To demonstrate that incorporating the bioclimatic range of possible contributor plants leads to improved accuracy in interpreting the palaeoclimatic record of taxonomically complex pollen types. ...North Tropical Africa. The geographical ranges of selected African plants were extracted from the literature and geo-referenced. These plant ranges were compared with the pollen percentages obtained from a network of surface sediments. Climate-response surfaces were graphed for each pollen taxon and each corresponding plant species. Several patterns can be identified, including taxa for which the pollen and plant distributions coincide, and others where the range limits diverge. Some pollen types display a reduced climate range compared with that of the corresponding plant species, due to low pollen production and/or dispersal. For other taxa, corresponding to high pollen producers such as pioneer taxa, pollen types display a larger climatic envelope than that of the corresponding plants. The number of species contained in a pollen taxon is an important factor, as the botanical species included in a taxon may have different geographical and climate distributions. The comparison between pollen and plant distributions is an essential step towards more precise vegetation and climate reconstructions in Africa, as it identifies taxa that have a high correspondence between pollen and plant distribution patterns. Our method is a useful tool to reassess biome reconstructions in Africa and to characterize accurately the vegetation and climate conditions at a regional scale, from pollen data.
A pollen diagram from Lac Brulé in southwestern Québec (45°43′09″N, 75°26′32″W, 270 m) provides a late Holocene history of the vegetation. The presence of varved sediments permitted the development ...of a high-resolution (10-year), cross-dated chronology with an estimated error of approximately 1%. During the last 1400 years, the forests were dominated by Tsuga, Fagus, Betula, Acer and Pinus. A peak in microcharcoal and evidence of post-fire succession suggest that the changes in the pollen assemblages around ad 1375 were a consequence of a fire in the region. There was a decrease in pollen influx of several deciduous taxa and Tsuga between ad 1600 and 1700, suggesting a rapid climate change that was significant enough to have affected pollen production of these taxa. This change, associated with the beginning of the ‘Little Ice Age’ in the region, affected the forest composition for the subsequent centuries. A detailed comparison of this pollen record with that from a nearby pollen diagram also prepared at high-temporal resolution shows the ability of pollen records to record short-period climate variations and disturbances.
Pollen, chironomid, and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest Yukon Territory, Canada. The pollen spectra indicate ...herbaceous tundra existed on the landscape from 13.6–11
ka followed by birch shrub tundra until 10
ka. Although
Picea pollen dominated the assemblages after 10
ka, low pollen accumulation rates and
Picea percentages indicate minimal treeline movement through the Holocene. Chironomid accumulation rates provide evidence of millennial-scale climate variability, and the chironomid community responded to rapid climate changes. Ostracodes were found in the late glacial and early Holocene, but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape. Inferred mean July air temperature, total annual precipitation, and water depth indicate a long-term cooling with increasing moisture from the late glacial through the Holocene. During the Younger Dryas (12.9–11.2
ka), cold and dry conditions prevailed. The early and mid-Holocene were warm and dry, with cool, wet conditions after 4
ka, and warm, dry conditions since the end of the Little Ice Age.
A lake sediment core spanning 9900 years, collected from a small lake on western Victoria Island, NWT, Canada, provides a high-resolution record of diatom community dynamics over the Holocene. Ten ...radiocarbon dates and 210Pb dating provided the core chronology. Loss-on-ignition (LOI), magnetic susceptibility, biogenic silica content, and diatom concentrations provided information on changes in the sedimentary environment. LOI gradually increased over the Holocene whereas magnetic susceptibility showed an inverse trend. Biogenic silica content showed three distinct peaks spaced approximately 3000 years apart. Major shifts in diatom assemblages occurred at 8100–8000, 5800–5700, and 3800–3500calyrBP. There is evidence of diatom community response to centennial-scale variations such as the ‘Medieval Warm Period’ (∼1000–700calyrBP), ‘Little Ice Age’ (∼800–150calyrBP) and recent warming. Although recent changes in diatom community composition, productivity, and species richness are apparent they were surpassed at other periods throughout the Holocene. Variations of the taxa within the genera Staurosira, Pseudostaurosira, Fragilaria, and Staurosirella, usually combined into one genus in Arctic lake sediment studies, suggest these taxa provide useful insight into paleonvironmental questions.
