Heikki Seppä
Dados Biográficos
| ID | 5599489 |
|---|---|
| NOME | Heikki Seppä |
| PRENOMES | Heikki |
| SOBRENOME | Seppä |
| ASSINATURA | SEPPÄ H |
| AFILIAÇÕES | University of Helsinki |
| ORCID | 0000-0003-2494-7955 |
| VERIFICADO | Sim |
| TOTAL DE OBRAS | 41 |
| TOTAL DE CITAÇÕES | 139 |
| TOTAL COMO AUTOR | 41 |
| TOTAL COMO EDITOR | 0 |
| PRIMEIRO ANO DE PUBLICAÇÃO | 1998 |
| ANO MAIS RECENTE DE PUBLICAÇÃO | 2019 |
| ÍNDICE H | 7 |
Abrupt Alnus population decline at the end of the first millennium CE in Europe – The event ecology, possible causes and implications
The study, based on the examination of 70 published and unpublished pollen profiles from Poland and supplementary data from the surrounding regions, shows that an abrupt, episodic Alnus population decline at the end of the first millennium CE was a much more widespread event than has been previously reported, spanning large areas of the temperate and boreal zones in Europe. The data from Poland suggest that the decline was roughly synchronous and…
Integrating fire-scar, charcoal and fungal spore data to study fire events in the boreal forest of northern Europe
Fire is a major disturbance agent in the boreal forest, influencing many current and future ecosystem conditions and services. Surprisingly few studies have attempted to improve the accuracy of fire-event reconstructions even though the estimates of the occurrence of past fires may be biased, influencing the reliability of the models employing those data (e.g. C stock, cycle). This study aimed to demonstrate how three types of fire proxies – fire…
Time-varying relationships among oceanic and atmospheric modes
Human responses to early Holocene climate variability in eastern Fennoscandia
Climate of the late Pleistocene and early Holocene in coastal South China inferred from submerged wood samples
Assessing the Importance of Climate Variables for the Spatial Distribution of Modern Pollen Data in China
To assess the importance of climate variables for the distribution of modern pollen data in China, we present a continental-scale dataset consisting of 1374 samples. Boosted regression trees and constrained ordination techniques are employed to quantify the importance of six climate variables (annual precipitation, PANN; actual/potential evapotranspiration ratio, Alpha; mean annual temperature, TANN; mean temperature of the warmest month, MTWA; m…
Human population dynamics in Europe over the Last Glacial Maximum
Significance Despite its importance for understanding genetic, cultural, and linguistic evolution, prehistoric human population history has remained difficult to reconstruct. We show that the dynamics of the human population in Europe from 30,000 to 13,000 y ago can be simulated using ethnographic and paleoclimate data within the climate envelope modeling approach. Correspondence between the population simulation and archaeological data suggests …
Pollen‐based quantitative reconstructions of Holocene regional vegetation cover (plant‐functional types and land‐cover types) in Europe suitable for climate modelling
We present quantitative reconstructions of regional vegetation cover in north‐western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present ( bp )] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to…
Moisture stress of a hydrological year on tree growth in the Tibetan Plateau and surroundings
Investigations of climate-growth interactions can shed light on the response of forest growth to climate change and the dendroclimatic reconstructions. However, most existing studies in the climatically important Tibetan Plateau (TP) and surrouding regions focus on linear growth responses to environmental variation. Herein we investigated both the linear and the nonlinear climate-growth interactions for 152 tree-ring chronologies in the TP and vi…
Quantitative summer and winter temperature reconstructions from pollen and chironomid data between 15 and 8 ka BP in the Baltic–Belarus area
East Asian summer monsoon precipitation variations in China over the last 9500 years
To better understand the long-term changes of the East Asian summer monsoon precipitation ( P jja ), quantitative reconstructions and model simulations are needed. Here, we develop continental-scale pollen-based transfer functions for P jja with weighted averaging–partial least squares (WA-PLS) regression and a Bayesian multinomial regression method. We apply these transfer functions to a set of fossil pollen data from monsoonal China for quantit…
Holocene stand-scale vegetation dynamics and fire history of an old-growth spruce forest in southern Finland
Long-term forest composition and its drivers in taiga forest in NW Russia
Role of forest fires in Holocene stand-scale dynamics in the unmanaged taiga forest of northwestern Russia
