 1972b) and in areas of relict pinewood, the

remnants of the Caledonian pine forest (H.H. Birks, 1970; Pennington et al., 1972; O’Sullivan, 1974a, 1975). Large areas of eastern and central Scotland have yet to be covered by any detailed studies although the foundations for such studies have already been laid by

Durno (1956, 1959) and Donner (1952). ,

Despite the patchy nature of our knowledge with regard to the Flandrian there has been considerable interest in Scottish Late Devensian environments culminating in the recent work edited by Gray and Lowe (1977). Following early work by Mitchell in Berwickshire and near Glasgow (1948, 1952), Donner (1957, 1958) investigated several Late Devensian profiles and considered their relationship to supposed Zone III, Loch Lomond Stadial, limits. This theme has since been expanded, especially in the southeast Grampians, under the influence of Sissons (Sissons and Walker, 1974; Walker, 1975a, 1975b; Lowe and Walker, 1977) so that a clearer picture of vegetation changes associated with the oscillations of the last ice caps is now emerging. Pennington et al. (1972) concentrated on the Late Devensian in northwest Scotland and in several papers Pennington (1973, 1975a, 1975b, 1977b) has

investigated this period by the use of absolute pollen techniques, the first person to publish diagrams using this more refined counting technique in Scotland. Further information on the Late Devensian in northwest Scotland has been ascertained from Skye by K.3.B. Birks (1973a) who used an analysis of the present flora and its characteristic pollen spectra to aid the interpretation of former vegetation assemblages. Inextricably linked with the extent and effects of the last glaciation is the question of sea level changes, a subject reviewed by Donner

(1970). One benefit for the interpretation of Flandrian environments to emerge from work in this area has been the analysis of peats below the Carse clay of the Forth valley, (Newey, 1966; Brooks, 1972), analyses carried out ostensibly to help date the onset of the major Flandrian marine transgression.

Interest in Scotland in the Late Flandrian period and in the anthropogenic factor in vegetation history has been limited. Indeed

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it would be fair to say that in many areas vegetation changes .

. $ associated with the final stages of the last glaciation, over 10000

years ago, are better understood than those associated with the human activity of the last 5000 years. Except for a brief paper by Knox (1954) and the recognition of human influences in rather generalised pollen diagrams for Perthshire and Ayrshire by Durno (1965), only Nichols (1967) and Turner (1965, 1970, 1975) have consciously

•'& investigated the effects of early man on his environment. It is true

that many others, such as Donner (1962) and Moar (1969b), have observed

what they assumed to be anthropogenic interference with the vegetation ■ > .'5^. cover, but their sampling interval was too great to note the precise _t.C; changes taking place and the interpretation of such phenomena was not

?5

the main object of their work. H.H. Birks (1972a) only found it

possible at one site, Snibe Bog in Galloway, to establish a pattern 5• of human clearances, based on a varying sample interval of 5 cm and ■ J T1" 10 cm. By selective close sampling of profiles from Aros Moss in

Kintyre and Racks Moss in Dumfries Nichols (1967) was able to demon- strate probable Mesolithic and definite Neolithic and later inter- ference with the forest cover in the form of several small scale

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• clearances for both pastoral and arable agriculture. Turner (1965),

'fi

clearances from the post-Neolithic period at Bloak Moss in Ayrshire $

and Flanders Moss in Perthshire. In Ayrshire, she was able to dif-

"it

St ferentiate between ’small temporary clearances’ and ’extensive

clearances’, and attempted to locate the areas in which clearance A

was taking place. The absence of studies of the effects of man on the prehistoric landscape in the east of Scotland is perhaps surprising

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