Fossil pollen records are well-established indicators of past vegetation changes. The prevalence of pollen across environmental settings including lakes, wetlands, and marine sediments, has made ...palynology one of the most ubiquitous and valuable tools for studying past environmental and climatic change globally for decades. A complementary research focus has been the development of statistical techniques to derive quantitative estimates of climatic conditions from pollen assemblages. This paper reviews the most commonly used statistical techniques and their rationale and seeks to provide a resource to facilitate their inclusion in more palaeoclimatic research. To this end, we first address the fundamental aspects of fossil pollen data that should be considered when undertaking pollen-based climate reconstructions. We then introduce the range of techniques currently available, the history of their development, and the situations in which they can be best employed. We review the literature on how to define robust calibration datasets, produce high-quality reconstructions, and evaluate climate reconstructions, and suggest methods and products that could be developed to facilitate accessibility and global usability. To continue to foster the development and inclusion of pollen climate reconstruction methods, we promote the development of reporting standards. When established, such standards should 1) enable broader application of climate reconstruction techniques, especially in regions where such methods are currently underused, and 2) enable the evaluation and reproduction of individual reconstructions, structuring them for the evolving open-science era, and optimising the use of fossil pollen data as a vital means for the study of past environmental and climatic variability. We also strongly encourage developers and users of palaeoclimate reconstruction methodologies to make associated programming code publicly available, which will further help disseminate these techniques to interested communities.
The Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model was used to quantify Holocene changes in vegetation cover in the deciduous forest of southeastern Quebec, Canada. The ...Extended R-Value (ERV) model was used to obtain relative pollen productivity estimates (PPEs) for eight tree taxa and to determine the relevant source area of pollen (RSAP) for lakes in this ecosystem. Modern vegetation was estimated using pollen data from 16 small (<0.5 km
2
) lakes and a species-level vegetation survey of southern Quebec. The RSAP was estimated to be within 1600 m of the lakes. Tsuga, Fagus, and Quercus were the most productive taxa, and Populus and Acer were the lowest. Reconstructed changes in absolute vegetation cover show a high abundance of Picea followed by Populus in the early Holocene. The reconstructed values for Populus suggest that it was widely distributed across the landscape. Abies and Acer were dominant on the landscape during the late to mid-Holocene, and an increase in Picea during the Neoglacial is more significant than in percentage diagrams. The REVEALS results provide estimates of land-cover change that are more realistic and informative than the use of pollen percentages alone.
Between the initial colonization of North America and the European settlement period, Indigenous American land use practices shaped North American landscapes and ecosystems, but a critical question ...is the extent of these impacts on the land, and how these influenced the distributions of the flora and fauna. The present study addresses this question by estimating the spatial correlation between continental-scale records of fossil pollen and archaeological radiocarbon data, and provides a detailed analysis of the spatiotemporal relationship between palaeo-populations and ten important North American pollen taxa. Maps of Indigenous American population density, based on the Canadian Archaeological Radiocarbon Database, are compared to maps of plant abundance as estimated by pollen records from the Neotoma Paleoecology Database, using nonparametric kernel estimators and cross-correlation techniques. Periods of high spatial cross-correlation (either positive or negative) between population density and plant abundance were identified, but these associations were intermittent and did not increase towards the present. In many cases, high values of population density corresponded with high values of a particular taxon in one region, but simultaneously corresponded with low values in other regions, lessening the overall correlation between the two fields. This analysis suggests that human impacts were not significant enough to be identified at a continental scale, either due to low population numbers or land use, implying significant impacts of ancient human activities on the vegetation were regional rather than continental.
