Hilary H. Birks

The cultural landscape - past, present and future.

Cambridge University Press. Paperback. Book Condition: New. Paperback. 540 pages. Dimensions: 9.6in. x 7.3in. x 1.2in.The Cultural Landscape Past, Present and Future considers different aspects of mans intervention with natural vegetation and the landscape resulting from a long equilibrium of co-existence. These landscapes are not stable, and the recent and ever accelerating changes in technology and life-style have increasingly affected many ancient landscapes, as old land-use practices are abandoned and traditions forgotten. The papers in this book describe and...

The development of the aquatic ecosystem at Kråkenes Lake, western Norway, during the late glacial and early Holocene - a synthesis

This paper synthesises the palaeoecological reconstructions, including palaeoclimatic inferences, based on the available fossil record of plants (pollen, macrofossils, mosses, diatoms) and animals (chironomids, Cladocera, Coleoptera, Trichoptera, oribatid mites) in the late-glacial and early-Holocene sediments of Kråkenes Lake, western Norway, with special emphasis on changes in the aquatic ecosystem. New percentage and influx pollen diagrams for selected taxa provide insights into the terrestrial setting. The information from all the proxies is collated in a stratigraphical chart, and the inferred changes in the lake and its catchment are discussed. The individual fossil sequences are summarised by detrended correspondence analysis (DCA), and sample scores on the first DCA axes are plotted against an estimated calendar-year timescale for comparison of the timing and magnitude of changes in assemblage composition. The DCA plots show that the large late-glacial biotic changes were synchronous, and were driven by the overriding forcing factor of temperature. During the early Holocene, however, the changes in different groups were more gradual and were independent of each other, showing that other factors were important and interactive, such as the inwash of dissolved and particulate material from the catchment, the base and nutrient status of the lake-water, and the internal processes of ecosystem succession and sediment accumulation. This multi-disciplinary study, with proxies for changes in the lake and in the catchment, highlights the dependence of lake biota and processes not only on regional climatic changes but also on changes in the lake catchment and on internal processes within the lake. Rates of change for each group are also estimated and compared. The reaction times to the sharp temperature changes at the start and end of the Younger Dryas were very rapid and occurred within a decade of the temperature change. Aquatic organisms tracked the temperature and environmental changes very closely, and are probably the best recorders of late-glacial climatic change in the fossil record.

Changes in North Atlantic Radiocarbon Reservoir Ages During the Allerød and Younger Dryas

Estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late Quaternary climate. We radiocarbon-dated marine shells and terrestrial plant remains deposited in two bays on Norways west coast between 11,000 and 14,000 years ago, a time of large and abrupt climatic changes that included the Younger Dryas (YD) cold episode. The radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early YD, stabilized for 900 years, and dropped by 300 years within a century across the YD-Holocene transition.

Species-environmental relationships of aquatic macrophytes in Northern Ireland

Abstract A data-set from 574 lakes in Northern Ireland was used to analyse the individual relationships of the occurrence of aquatic macrophytes to the lake environment. The 32 most frequent species were used in the analyses. The 21 environmental parameters recorded for each lake were divided into five groups; (1) geographical features; (2) lake physical variables; (3) lake-water chemistry summary variables; (4) lake-water major ions; and (5) lake-water nutrients. The species–environmental relationships were analysed using generalised additive models (GAM) and canonical correspondence analysis (CCA). The results were interpreted in terms of expected range, tolerance, and optimum of each species. Predictive models were made for each of the most frequent aquatic macrophytes along individual environmental gradients. The most influential variables are related to local-scale chemical and nutrient composition, both of which are highly correlated with altitude because hardwater, nutrient-rich lakes are restricted to the lowlands. Major ions and nutrients constrain the species into two groups associated with either low or high ionic concentration. The high ionic concentration group of species may be further divided into those associated with calcareous lakes or lakes with high sodium and chloride. Local-scale variation in lake chemistry and the strong environmental responses of the aquatic macrophytes suggest a strong local influence on species composition of different lakes, leading to the interpretation that the occurrence of a species in a lake is predominantly controlled by the catchment use, particularly farming and fertiliser use.

A calendar age estimate of the Younger Dryas-Holocene boundary at Kråkenes, western Norway

The Younger Dryas/Holocene transition (YD/H) in the sediments of Kråkenes Lake, western Nor way, is well marked both lithologically and palaeobiologically at 756.5 cm in the investigated core. A series of 70 AMS radiocarbon dates on terrestrial plant macrofossils and the NaOH-soluble fraction of lake sediment was measured between 585 and 840 cm, covering the time span c. 10 440 to 7915 BP on the radiocarbon timescale. Forty-three of these dates above 760 cm were wiggle-matched against the German oak-pine dendro calibration curve (IntCal 93) with recent corrections in both the oak and the pine sections. With an increase in age of the pine dendro-series of 200 6 20 yr, the calendar age of the YD/H lithostratigraphic boundary at Kråkenes is estimated to 11 530+40 -60 cal. BP. By using a date of 9750 BP (11 170 cal. BP) on the transition between the 10 000 and 9600 14C plateaux as a time marker, this result is compared with recent results from other archives. It is consistent with many of them, including the GRIP ice core, German pine series, Lake Gościaz, south Swedish lakes, and Baltic varves, suggesting that the Younger Dryas-Holocene transition in the North Atlantic region occurred within the range 11 500–11 600 cal. BP.

