This thesis describes the results of pollen analysis and radiocarbon
dating of mainly basal sediments from enclosed presently peat-filled
hollows in southern Perthshire, and the environmental implications of
the results are discussed with special emphasis on the glacial sequence
and the development of vegetation and soils during the Lateglacial and
early Flandrian in southern Perthshire. The pollen diagrams presented
are all based on relative pollen percentages, and in interpreting such
diagrams two approaches are considered to be fundamental. Firstly, a
number of major problems that affect the interpretation of pollen
assemblages in general but Lateglacial assemblages in particular are
discussed in detail prior to the correlation and interpretation of the
local pollen zones. Secondly, since for a variety of reasons the
regional importance of particular taxa may be strongly misrepresented
in any individual pollen diagram, interpretations of the local pollen
zones are to a large extent influenced by the results of similar
investigations for other parts of the country. Thus reviews of and
comparisons with data from other parts of Scotland (and selectively from
the British Isles as a whole) form an important part of this thesis. In
addition, useful indications of palaeoenvironmental changes have resulted
from the analysis of deteriorated pollen grains. This aspect of pollen
analysis is usually ignored in routine pollen counting. The causes of
the different kinds of deterioration as well as interpretations of their
varying frequency are discussed in some detail.
Evidence from the Lateglacial deposits in southern Perthshire
suggests that plant colonisation commenced shortly after 13,000 B.P. and
that deglaciation was widespread by that time. Plant successions
followed an uninterrupted sequence between about 13,000 and 11,000 B.P.
(the Lateglacial Interstadial) from the predominantly open-habitat taxa
of the colonisation period, to the closed grasslands with juniper, willow and copses of tree birch that characterised the lower-lying areas
towards the end of the Interstadial. Moss heaths and poor grassland
communities characterised the higher slopes. After 11,000 B.P. climatic
conditions became much harsher, resulting in the Loch Lomond Readvance
of glaciers, the break-up of existing soils, and revertence to openhabitat
plant communities throughout southern Perthshire during the Loch
Lomond Stadial (11 ,000 - 10,000 B.P.). A number of valley glaciers
existed in southern Perthshire at this time, with the lowest and most
southerly glacier terminus in this region near Callander. Rapid climatic
amelioration shortly before 10,000 B.P. resulted in the cessation of
solifluction processes, and a plant succession was then initiated that
led to the immigration of birch woodland into parts of this area by
about 9,500 B.P.
During the Flandrian a basically similar vegetational history is
recorded at each site, with the following main phases: the expansion
of juniper, the immigration and expansion of birch woodland, the
development of a dominant birch-hazel woodland, and the decline of hazel
following the immigration of elm and oak. At three sites the main Alnus
rise is recognised, and the Elm Decline is positively identified at only
one site. The climax forest of lowland Perthshire was a mixed oak-elmbirch
association probably associated with brown forest soils. On
upland sites woodlands were much lighter with birch the most important
tree, the climax forest varying between birch-alder-hazel and birchalder-
pine, with oak invading some of the higher valleys. At about
6,500 B.P. marked changes in mire stratigraphy, pollen assemblages and
amounts and type of deteriorated pollen are recorded, probably related
to a major transition from a relatively dry climate to a climate with
markedly oceanic characteristics.
The Lateglacial and early Flandrian radiocarbon dates from sites
in southern Perthshire are compared with other available dates from
Scotland and the chronology and terminology of the Lateglacial are
discussed. It is concluded that chronostratigraphic boundaries are
at present poorly defined and that boundaries proposed in recent schemes
may bear little relationship to times of major climatic change in
Scotland. The thesis concludes by stressing the need for more detailed
analyses for sites in southern Perthshire, employing absolute pollen
counts, the analysis of deteriorated pollen and spores, and analysis of
coleopteran remains in Lateglacial and early Flandrian sediments.
