The relationships between modern pollen and floristic plant richness, diversity and evenness are assessed using pollen assemblages and associated vegetation data from 52 lakes along an elevational and vegetational gradient in the Setesdal valley of south-central Norway. Various data transformations were applied to minimise bias in the vegetation and pollen datasets. Plant species were transformed to their pollen or spore equivalents to reduce taxonomic biases. Pollen counts were transformed using Andersen’s general pollen-representation values for northern European trees and shrubs and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model with pollen-productivity estimates (PPEs) appropriate for Setesdal to minimise pollen-representation bias. Pollen count-size bias (before or after transformation) was eliminated by rarefaction analysis based on bootstrap resampling. Richness and diversity were quantified using Hill numbers ( N0, N1, N2), and evenness was estimated as the ratios of N0, N1 and N2. Diversity partitioning was used to estimate β diversity. The strongest correlations between pollen and plant richness and diversity are with pollen counts transformed using Andersen’s representation values and rarefied to a common count size and with plants transformed to their pollen equivalents. However, if sites from the low-alpine zone are excluded where there are high values of far-transported tree pollen, the richness and diversity relationships are also statistically significant for untransformed pollen data and plants transformed into their pollen equivalents. The effects of data transformation on diversity partitioning and estimates of β diversity are explored. We demonstrate that there are statistically significant positive relationships between pollen and plant richness and diversity along the entire elevational gradient after transforming the datasets to minimise biases due to taxonomic differences, differential pollen representation, and pollen-count size, and similar significant positive relationships along the forested parts of the gradient (nemoral, boreonemoral, southern boreal, middle boreal) after transforming the datasets to minimise biases due to taxonomic differences and pollen-count size.
Five collections of modern Picea glauca pollen, four of P. mariana, and two of P. rubens were examined in an attempt to distinguish the pollen of the species. Three morphological variables were recorded for individual grains in each collection. The sculpturing of the furrow membrane is not diagnostic, but the presence of an undulating margin to the cap and of irregular reticulation in the sacci characterize P. rubens pollen. Seven size variables were also measured for each grain. No simple combination of morphological and size criteria provides effective discrimination between P. glauca and P. mariana pollen.Linear discriminant analysis was applied to the size data for P. glauca and P. mariana. The mathematical assumptions of the method were tested, and to satisfy them, the discriminant analysis was confined to six of the seven variables measured. The discriminant analysis resulted in 91.5% of the pollen being correctly distinguished.The same six variables were measured on fossil Picea pollen from two Late Wisconsin sites in Minnesota and one Holocene sequence in Labrador. The individual fossil grains were assigned to either P. glauca or P. mariana by means of discriminant analysis. The Late Wisconsin spectra consist of both species, a result supported by macrofossil evidence. Picea glauca predominates in the early Holocene spectra from Labrador. It is replaced by P. mariana after about 5000 years before present, reflecting paludification and the spread of muskeg.The limitations of the procedure are discussed, and its potential is emphasized.
S ummary The lithostratigraphy of a section exposed at Sel Ayre on the Walls Peninsula, Shetland Mainland is described. A peat bed 50 cm thick is overlain by 7·3 m of sands, gravels, and boulder clay. Pollen analyses of this peat bed and of peat laminae in the sands reveal three distinctive pollen assemblages. These assemblages are interpreted as reflecting a vegetational development from grass‐ and fern‐dominated communities an fertile brawn‐earths to dwarf‐shrub heaths dominated by ericaceous shrubs including Bruckenthatia spiculifolia. These heaths grew on acid humus‐rich podsols and were replaced by open, grass‐dominated communities. Numerical comparisons of the Sel Ayre pollen spectra with pollen data from other sites on Shetland using principal components analysis suggest that three interglacial stages are represented on Shetland Mainland –Fiandrian, Ipswichian and Hoxnian. On the basis of the composition of the presumed long‐distance tree‐pollen rain, the Sel Ayre sequence is correlated with the Ipswichian stage. A basic interglacial cycle is proposed for the Shetlands.