Holocene vegetational history and climatic change in west Spitsbergen - plant macrofossils from Skardtjørna, an Arctic lake

Macrofossil analyses of a 335 cm-long core from Skardtjørna, a small lake on the west coast of Spitsbergen, Svalbard, are presented. The known processes of deposition of plant remains to arctic lake sediments are summarised, and used in the interpretation of the vegetation history at Skardtjørna. The basal sediment is AMS-dated to 8110 ± 110 BP. The rest of the profile is dated by palaeomagnetic correlation. The lowest sediments have the greatest macrofossil concentration and numbers of taxa per sample. The occurrences of Cassiope hypnoides and Salix cf. glauca before 4000 BP indicate a mean July temperature for the early Holocene about 2°C higher than today, comparable to the Cassiope tetragona vegetation zone of the mid-arctic region of the inner fjords. Increasing climatic severity resulted in the threshold from the Cassiope to the Dryas vegetation zone being passed at about 2500 BP. The inferred climatic history at Skardtjørna is compatible with other evidence from Svalbard and elsewhere in the arctic. The phytogeography of Salix herbacea, Cassiope hypnoides, and Saxifraga flagellaris is discussed in terms of their historical occurrences.

Biological responses to rapid climate change at the Younger Dryas-Holocene transition at Krakenes, western Norway

A fine-resolution pollen-stratigraphical study, supported by macrofossil analysis, has been made at Kråkenes Lake, western Norway through the Younger Dryas—Holocene transition and the early Holocene. The median sample-age difference is 14 cal. yr for the period 9175—11625 cal. yr BP. The chronology is based on 57 AMS radiocarbon dates. The pollen stratigraphy is interpreted as a primary succession following deglaciation at the end of the Younger Dryas. Palynological richness, compositional turnover and rates of assemblage change are estimated from the pollen-stratigraphical data. Comparisons between palynological turnover at Kråkenes and floristic turnover on recently deglaciated modern glacier forelands suggest a comparable primary succession and turnover at Kråkenes. However, the arrival and expansion of Betula pubescens (tree birch) was delayed by about 450 years. Possible reasons for this lag are discussed. Comparisons between turnover estimates for pollen and for diatoms through the Younger Dryas—Holocene transition highlight differences in the response dynamics of terrestrial and aquatic ecosystems at Kråkenes Lake. This fine-resolution study links the long temporal perspective provided by palaeoecology with the fine temporal scales of modern ecological observations. The primary succession following rapid climate warming at Kråkenes provides a context for other past and present responses to climate warming and it can provide a long-term perspective on responses to projected future climate warming.

Looking forward through the past : identification of 50 priority research questions in palaeoecology

Summary 1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on timescales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. This article is protected by copyright. All rights reserved. Accepted Article 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human–environment interactions in the Anthropocene; biodiversity, conservation, and novel ecosystems; biodiversity over long timescales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes, and the continued application of long-term data for better-informed landscape management. 7. Synthesis Palaeoecology is a vibrant and thriving discipline and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.

Late Wisconsin environments of the Bering Land Bridge

Abstract Late Wisconsin paleobotanical and fossil insect data from the central and northern sectors of the Bering Land Bridge indicate widespread mesic shrub-tundra environments even during the last glacial maximum. Vegetation before the last glacial maximum was a birch-heath-graminoid tundra with few or no steppe elements. Shrubs were not an important element of the vegetation, but were present in small numbers. During the interval 20,000–14,000 yr BP, land-bridge vegetation was dominated by birch-graminoid tundra with small ponds containing aquatic plants. Heaths were relatively unimportant. Insects from this interval were indicative of arctic climate, with drier tundra than during the late glacial. During the late-glacial interval (14,000–11,000 yr BP), land-bridge vegetation was dominated by birch-heath-graminoid tundra with small ponds choked with aquatic plants. The insect record indicates open-ground habitats dominated by mesic tundra. By 11,000 yr BP, insect data suggest that summer temperatures on the emergent Bering Shelf were warmer than present-day upland regions in western Alaska; summer temperatures on the Chukchi Shelf were warmer than the present-day North Slope of Alaska. Contrary to previous hypotheses, we found no evidence of steppe-tundra on the land bridge. New accelerator mass spectrometer (AMS) 14C dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11,000 yr BP.

The chronology of palaeoenvironmental changes during the Last Glacial-Holocene transition: towards an event stratigraphy for the British Isles

The overall aim of the TIGGER IIb project is to increase our understanding of the manner and rates by which ecosystems responded to climate changes during the Last Glacial-Holocene transition. Success in this venture requires better constrained palaeoenvironmental reconstructions than have been achieved thus far, and the TIGGER project focused, in particular, on three main aims: (1) off-setting the limitations of conventional radiocarbon dating, in order to provide a more secure chronology of events; (2) increasing the resolution and precision of palaeoclimatic reconstructions; (3) widening the scope of site-specific palaeoecological investigations. In this paper we focus on the first of these strategies, and describe the progress made in developing a more coherent timescale for the climate history of the Lateglacial period. This has been achieved by using a number of independent methods, including calibration of AMS radiocarbon dates obtained from terrestrial plant macrofossils, MCR estimates of summer temperatures based on coleopteran records, analysis of stable carbon isotope ratios in terrestrial plant macrofossils and tephrochronology. Following Björck et al.s 1998 recommendations, we integrate the new results to construct a provisional event stratigraphy for the Last Glacial-Holocene transition in the British Isles, which is based on a sequence of features that are believed to be time-parallel. This approach is considered to provide a more coherent framework for direct comparison of the palaeoenvironmental evidence from Britain with that from elsewhere.