Abstract The hemi-boreal zone, marking North America’s southern boreal forest boundary, has evolved post-glaciation, hosting diverse ecosystems including mixed forests with savannas, grasslands, and ...wetlands. While human, climate, and fire interactions shape vegetation dynamics therein, specific influences remain unclear. Here we unveil 12,000 years of hemi-boreal zone dynamics, exploring wildfire, vegetation, climate, and human population size interactions at such long time scales. Postglacial biomass burning exhibited episodes of persistent elevated activity, and a pivotal shift around 7000 years ago saw the boreal forest transition to an oak-pine barren ecosystem for about 2000 years before reverting. This mid-Holocene shift occurred during a period of more frequent burning and a sudden uptick in mean annual temperatures. Population size of Indigenous peoples mirrored wildfire fluctuations, decreasing with more frequent burning. Anticipated increases of fire activity with climate change are expected to echo transformations observed 7000 years ago, reducing boreal forest extent, and impacting land use.
Latitudinal treeline in northwestern Québec, Canada, is a broad band of forest-tundra between 56 and 58°N. Three new pollen records from the forest-tundra zone were combined with ten ...previously-published records to form a transect of paleoecological data across this treeline. The area was deglaciated ∼6–7 ka, with only a brief period of shrub tundra vegetation in the oldest sediments of all sites. Noticeable values of Populus, Juniperus and Larix pollen percentages were found during this time in the southernmost sites, suggesting they comprised part of the initial plant migration. Maximum Picea pollen percentages were found between 2 and 4 ka across the boreal forest and forest-tundra, with values remaining constant in the boreal forest and decreasing in the forest-tundra in the past 3 ka. Across the entire area, pollen influx decreased in the past 4 ka, and non-arboreal pollen increased in the forest-tundra, suggesting an opening of the forest and decrease in terrestrial production. Charcoal influx also declined, indicating a reduction in fire activity in the past 2–4 ka. Although the treeline has remained in the same average location in the region over the past 6 ka, the strength of the temperature gradient across the frontal zone changed over the course of the Holocene.
•Rapid migration of trees after deglaciation.•Maximum temperatures 5-3ka.•Neoglacial cooling shown by pollen percentages, pollen and charcoal influx.•Climate gradient across treeline changed through time.
Human paleodemographic changes were related to environmental fluctuations for the North American Arctic and boreal region, including Greenland. Using the frequency of archaeological radiocarbon dates ...as a proxy for population size, past changes in population were estimated and quantitatively examined in relation to reconstructions of temperature and sea ice conditions. This analysis was conducted across three spatial scales in order to better identify potential climate impacts on population size: the entire area, four major cultural-environmental regions and sixteen sub-regions. The timing of initial settlement differed by region, and population size fluctuated through time, but there was nevertheless an overall, accelerating increase in most areas. There was a high correspondence between millennial and centennial-scale climate variability and paleodemographic changes across the region, with population size generally increasing during warmer periods and decreasing during cooling episodes. Late Holocene cooling (neoglaciation) triggered a nearly-synchronous population decline across the entire region at 3.9 ka, a time when significant societal disruptions have been identified around the world, and are here shown in the Arctic. Decreasing temperatures and increased sea ice coverage also influenced large-scale migration patterns of Paleo-Inuit peoples as well as their cultural evolution. The growth of Paleo-Inuit populations after 3 ka during continued climate cooling is consistent with archaeological evidence suggesting Paleo-Inuit technological change enabled adaptations to increased sea ice.
•Multi-scale analysis of human-environment interactions discerns local and regional population dynamics.•Climate changes caused increases and decreases in population in the Arctic and Subarctic.•Neoglaciation triggered continental-scale population decline across the north.•Population density underwent long-term growth despite climate-induced regional decreases.
A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55°N at the last glacial maximum (LGM) and mid‐Holocene (6000 years B.P.). The ...pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf‐shrub tundra, erect dwarf‐shrub tundra, and low‐ and high‐shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra‐forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid‐Holocene the tundra‐forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (∼200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (∼200 km). Low‐ and high‐shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf‐shrub, erect dwarf‐shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low‐ and high‐shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.