S ummary A pollen diagram is presented from a 6 metre continuous core taken from Loch of Winless. Ten radiocarbon age determinations have been made from the sediments in relation to pollen stratigraphical changes and the sediments are found to cover the past 12800 years. On the basis of pollen stratigraphy the diagram is divided into five local pollen assemblage zones. Zones 1 and 2 may be correlated with the younger part of the Late Devensian ( sensu Mitchell et al. , 1973) whilst zones 3, 4 and 5 cover the Flandrian up to the present. The most notable aspect of the vegetational history of the area inferred from the fossil assemblages is the lack of tree‐cover at any time since the last glaciation. With the climatic amelioration at the beginning of the Flandrian period (approximately 10000 years B.P.), ‘dwarf‐shrub’ and ‘dwarf‐herb’ communities typical of the Late Devensian contracted and there was a widespread expansion of rich ‘tall‐herb’ and fern‐dominated communities with some small patches of willow and hazel scrub in sheltered sites. These in turn gave way to Calluna ‐dominated heaths on the well drained soils where podsolization and acidification were occurring.
Radiometric and AMS radiocarbon dating of a 6-m sediment core from Loch Ness, Scotland, indicates that it represents perhaps the very end of the Late Pleistocene, and the first ca. 7500 yr of the Holocene. Counts of laminations observed in the Holocene section of the core suggest that they are present in sufficient number to constitute annual laminations (varves), an hypothesis consistent with the pollen record, which contains a sequence of zones representative of the Early, Middle and part of the Late Holocene regional vegetation history. On the basis of BSEM and X-ray studies of sediments, and modern seston trap data, the laminations are believed to be produced by winter floods, which introduce increased silt loading into the Loch. Sediment for the rest of the year is mostly composed of clay-sized material. This hypothesis is being further tested, however, by continuing sedimentological and microfossil studies. Time-depth relations for the core based on calibrated 14 C dates and lamination counts, respectively, illustrate the close correspondence between the two sets of data. The latter are therefore now being used to develop a varve chronology for the Holocene for Loch Ness. This will then in turn be used for further chronological studies, and for investigations of palaeoclimatic variations over the eastern North Atlantic, to which the signal of lamination thickness in the sediments is thought to be particularly sensitive. They may also eventually be used for calibration studies, employing 14 C dating of specific carbon compounds, or groups of compounds extracted from the sediment using modern organic geochemical methods.
Investigations at Happisburgh, UK, have revealed the oldest known hominin footprint surface outside Africa at between ca. 1 million and 0.78 million years ago. The site has long been recognised for the preservation of sediments containing Early Pleistocene fauna and flora, but since 2005 has also yielded humanly made flint artefacts, extending the record of human occupation of northern Europe by at least 350,000 years. The sediments consist of sands, gravels and laminated silts laid down by a large river within the upper reaches of its estuary. In May 2013 extensive areas of the laminated sediments were exposed on the foreshore. On the surface of one of the laminated silt horizons a series of hollows was revealed in an area of ca. 12 m2. The surface was recorded using multi-image photogrammetry which showed that the hollows are distinctly elongated and the majority fall within the range of juvenile to adult hominin foot sizes. In many cases the arch and front/back of the foot can be identified and in one case the impression of toes can be seen. Using foot length to stature ratios, the hominins are estimated to have been between ca. 0.93 and 1.73 m in height, suggestive of a group of mixed ages. The orientation of the prints indicates movement in a southerly direction on mud-flats along the river edge. Early Pleistocene human fossils are extremely rare in Europe, with no evidence from the UK. The only known species in western Europe of a similar age is Homo antecessor, whose fossil remains have been found at Atapuerca, Spain. The foot sizes and estimated stature of the hominins from Happisburgh fall within the range derived from the fossil evidence of Homo antecessor.
