The Holocene history of Pinus sylvestris woodland in the Mar Lodge Estate, Cairngorms, Eastern Scotland

Abstract

Abstract This thesis investigates the past extent, structure and dynamics of Mar Lodge Caledonian pine (Pinus sylvestris L.) woodland, near Braemar in the south-eastern Cairngorms. The geographical extent and Holocene history of the Scottish pinewoods are generally understood, but the Mar pinewoods are relatively obscure. This thesis is concerned with the Holocene history of the Mar pinewoods; the timing and reasons for first appearance, the increase in abundance of Pinus to become a dominant species, the spatial extent of the woodland and its structure and form. The investigation includes changes to the woodland assemblage during its fragmentation and disappearance in the late Holocene and possible influences on the woodland from people living in the area. At the heart of this thesis is an understanding of the factors underpinning the ecology of Pinus and the response of the species to competition with other taxa. This is related to the spatial and temporal changes in climate that contribute to the location and development of Pinus in Scotland and Mar Lodge. Areas comparable to Mar Lodge are defined as ‘core areas’ of pine woodland rather than ‘native areas’. This avoids the necessity of considering every short period of colonisation by Pinus in areas distal to large populations. The location, extent, form and behaviour of woodland according to macro sub-fossils and micro sub-fossils is used to define core woodland as those with a long presence of Pinus, often continuing to the present day. Areas with a long history but no extant population are regarded as peripheral areas. This thesis consists of extensive palaeoecological investigations of three peat sequences: from within extant pine woodland (Doire Bhraghad), from just beyond its edge (White Bridge) and from peat with sub-fossil pine stumps located 10km west of the modern range of Pinus (Geldie Lodge). A range of techniques, including loss of mass on ignition and colorimetric light transmission analysis are applied to the peat, but palynological techniques form the basis of the investigation. Stomatal counts are used in conjunction with pollen counts to explore the process of Pinus colonisation, and its increase in abundance to form woodland. Pinus percentage and influx, together with the ratio of arboreal to non-arboreal pollen and the percentage of Empetrum are used to define the density of the woodland canopy. The stability of the Doire Bhraghad assemblage confirms the area as core Pinus woodland. Pinus is present from c. 9600 cal BP and dominates woodland from c. 9150 cal BP. Woodland here is a closed, solely Pinus canopy from c. 8600 until 4000 cal BP. Arrival of Pinus at Geldie Lodge is undated but occurs before c. 7550 cal BP. Woodland is always more open; Pinus is co-dominant with Betula, showing affinity with other peripheral areas. Pinus woodland fragments at all Mar Lodge sites from c. 3900 cal BP, disappearing from Geldie Lodge by c. 2800 cal BP and White Bridge by c. 1900 cal BP. Calluna replaces Pinus as the dominant species at all three sites. The disappearance of Pinus is thought to relate to regional climatic change toward wetter conditions. At Geldie Lodge a prior Coleopteran study suggests Pinus growing on the mire surface to be small and short lived. These may not have been the only trees growing in the area but they perhaps contributed to the major fluctuations in arboreal and non-arboreal pollen. Early canopy fluctuations (c. 7550 to 6000 cal BP) at Geldie Lodge may be related to Mesolithic human activity; there is stronger evidence of human presence from c. 4000 cal BP, possibly including cereal cultivation. Evidence from Doire Bhraghad and White Bridge is indicative only of low intensity grazing activity. It is unlikely that human activity instigated the fragmentation and disappearance of woodland, but may have contributed to the process.