Fossil pollen, conifer stomata, and charcoal records for the last 10,000 years were studied from three small hollow sites (Larix Hollow, Mosquito Hollow, and Olga Hollow) located at the modern western range limit of Siberian larch ( Larix sibirica) in northwestern Russia to investigate the role of forest fires in stand-scale dynamics of taiga vegetation. Wavelet coherence analysis was utilized to reveal the significance of fire on the vegetation …
John Birks
We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Eu…
Trees tracking a warmer climate
Palaeoecological records provide a rich source of information to explore how plant distribution ranges respond to climate changes, but their use is complicated by the fact that, especially when based on pollen data, they are often spatially too inaccurate to reliably determine past range limits. To solve this problem, we focus on hazel ( Corylus avellana), a tree species with large and heavy fruits (nuts), which provide firm evidence of the local…
Unexpected Problems in AMS 14 C Dating of Fen Peat
Four fen peat sequences in northern Finland were dated by the accelerator mass spectrometry (AMS) radiocarbon method in order to study past peatland dynamics and carbon accumulation patterns. Initially, plant macrofossils were used for dating. However, the dates were severely disordered, with marked inversions in all sequences. In one 140-cm peat core, for example, all ages fell within a ∼1000-yr time window. Following these unreliable results, a…
Using fire regimes to delineate zones in a high-resolution lake sediment record from the western United States
Paleoenvironmental reconstructions are important for understanding the influence of long-term climate variability on ecosystems and landscape disturbance dynamics. In this paper we explore the linkages among past climate, vegetation, and fire regimes using a high-resolution pollen and charcoal reconstruction from Morris Pond located on the Markagunt Plateau in southwestern Utah, USA. A regime shift detection algorithm was applied to background ch…
The effect of calibration data set selection on quantitative palaeoclimatic reconstructions
Quantitative palaeoclimatic reconstructions based on biological fossils are a major source of information on long-term climatic variability. Such reconstructions typically use some kind of a modern calibration data set describing the variation of the studied biological group in present-day climate space. Here, we explore the effect of calibration data set selection on palaeoclimatic reconstructions, by creating alternate calibration data sets via…
The European Modern Pollen Database (EMPD) project
Modern pollen and land-use relationships in the Taihang mountains, Hebei province, northern China—a first step towards quantitative reconstruction of human-induced land cover changes
Global characterization of the Holocene Thermal Maximum
The Holocene thermal maximum and late-Holocene cooling in the tundra of NE European Russia
To investigate the Holocene climate and treeline dynamics in the European Russian Arctic, we analysed sediment pollen, conifer stomata, and plant macrofossils from Lake Kharinei, a tundra lake near the treeline in the Pechora area. We present quantitative summer temperature reconstructions from Lake Kharinei and Lake Tumbulovaty, a previously studied lake in the same region, using a pollen–climate transfer function based on a new calibration set …
Did the mid-Holocene environmental changes cause the boom and bust of hunter-gatherer population size in eastern Fennoscandia
Prehistoric hunter-gatherer population size is often assumed to follow climatic and other environmental forcings that affect environmental productivity and the availability of food for human foragers. We tested this assumption by studying the co-variation of archaeological and palaeoenvironmental records during the Holocene in eastern Fennoscandia. The reconstruction of population history is based on the summed probability distribution of archaeo…
Comparing different calibration methods (WA/WA-PLS regression and Bayesian modelling) and different-sized calibration sets in pollen-based quantitative climate reconstruction
We compare a Bayesian modelling-based technique with weighted averaging (WA) and weighted averaging-partial least squares (WA-PLS) regression in pollen-based summer temperature transfer function calibration. We test the methods using a new, 113-sample calibration set from Estonia, Lithuania and European Russia, and a Holocene fossil pollen sequence from Lake Kharinei, a previously studied lake in northeast European Russia. We find WA-PLS to outpe…
July mean temperature and annual precipitation trends during the Holocene in the Fennoscandian tree-line area