This study presents a diatom-based analysis of the post-glacial Holocene environmental history at Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post-glacial diatom assemblages ...(10 200–10 000 cal yr BP) consisted mainly of small, benthic fragilarioid taxa. Poor diatom preservation in the early Holocene (~10 000–6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediment records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid-Holocene. During this time period, cooling causing changes in lake ice phenology was likely a major driver of the reconstructed mid-Holocene pH decline. Watershed processes, including reduced fluxes of base cations as the rate of sediment accumulation slowed, may also be contributors to long-term shifts in lake water pH and associated changes in diatom assemblages. The uppermost sediments in the Lake RS29 record were characterized by abrupt declines in Aulacoseira alpigena and increases in benthic diatom taxa Cyclotella sensu lato, suggesting an increase in lake water pH and longer ice-free seasons.
This study investigates the spatio-temporal postglacial development of the vegetation in the northwestern part of the forest-tundra of northern Québec, Canada. Six lake sediment cores and 59 modern ...sediment samples were collected in an area of 16 by 7 km and analyzed for pollen and charcoal. Following a brief herb and shrub tundra period and a period with abundant Alnus, Picea mariana grew in the region for at least the past 4000 years, but there was a gradient across the area, with Picea growing to the west but not toward the east. The period of maximum Picea abundance varied between sites, but was generally between 1500 and 2500 years ago. Neoglacial cooling resulted in a decrease in Picea on the landscape, but the timing of the decline at any site depended on removal of Picea by fire. There was a gradient in Picea abundance across this study area, which resulted in a reconstructed spatial July temperature gradient of ∼1 °C across this 16 km region. In spite of the importance of fire in affecting local Picea populations around any lake, the paleoclimate reconstructions showed a long-term neoglacial cooling of ∼1 °C over the past 3800 cal yr BP, with superimposed century-scale fluctuations of ∼0.2 °C, corresponding to the Little Ice Age, the Medieval Warm Period, the Dark Ages Cold Period and the Roman Warm Period. High-resolution pollen records can therefore be used to reconstruct not only regional vegetation and climate history, but also local differences within small areas.
•Six postglacial pollen and charcoal records in a 16 × 7 km area in NW Québec.•Impact of the interaction of fire and climate on the vegetation shown.•Vegetation and climate gradient across this area quantified.•Neoglacial cooling and century scale fluctuations recorded.
The North American prairie-forest border is a major biogeographic boundary ultimately determined by the macroclimate. Climate variability during the Holocene affected the vegetation in this area, but ...impacts on human paleodemography are unknown. At a regional scale, community structure is partly determined by fire, however the extent to which anthropogenic burning has affected fire regimes over the Holocene is unresolved. This study investigates the interaction between climate variability, vegetation changes, fire regimes, and human population levels in the North American prairie-forest ecotone during the Holocene using information from publically-available paleoenvironmental databases. Biomass burning was associated with moisture and vegetation more than with human population size, suggesting anthropogenic burning did not significantly influence the composition and location of the prairie-forest border. Human population growth rates were impacted by sociocultural developments and environmental changes, with most changes in subsistence strategies occurring during climate regime shifts. The development of the Eastern Agricultural Complex (5.0 – 3.8 ka) and the transition to more mesic conditions after 4.0 ka facilitated long-term population growth. The arrival of maize and the bow-and-arrow at 2.2 and 1.6 ka, respectively, resulted in increased population growth, and after 1 ka, maize agriculture intensification, aided by a warmer climate, accelerated population growth. The collapse of the city of Cahokia is linked to a wider population decline across the Midwest precipitated by the Medieval Warm Period – Little Ice Age transition. Populations across a significant portion of North America were in decline at the time of European colonization. These findings provide evidence against a large-scale early Anthropocene in North America, and illustrate the importance of climate change in influencing human history.
•Holocene population levels were impacted by sociocultural and environmental changes.•No evidence of human regional-scale impact on prairie-forest border or fire regime.•Cahokia’s collapse occurred during population declines across the Midwest.•Population across much of North America was decreasing prior to European arrival.