Chironomid and sedimentary records from four lakes in the southwest Yukon reveal that the effects of the White River Ash event on aquatic environments varied with distance from the source vent, with ...sites closer to the source experiencing a greater impact. Upper Fly and Jenny Lakes, located ∼200 km away from the volcano, had the thinnest ash layers. The Upper Fly site showed no response to the fallout of the ash, but at Jenny Lake the ash event affected the lake environment for almost 20 years. Donjek Kettle and Lake WP02, which were closer to the source (∼100 km), had considerably thicker ash layers that substantially affected the aquatic ecosystems. Initial impacts of the tephra on the aquatic environments at these sites lasted about 60 years; however, the chronic effects of the tephra deposition on the chironomid community continued for up to 40 years longer. Chironomid community abundance declined in the lake environments affected by White River Ash fallout following the event. However, species composition remained the same after recovery of the aquatic ecosystem as in the pre-deposition chironomid community. Les enregistrements sédimentaires et les enregistrements de chironomidés en provenance de quatre lacs du sud-ouest du Yukon révèlent que les effets de l'événement de dépôt de cendres de la rivière White sur les milieux aquatiques varient en fonction de la distance qui les sépare de la source de l'évent, les emplacements les plus près de la source ayant subi les conséquences les plus importantes. Les lacs Upper Fly et Jenny, situés à environ 200 km de distance du volcan, présentaient les couches de cendres les plus minces. L'emplacement d'Upper Fly n'affichait aucune réaction en réponse à la tombée des cendres, tandis que dans le cas du lac Jenny, la tombée des cendres a eu des incidences sur l'environnement du lac pendant près d'une vingtaine d'années. Les emplacements de Donjek Kettle et du lac WP02, qui se trouvaient plus près de la source (environ 100 km), présentaient des couches de cendres considérablement plus épaisses, ce qui a eu des effets considérables sur les écosystèmes aquatiques. Les incidences initiales du téphra sur les milieux aquatiques de ces emplacements ont duré une soixantaine d'années. Toutefois, les effets chroniques du dépôt de téphra sur les chironomidés se sont poursuivis pendant une quarantaine d'années de plus. Après le dépôt des cendres, l'abondance des chironomidés a diminué dans les milieux lacustres de la rivière White. Cela dit, les espèces de chironomidés sont demeurées les mêmes après le rétablissement de l'écosystème aquatique qu'avant le dépôt des cendres.
A high-resolution sediment record from Lac Brûlé, southwestern Québec, was studied to determine the effects of long-term climate change and anthropogenic impacts on cladoceran assemblages of the late ...Holocene. Temporal shifts in cladoceran communities were closely associated with known century-scale climatic episodes, namely the Medieval Warm Period (750–1250 CE), the Little Ice Age (1450–1850 CE) and the twentieth-century warming. Forward selection indicated the importance of catchment variables and aquatic primary production in governing cladoceran communities. This suggests that higher trophic levels in Lac Brûlé were responsive to changes in the physical and chemical properties of the lake, perhaps as an indirect consequence of climatic change. The exploitation of the Wallingford-Back Mine in the immediate watershed of Lac Brûlé from 1924 to 1972 CE also had notable impacts on cladoceran assemblages. To strengthen interpretations of the Lac Brûlé record, relationships between cladoceran assemblages and limnological variables were studied in surface samples from 31 lakes from the surrounding region. This spatial analysis identified nutrients (phosphorus and nitrogen) and pH as the most influential variables driving changes in present-day cladoceran communities. However, the performance of cladocera-based inference models was insufficient to quantitatively reconstruct variables in the down-core analysis of Lac Brûlé.
The influence of Native Americans on late-Holocene forests of North America remains a contentious issue, as it is unclear whether vegetation transitions inferred from pollen records are a product of ...prehistoric human disturbance. In southern Ontario, the adoption of maize agriculture coincides with neoglacial cooling, so distinguishing the relative roles of prehistoric people and climatic change in shaping forest composition requires that pollen records be interpreted in a regional context. In this study, we objectively identify pollen records from the southern Ontario region which exhibit periods of significant pre-European anthropogenic disturbance in the context of the archeological record. This enables a comparison of pollen records shaped primarily by climatic cooling with those disturbed by prehistoric human forest clearance. Our results suggest that regional-scale late-Holocene cooling resulted in a gradual and synchronous shift from deciduous to boreal taxa. However, forest clearance by Native Americans resulted in a secondary succession characterized by the replacement of late-successional beech-maple forest with ruderal species, grasses and poplar, followed by mid-successional oak and white pine. This transition consistently coincides in space and time with an increase in archeological records of human occupation. The method we have developed here to distinguish significant prehistoric human impacts could be applied to pollen records in other regions, or on a continental scale.
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