July mean temperature and annual precipipation during the last 9900 cal. yr BP were recon structed from pollen assemblages preserved in a sediment core from northern Finland. Quantitative recon structions were performed using a modern pollen-climate calibration model based on weighted-averaging partial least squares regression. The predictive ability of the model was evaluated against modern meteoro logical data using leave-one-out cross-validati…
High-resolution reconstruction of wetness dynamics in a southern boreal raised bog, Finland, during the late Holocene
A high-resolution plant macrofossil analysis was applied to investigate wetness dynamics in a southern Finnish boreal bog, Kontolanrahka, during the last 5000 years. The chronological control and the age—depth model were based on 40 AMS radiocarbon dates. Pollen analysis provided information on regional-scale vegetation changes. Macrofossil analysis revealed prominent changes in vegetation assemblages during the late Holocene, indicating fluctuat…
The European Modern Pollen Database (EMPD) project
Did the mid-Holocene environmental changes cause the boom and bust of hunter-gatherer population size in eastern Fennoscandia
Prehistoric hunter-gatherer population size is often assumed to follow climatic and other environmental forcings that affect environmental productivity and the availability of food for human foragers. We tested this assumption by studying the co-variation of archaeological and palaeoenvironmental records during the Holocene in eastern Fennoscandia. The reconstruction of population history is based on the summed probability distribution of archaeo…
A spatio-temporal reconstruction of Holocene temperature change in southern Scandinavia
Holocene mean July ( T Jul ) and mean January ( T Jan ) temperatures were reconstructed at Lake Trehörningen in southwest Sweden using pollen–climate calibration functions and converted into anomalies relative to modern temperatures. The anomalies were applied to 28 meteorological stations in Denmark, with each station adjusted to account for spatial variability in both T Jul and T Jan . The resulting reconstructions were merged to create composi…
Calibrated pollen accumulation rates as a basis for quantitative tree biomass reconstructions
Recent investigations show that the pollen accumulation rate (PAR) of the common tree taxa is directly related to the biomass and, by inference, to the population size of the taxa around the study site. Fossil PAR records preserved in lakes provide therefore a potential proxy for quantitative biomass and population reconstructions. We use the high-resolution PAR records obtained from two accurately dated lake sediment cores in Finland to generate…
Linking past cultural developments to palaeoenvironmental changes in Estonia
Abrupt and consistent responses of aquatic and terrestrial ecosystems to the 8200 cal. yr cold event
A 8400—7700 yr cal. BP section of the sediments of a small lake in southern Finland was studied by high-resolution pollen and cladoceran analyses to examine the response of terrestrial and aquatic ecosystems to the 8200 cal. yr BP cold event. Furthermore, a pollen-based T ann reconstruction and proportions of chydorid ephippia were used to determine changes in temperature and in the length of open-water season during the event. The pollen data, w…
Postglacial trends in palynological richness in the northern Fennoscandian tree-line area and their ecological interpretation
The northern Fennoscandian tree-line area consists of fairly distinct vegetation zones. The pollen stratigraphies of two boreal sites and two tundra sites were studied and the palynological data analysed numerically. The main aim was to measure palynological richness, using rarefaction analysis, and to assess its value in reflecting patterns of past floristic richness. Rates of palynological change were measured using both chord distance and Eucl…
Long-term forest composition and its drivers in taiga forest in NW Russia
Trees tracking a warmer climate
Palaeoecological records provide a rich source of information to explore how plant distribution ranges respond to climate changes, but their use is complicated by the fact that, especially when based on pollen data, they are often spatially too inaccurate to reliably determine past range limits. To solve this problem, we focus on hazel ( Corylus avellana), a tree species with large and heavy fruits (nuts), which provide firm evidence of the local…
Unexpected Problems in AMS 14 C Dating of Fen Peat
Four fen peat sequences in northern Finland were dated by the accelerator mass spectrometry (AMS) radiocarbon method in order to study past peatland dynamics and carbon accumulation patterns. Initially, plant macrofossils were used for dating. However, the dates were severely disordered, with marked inversions in all sequences. In one 140-cm peat core, for example, all ages fell within a ∼1000-yr time window. Following these unreliable results, a…