A high‐resolution diatom sequence was developed from continuously laminated lake sediments in southwestern Québec, which spanned the Holocene (~11,000 yr). General and species‐specific changes in the ...diatom record were synchronous with patterns of vegetation succession inferred from regional palynological studies, demonstrating significant influences of terrestrial ecosystems on lake water chemistry and aquatic biota. Principal components analysis was used to identify three major diatom biostratigraphic zones corresponding broadly to early, mid‐, and late Holocene climate intervals. Benthic alkaliphilus diatom taxa were abundant when the landscape was a Picea‐dominated woodland in the early Holocene (11.1–8.0 ka), and when climate conditions were inferred as relatively cool and dry. In the mid‐Holocene (8.0–3.6 ka), warmer temperatures resulted in a stabilization of soils and forests in the catchment area. Shade‐tolerant tree species (Tsuga, Fagus, and Betula) increased during this time, and planktonic diatom taxa (Discostella stelligera and Fragilaria tenera) were abundant in the lake. The well‐known decline in Tsuga across eastern North America between 6.0 and 5.0 ka corresponded to a shift toward more nutrient‐rich lake conditions for several centuries, indicated by an increase in benthic diatom taxa and a lower ratio of chrysophytes relative to diatoms. Neoglacial cooling in the late Holocene (3.6 ka to present) triggered an initial decline in D. stelligera, which later recovered as a result of nutrient inputs that were associated with increased abundances of hardwood, deciduous species (Betula and Alnus) in the catchment. In addition to providing a high‐resolution record of lake ontogeny for the region, the full Holocene record from this lake adds a new perspective on the spatial extent of regional aridity during the Medieval Warm Period (1.2–0.8 ka).
Archaeological radiocarbon (14C) dates are a fundamental source of information documenting patterns in paleodemographic change from prehistoric to modern times. Several open access databases ...(Canadian Archaeological Radiocarbon Database, Radiocarbon Palaeolithic Europe Database, CONTEXT, RAdiocarbon Dates ONline, and AustArch) and publications which include lists of dates provide easy access to archaeological 14C data, presently totalling over 70,000 dates worldwide. Some parts of the world are more extensively sampled than others including North America, Australia and China, whereas in others the databases have not yet been prepared. A comparison of frequency distributions of 14C dates from North America and Australia to modeled estimates of historical population growth for these continents from the HYDE 3.1 database shows similarities, providing confidence in long-term estimates of population growth using both methods. Our capacity to study global demographic change is currently limited by the spatiotemporal completeness of regional 14C databases. These results suggest the systematic collection and entry of dates into an openly-accessible, global 14C database will allow for significant advances to be made in archaeology, anthropology and Quaternary paleogeography.
Seven species of freshwater ostracodes were identified from the sediments of 43 lakes on eight islands across the Canadian Arctic Archipelago. No ostracodes were encountered in the sediments of ...almost half of the lakes, and most were found at sites that had higher alkalinity. Several taxa endemic to Arctic regions are found across the Arctic Archipelago, including Candona rectangulata Aim, Limnocythere liporeticulata Delorme, and Tonnacypris glacialis Sars. The distributions of Cytherissa lacustris Sars, Cyclocypris globosa Sars, Limnocythere sappaensis Staplin, and Limnocythere (Limnocytherind) camera Delorme are more limited; this fact is attributed to differences in ion composition and concentrations /// Sept espèces d'ostracodes d'eau douce ont été identifiées à partir des sédiments de 43 lacs répartis dans huit îles de l'archipel Arctique canadien. Aucun ostracode n'a été décelé dans les sédiments de près de la moitié des lacs, et la plupart ont été trouvés dans des lieux ayant un taux d'alcalinité plus élevé. Plusieurs taxons endémiques aux régions de l'Arctique se retrouvent à la grandeur de l'archipel Arctique, dont le Candona rectangulata Alm, le Limnocythere liporeticulata Delorme et le Tonnacypris glacialis Sars. Les répartitions de Cytherissa lacustris Sars, de Cyclocypris globosa Sars, de Limnocythere sappaensis Staplin et de Limnocythere (Limnocytherind) camera Delorme sont plus restreintes, ce qui est attribuable aux différences sur le plan de la composition et des concentrations en ions
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