Abstract Sedimentary pollen offers excellent opportunities to reconstruct vegetation changes over past millennia. Number of different pollen taxa or pollen richness is used to characterise past plant richness. To improve the interpretation of sedimentary pollen richness, it is essential to understand the relationship between pollen and plant richness in contemporary landscapes. This study presents a regional‐scale comparison of pollen and plant richness from northern Europe and evaluates the importance of environmental variables on pollen and plant richness. We use a pollen dataset of 511 lake‐surface pollen samples ranging through temperate, boreal and tundra biomes. To characterise plant diversity, we use a dataset formulated from the two largest plant atlases available in Europe. We compare pollen and plant richness estimates in different groups of taxa (wind‐pollinated vs. non‐wind‐pollinated, trees and shrubs vs. herbs and grasses) and test their relationships with climate and landscape variables. Pollen richness is significantly positively correlated with plant richness ( r = 0.53). The pollen plant richness correlation improves ( r = 0.63) when high pollen producers are downweighted prior to estimating richness minimising the influence of pollen production on the pollen richness estimate. This suggests that methods accommodating pollen‐production differences in richness estimates deserve further attention and should become more widely used in Quaternary pollen diversity studies. The highest correlations are found between pollen and plant richness of trees and shrubs ( r = 0.83) and of wind‐pollinated taxa ( r = 0.75) suggesting that these are the best measures of broad‐scale plant richness over several thousands of square kilometres. Mean annual temperature is the strongest predictor of both pollen and plant richness. Landscape openness is positively associated with pollen richness but not with plant richness. Pollen richness values from extremely open and/or cold areas where pollen production is low should be interpreted with caution because low local pollen production increases the proportion of extra‐regional pollen. Synthesis. Our results confirm that pollen data can provide insights into past plant richness changes in northern Europe, and with careful consideration of pollen‐production differences and spatial scale represented, pollen data make it possible to investigate vegetation diversity trends over long time‐scales and under changing climatic and habitat conditions.
Abstract Organic sediments in a gravel quarry at Block Fen, Cambridgeshire, form a sheet dividing lower from upper gravels. Analyses of pollen, macroscopic plant remains and molluscs from these organic sediments are presented. They indicate the presence of temperate freshwater and slightly brackish fine floodplain sediments, which, on the basis of the palaeobotany, are correlated with the temperate Ipswichian Stage. The freshwater sediments, ascribed to Ipswichian substage IIb, occur at ca. −3 m OD. Marine‐influenced tidal sediments, ascribed to Ipswichian substage III, occur at ca. −6 m OD. No evidence was found for the presence of more than one temperate stage in the sequence. The lower gravels are then correlated with the cold Wolstonian Stage and the upper gravels with the cold Devensian Stage. In contrast to the woodland environments indicated by the palaeobotany of the Ipswichian organic sediments, post‐Ipswichian pollen diagrams and macroscopic plant remains in the upper suite of sands and gravels indicate open tree‐less vegetation typical of the cold Devensian Stage. They also contain a typical cold‐stage mollusc fauna. The sediments containing these floras and faunas are associated with thermal contraction cracks, indicating the presence of permafrost. The final sand and gravel aggradation in the Devensian forms the Block Fen Terrace, near 0 m OD. The evidence indicates that it is younger than the lacustrine sediments resulting from the blocking of the Fenland at the Wash by Late Devensian ice at ca. 18.5 ka BP. The sequence at Block Fen is related to nearby Ipswichian and Devensian sediments at Chatteris, March, Wimblington and Mepal, and to deposits at Wretton on the east margin of Fenland. The correlation permits an outline reconstruction of the history of the valley carrying the River Great Ouse between the Isle of Ely and the Chatteris and March ‘islands’ from the time of a gravel aggradation before the Ipswichian to the Flandrian. The reconstruction shows the time and level of the Ipswichian marine incursion into the Middle Level of Fenland and the extent of aggradation and erosion in the Devensian.
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