Abrupt Alnus population decline at the end of the first millennium CE in Europe – The event ecology, possible causes and implications
The study, based on the examination of 70 published and unpublished pollen profiles from Poland and supplementary data from the surrounding regions, shows that an abrupt, episodic Alnus population decline at the end of the first millennium CE was a much more widespread event than has been previously reported, spanning large areas of the temperate and boreal zones in Europe. The data from Poland suggest that the decline was roughly synchronous and…
Integrating fire-scar, charcoal and fungal spore data to study fire events in the boreal forest of northern Europe
Fire is a major disturbance agent in the boreal forest, influencing many current and future ecosystem conditions and services. Surprisingly few studies have attempted to improve the accuracy of fire-event reconstructions even though the estimates of the occurrence of past fires may be biased, influencing the reliability of the models employing those data (e.g. C stock, cycle). This study aimed to demonstrate how three types of fire proxies – fire…
Holocene stand-scale vegetation dynamics and fire history of an old-growth spruce forest in southern Finland
Comparing different calibration methods (WA/WA-PLS regression and Bayesian modelling) and different-sized calibration sets in pollen-based quantitative climate reconstruction
We compare a Bayesian modelling-based technique with weighted averaging (WA) and weighted averaging-partial least squares (WA-PLS) regression in pollen-based summer temperature transfer function calibration. We test the methods using a new, 113-sample calibration set from Estonia, Lithuania and European Russia, and a Holocene fossil pollen sequence from Lake Kharinei, a previously studied lake in northeast European Russia. We find WA-PLS to outpe…
The effect of calibration data set selection on quantitative palaeoclimatic reconstructions
Quantitative palaeoclimatic reconstructions based on biological fossils are a major source of information on long-term climatic variability. Such reconstructions typically use some kind of a modern calibration data set describing the variation of the studied biological group in present-day climate space. Here, we explore the effect of calibration data set selection on palaeoclimatic reconstructions, by creating alternate calibration data sets via…
Modern pollen and land-use relationships in the Taihang mountains, Hebei province, northern China—a first step towards quantitative reconstruction of human-induced land cover changes
Integrated varve and pollen-based temperature reconstruction from Finland
A detailed understanding of decadal to millennial-scale climate changes requires seasonal-scale (summer-winter) reconstructions of past precipitation and temperature fluctuations. Comparing seasonally resolved varve records with pollen-based sum of growing degree-days (GDD) reconstructions from Lake Nautajärvi, we examined the intra-annual nature of climate variability in central southern Finland during the Holocene. The organic varve record and …
Postglacial trends in palynological richness in the northern Fennoscandian tree-line area and their ecological interpretation
The northern Fennoscandian tree-line area consists of fairly distinct vegetation zones. The pollen stratigraphies of two boreal sites and two tundra sites were studied and the palynological data analysed numerically. The main aim was to measure palynological richness, using rarefaction analysis, and to assess its value in reflecting patterns of past floristic richness. Rates of palynological change were measured using both chord distance and Eucl…
July mean temperature and annual precipitation trends during the Holocene in the Fennoscandian tree-line area
July mean temperature and annual precipipation during the last 9900 cal. yr BP were recon structed from pollen assemblages preserved in a sediment core from northern Finland. Quantitative recon structions were performed using a modern pollen-climate calibration model based on weighted-averaging partial least squares regression. The predictive ability of the model was evaluated against modern meteoro logical data using leave-one-out cross-validati…
Holocene Climate Reconstructions from the Fennoscandian Tree-Line Area Based on Pollen Data from Toskaljavri
