Results from the palaeoenvironmental investigations into the Holocene vegetation history of three sites in eastern lowland Scotland are presented. Two of the sites, Cruvie and Pitbladdo, are located in north Fife; the third site, Methvern is situated in south Perthshire. Cruvie is located in a kettle-hole and provides data extending from the Late-glacial to ea. 3900 BP. Pitbladdo is a former bog and cores from this site provide data on the period from ca. 8000 to 3900 BP. Methvern is a well-maintained raised bog and provides data that spans the entire Holocene. Relative, concentration and pollen preservation data are supplemented by loss-on-ignition, pH and magnetic susceptibility analyses. Microscopic charcoal data are also recorded. Radiocarbon dates allow comparisons to be made between similar events at different sites, resulting in a detailed picture of temporal and spatial patterns of palaeoecological change within a small geographical area. Attention is focused upon the identification of human impact on the environment during the early to mid Holocene. The influences of succession and climate change in determining patterns of vegetation change are also considered. The data obtained indicate that human activity may have had a limited impact on the environment in this area during the Mesolithic, but no unequivocal evidence is recorded. Anthropogenic impacts are more clearly identified during the Neolithic period and from the late Neolithic/early Bronze Age, human activity is considerable and includes pastoral and mixed farming. The value of tephra as a dating tool in this area of eastern Scotland is considered. The absence of tephra at the three sites investigated has led to the formulation of a hypothesis linking patterns of orographic rainfall and tephra deposition within Scotland. The study highlights the difficulties of determining the causal factors of vegetation change and the limitations of palaeoecological data in the identification of anthropogenic activity during the early Holocene. The recognition of climate signals is discussed and the routine counting of microscopic charcoal at all sites is proposed. It is suggested that further research is required to clarify the boundaries of tephra deposition in Britain. Finally the diverse patterns of change recorded within the study area emphasise the need for a network of closely spaced and well dated palaeoenvironmental sites covering the regions of Scotland, leading to the recognition of local patterns of environmental change.

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The southwest monsoon is responsible for a summer precipitation maximum for much of the southwest U.S. Biostratigraphies of pollen, plant macrofossils, and aquatic fossils in lakes from near modern monsoon boundaries in conjunction with climate modelling suggests variations in strength of the monsoon system during the late Quaternary. At Montezuma Well, Arizona, high percentages of Pinus and Juniperus pollen as well as maximum influxes of Quercus and Gramineae pollen suggest a shift from dominantly winter to summer precipitation between ca. 12,000 and 9000 yr BP. Maximum aridity occurred 7000-4000 yr BP, coincident with lowest lake levels. In the High Plateaus region of the Colorado Plateau, high Artemisia to Chenopodiaceae-Amaranthus pollen ratios suggests precipitation maxima until ca. 6000 yr BP at Fryingpan Lake and 5000 yr BP at Posy Lake. Pollen records suggest that Pinus edulis, P. ponderosa, and Quercus gambelii, were present on the western Colorado Plateau throughout the Holocene. Expansion of shadscale steppe vegetation at low elevations and upslope movement of ecotones for Pinus edulis, P. ponderosa, and Q. gambelii after ca. 6000 yr BP and low lake levels ca. 5000-3700 yr BP, suggest a period of maximum aridity from decreased summer precipitation. In the San Luis Valley, Colorado, pollen records from Head Lake on the basin floor suggest an expansion of oaks and junipers at the Pleistocene/Holocene boundary that may indicate increased summer precipitation. Lake levels of Head Lake fell sharply after ca. 9500 yr BP. Pollen records from Como Lake in the Sangre de Cristo Mountains suggest that Pinus ponderosa was established in the area by ca. 12,000 yr BP and Pinus edulis by ca. 9500 yr BP. Highland regions such as the High Plateaus (until ca. 6000-5000 yr BP) and central Colorado (until ca. 4000 yr BP) may have experienced Holocene summer precipitation maxima later into the Holocene than sites in lower elevation regions. Regional orographic uplift as a catalyst for convective summer precipitation may be responsible for the duration of summer precipitation maxima in these regions. On a longitudinal gradient, sites to the west such as in the southern Great Basin and Mohave Desert may have recorded enhanced summer precipitation earlier, reflecting different histories of the low-level jets in the southwest. The paleoecologic record generally confirm predictions of general circulation models (GCMs) that southwest monsoon circulation was enhanced from 12,000-6000 yr BP in response to peaks in annual (11,500-11,000 yr BP) and summer insolation (10,000-9000 yr BP) during the late Quaternary.