Due to its location on the eastern North Atlantic seaboard, the Fennoscandian tree-line area is an ideal area to use biological proxies to assess the relative roles of the Scandinavian ice sheet and of oceanic, atmospheric, and astronomic forcings on regional climate history. Here we report pollen-based July mean temperature ( T jul ) and annual precipitation ( P ann ) reconstructions from a sediment core from a high-altitude tree-line lake in no…
Holocene annual mean temperature changes in Estonia and their relationship to solar insolation and atmospheric circulation patterns
We reconstructed annual mean temperature ( T ann ) trends from three radiocarbon-dated Holocene pollen stratigraphies from lake sediments in Estonia, northern Europe. The reconstructions were carried out using a North-European pollen-climate calibration model based on weighted averaging partial least-squares regression. The cross-validated prediction error of the model is 0.89°C and the coefficient of determination between observed modern T ann v…
Abrupt and consistent responses of aquatic and terrestrial ecosystems to the 8200 cal. yr cold event
A 8400—7700 yr cal. BP section of the sediments of a small lake in southern Finland was studied by high-resolution pollen and cladoceran analyses to examine the response of terrestrial and aquatic ecosystems to the 8200 cal. yr BP cold event. Furthermore, a pollen-based T ann reconstruction and proportions of chydorid ephippia were used to determine changes in temperature and in the length of open-water season during the event. The pollen data, w…
High-resolution reconstruction of wetness dynamics in a southern boreal raised bog, Finland, during the late Holocene
A high-resolution plant macrofossil analysis was applied to investigate wetness dynamics in a southern Finnish boreal bog, Kontolanrahka, during the last 5000 years. The chronological control and the age—depth model were based on 40 AMS radiocarbon dates. Pollen analysis provided information on regional-scale vegetation changes. Macrofossil analysis revealed prominent changes in vegetation assemblages during the late Holocene, indicating fluctuat…
Late-Quaternary summer temperature changes in the northern-European tree-line region
We present two new quantitative July mean temperature (T jul ) reconstructions from the Arctic tree-line region in the Kola Peninsula in north-western Russia. The reconstructions are based on fossil pollen records and cover the Younger Dryas stadial and the Holocene. The inferred temperatures are less reliable during the Younger Dryas because of the poorer fit between the fossil pollen samples and the modern samples in the calibration set than du…
Integrated varve and pollen-based temperature reconstruction from Finland
A detailed understanding of decadal to millennial-scale climate changes requires seasonal-scale (summer-winter) reconstructions of past precipitation and temperature fluctuations. Comparing seasonally resolved varve records with pollen-based sum of growing degree-days (GDD) reconstructions from Lake Nautajärvi, we examined the intra-annual nature of climate variability in central southern Finland during the Holocene. The organic varve record and …
Quantitative reconstruction of Holocene precipitation changes in southern Patagonia
Holocene variations in annual precipitation ( P ann ) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance…
Last nine-thousand years of temperature variability in Northern Europe
The threat of future global warming has generated a major interest in quantifying past climate variability on centennial and millennial time-scales. However, palaeoclimatological records are often noisy and arguments about past variability are only possible if they are based on reproducible features in several reliably dated datasets. Here we focus on the last 9000 years, explore the results of 36 Holocene pollen-based July mean and annual mean t…
The spatial and temporal complexity of the Holocene thermal maximum
Recent Warming Reverses Long-Term Arctic Cooling
Climate Reversal The climate and environment of the Arctic have changed drastically over the short course of modern observation. Kaufman et al. (p. 1236 ) synthesized 2000 years of proxy data from lakes above 60° N latitude with complementary ice core and tree ring records, to create a paleoclimate reconstruction for the Arctic with a 10-year resolution. A gradual cooling trend at the start of the record had reversed by the beginning of the 20th …
Calibrated pollen accumulation rates as a basis for quantitative tree biomass reconstructions
Recent investigations show that the pollen accumulation rate (PAR) of the common tree taxa is directly related to the biomass and, by inference, to the population size of the taxa around the study site. Fossil PAR records preserved in lakes provide therefore a potential proxy for quantitative biomass and population reconstructions. We use the high-resolution PAR records obtained from two accurately dated lake sediment cores in Finland to generate…
Linking past cultural developments to palaeoenvironmental changes in Estonia
Holocene land-cover reconstructions for studies on land cover-climate feedbacks
The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (…
The Holocene thermal maximum and late-Holocene cooling in the tundra of NE European Russia
To investigate the Holocene climate and treeline dynamics in the European Russian Arctic, we analysed sediment pollen, conifer stomata, and plant macrofossils from Lake Kharinei, a tundra lake near the treeline in the Pechora area. We present quantitative summer temperature reconstructions from Lake Kharinei and Lake Tumbulovaty, a previously studied lake in the same region, using a pollen–climate transfer function based on a new calibration set …
Did the mid-Holocene environmental changes cause the boom and bust of hunter-gatherer population size in eastern Fennoscandia
Prehistoric hunter-gatherer population size is often assumed to follow climatic and other environmental forcings that affect environmental productivity and the availability of food for human foragers. We tested this assumption by studying the co-variation of archaeological and palaeoenvironmental records during the Holocene in eastern Fennoscandia. The reconstruction of population history is based on the summed probability distribution of archaeo…
Comparing different calibration methods (WA/WA-PLS regression and Bayesian modelling) and different-sized calibration sets in pollen-based quantitative climate reconstruction
We compare a Bayesian modelling-based technique with weighted averaging (WA) and weighted averaging-partial least squares (WA-PLS) regression in pollen-based summer temperature transfer function calibration. We test the methods using a new, 113-sample calibration set from Estonia, Lithuania and European Russia, and a Holocene fossil pollen sequence from Lake Kharinei, a previously studied lake in northeast European Russia. We find WA-PLS to outpe…
A spatio-temporal reconstruction of Holocene temperature change in southern Scandinavia
Holocene mean July ( T Jul ) and mean January ( T Jan ) temperatures were reconstructed at Lake Trehörningen in southwest Sweden using pollen–climate calibration functions and converted into anomalies relative to modern temperatures. The anomalies were applied to 28 meteorological stations in Denmark, with each station adjusted to account for spatial variability in both T Jul and T Jan . The resulting reconstructions were merged to create composi…
Global characterization of the Holocene Thermal Maximum
Using fire regimes to delineate zones in a high-resolution lake sediment record from the western United States
Paleoenvironmental reconstructions are important for understanding the influence of long-term climate variability on ecosystems and landscape disturbance dynamics. In this paper we explore the linkages among past climate, vegetation, and fire regimes using a high-resolution pollen and charcoal reconstruction from Morris Pond located on the Markagunt Plateau in southwestern Utah, USA. A regime shift detection algorithm was applied to background ch…
The effect of calibration data set selection on quantitative palaeoclimatic reconstructions
Quantitative palaeoclimatic reconstructions based on biological fossils are a major source of information on long-term climatic variability. Such reconstructions typically use some kind of a modern calibration data set describing the variation of the studied biological group in present-day climate space. Here, we explore the effect of calibration data set selection on palaeoclimatic reconstructions, by creating alternate calibration data sets via…
The European Modern Pollen Database (EMPD) project
Modern pollen and land-use relationships in the Taihang mountains, Hebei province, northern China—a first step towards quantitative reconstruction of human-induced land cover changes
Role of forest fires in Holocene stand-scale dynamics in the unmanaged taiga forest of northwestern Russia
Fossil pollen, conifer stomata, and charcoal records for the last 10,000 years were studied from three small hollow sites (Larix Hollow, Mosquito Hollow, and Olga Hollow) located at the modern western range limit of Siberian larch ( Larix sibirica) in northwestern Russia to investigate the role of forest fires in stand-scale dynamics of taiga vegetation. Wavelet coherence analysis was utilized to reveal the significance of fire on the vegetation …
Geology and Paleoclimatology Research (38 obras) · Geography (35 obras) · Physical geography (33 obras) · Holocene (30 obras) · Climate change (26 obras) · Biology (21 obras) · Climatology (20 obras) · Tree-ring climate responses (20 obras) · Environmental Science (19 obras) · Ecology (18 obras)