Palaeobotanical records of Holocene climate change in the southern Coast Mountains identify a cooler/wetter Neoglacial period subsequent to 6600 BP. Geomorphic evidence of alpine glacier advance suggests that there were three distinct cooler/wetter periods during the Neoglacial, but this pattern has not been identified in palaeobotanical studies. By careful selection of a sensitive alpine site this thesis has recognised this structure in a palynological record of Neoglacial climate. This continuous record of Neoglacial climate which has the same basis as records of early Holocene climate (i.e. palynological) and hence allows more direct comparisons of the two periods. Pollen spectra, conifer needle macrofossils, organic matter content, and magnetic susceptibility were assessed for a 4800 year continuous sequence of sediment from an alpine lake. Calibration of the Picea/Pinus pollen ratio by using an altitudinal transect of surface pollen samples allowed partial quantification of shifts in treeline. Treeline at the site was at least 85 m above the present level from 4800-3800 BP, suggesting that summer temperatures were at least 0.6°C above the present. High treeline until 3800 BP indicates a relatively late date for the Hypsithermal/Neoglacial transition at this site. Alternatively, the apparent complexity of this transition in the Coast Mountains may be due to difficulties of separating temperature and precipitation signals in many climatic records. Treeline declined to near present levels by 2500 BP and was lower than present from 2500-1500 BP and from 1200 BP until close to the present. Estimates of equilibrium line altitude depression for Coast Mountain glaciers during the Little Ice Age suggest that these periods of lower treeline were due to a cooling of up to 0.8°C. During the last 5000 years the Southern Coast Mountains have experienced fluctuations on the order of 1.5°C.

Palaeobotanical records of Holocene climate change in the southern Coast Mountains identify a cooler/wetter Neoglacial period subsequent to 6600 BP. Geomorphic evidence of alpine glacier advance suggests that there were three distinct cooler/wetter periods during the Neoglacial, but this pattern has not been identified in palaeobotanical studies. By careful selection of a sensitive alpine site this thesis has recognised this structure in a palynological record of Neoglacial climate. This continuous record of Neoglacial climate which has the same basis as records of early Holocene climate (i.e. palynological) and hence allows more direct comparisons of the two periods. Pollen spectra, conifer needle macrofossils, organic matter content, and magnetic susceptibility were assessed for a 4800 year continuous sequence of sediment from an alpine lake. Calibration of the Picea/Pinus pollen ratio by using an altitudinal transect of surface pollen samples allowed partial quantification of shifts in treeline. Treeline at the site was at least 85 m above the present level from 4800-3800 BP, suggesting that summer temperatures were at least 0.6°C above the present. High treeline until 3800 BP indicates a relatively late date for the Hypsithermal/Neoglacial transition at this site. Alternatively, the apparent complexity of this transition in the Coast Mountains may be due to difficulties of separating temperature and precipitation signals in many climatic records. Treeline declined to near present levels by 2500 BP and was lower than present from 2500-1500 BP and from 1200 BP until close to the present. Estimates of equilibrium line altitude depression for Coast Mountain glaciers during the Little Ice Age suggest that these periods of lower treeline were due to a cooling of up to 0.8°C. During the last 5000 years the Southern Coast Mountains have experienced fluctuations on the order of 1.5°C. / Arts, Faculty of / Geography, Department of / Graduate

The past stability of vegetation patterns in the Markham Valley (6°30’S, 146°30’E), a lowland grassland area of Papua New Guinea, is investigated by pollen analysis of lake deposits and related palaeoecological techniques.¶ The predominantly organic sediments of Lake Wanum (alt. 35 m) span the last 9600 years. A 14C chronology supports the calculation of annual pollen deposition, sediment accumulation, and carbonised particle influx rates. At Yanamugi lake (alt. 170 m), 14C assays of the calcareous muds are influenced by variable ‘hard- water error’. A tentative chronology is based on palaeomagnetic and tephra correlations.¶ Pollen trapping reveals very high contemporary annual deposition rates within forest, but low values over the central lake area. Surface pollen assemblages from different habitats indicate the localised nature of pollen dispersal, although a relatively ‘long-distance component’ from higher altitudes is also recognised.¶ Analysis of floristic data from the herbaceous swamp vegetation of Lake Wanum suggests the existence of two free floating root-mat associations and two or three rooted associations. Water depth appears the primary control on their distribution.¶ Holocene swamp communities analogous with extant associations may be identified in the palynological record of Lake Wanum. Swamp marginal conditions prevail from 9500 BP until 8200 BP when permanent shallow water becomes established. Rooted vegetation associations then predominate until about 5000 BP. Floating vegetation associations first become important at this time, and subsequently (3000 BP to 2000 BP) come to dominate the site. A general trend towards increased water depth is indicated throughout the sequence.¶ Increased representation of dry-land non-forest pollen occurs from 8550 BP, and grassland taxa become more frequent from about 5350 BP. Synchronous trends in carbonised particle influx identify fire as a probable agent of vegetation change.¶ Little change in dry-land vegetation is recorded in the pollen sequence from Yanamugi, although recent encroachment by swamp vegetation occurs. The large proportion of ‘montane’ pollen and spore taxa in the earlier sediments is attributed to variable fluvial influx. ¶ Conditions at Lake Wanum until 8200 BP may reflect the early Holocene aridity widespread in equatorial areas, although the indirect hydrologic effects of rising sea level cannot be discounted. Human impact appears the main determinant of dry-land vegetation change during much of the Holocene.