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ABSTRACT: Quantitative reconstructions of mean July temperatures (T
jul) based on new and previously published pollen-stratigraphical data covering the last 2000years from 11lakes in northern
Fennoscandia and the Kola Peninsula are presented. T
jul values are based on a previously published pollen-climate transfer function for the region with a root-mean-square error
of prediction (RMSEP) of 0.99°C. The most obvious trend in the inferred temperatures from all sites is the general decrease
in T
jul during the last 2000years. Pollen-inferred T
jul values on average 0.18±0.56°C (n=91) higher than present (where “present” refers to the last three decades based on pollen-inferred T
jul in core-top samples) are indicated between 0 and 1100 AD (2000–850calyear BP), and temperatures −0.2±0.47°C (n=78) below present are inferred between 1100 and 1900 AD (850–50calyear BP). No consistent temperature peak is observed
during the ‘Medieval Warm Period’, ca. 900–1200 AD (1100–750calyear BP), but the cooler period between 1100 and 1900 AD
(850–50calyear BP) corresponds in general with the ‘Little Ice Age’ (LIA). Consistently with independent stable isotopic
data, the composite pollen-based record suggests that the coldest periods of the LIA date to 1500–1600 AD (450–350calyear
BP) and 1800–1850 AD (150–100calyear BP). An abrupt warming occurred at about 1900 AD and the twentieth century is the warmest
century since about 1000 AD (950calyear BP).
Journal of Paleolimnology 04/2012; 41(1):43-56. · 1.90 Impact Factor
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ABSTRACT: A study on the taphonomy of Cladocera was carried out in a small (9ha), oligotrophic mountain loch, Loch Coire Fionnaraich
(LCFR) in northwest Scotland. Four approaches were used. First, the fossil assemblage of Cladocera in the core-top sample
taken from the deepest basin (14m) of the loch were compared with the fossil assemblages of Cladocera in surface sediments
along eight depth transects with samples taken at 2, 5, 8 and 11m, respectively. The results of the deposition of remains
of individual Cladocera and of the PCA ordination showed that littoral Cladocera were dominant in the 2m-depth samples, while
the planktonic Cladocera dominated the deeper water (8, 11m and core-top) samples. Second, the fossil assemblages of Cladocera
in the core-top sample were compared with the assemblages in a sediment trap sample. The core-top sample showed a better representation
of the cladoceran taxa present in the loch than the trap sample, but rare taxa were missing in the core sample. Third, the
fossil assemblages of Cladocera in the core sample were compared with the contemporary assemblages in the source samples derived
from seasonal sampling across all habitats (macrophyte, sand, boulder) over 2years. Only a small proportion of Cladocera
in the source samples was represented by the fossil assemblages in the core sample. Finally, ‘integrated’ approach samples
(spatial, trap, source and core together) were compared using PCA. The Cladocera in the core-top sample were closely related
to the trap and surface sediment samples, but weakly related to the source samples. The overall results indicate that biases
may occur whilst reconstructing the past environmental change based on the fossil assemblages of Cladocera in the core sample
taken from the deepest basin of the lake.
Journal of Paleolimnology 04/2012; 38(2):157-181. · 1.90 Impact Factor
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ABSTRACT: UV-B radiation currently represents c. 1.5% of incoming solar radiation. However, significant changes are known to have occurred in the amount of incoming radiation both on recent and on geological timescales. Until now it has not been possible to reconstruct a detailed measure of UV-B radiation beyond c. 150 yr ago. Here, we studied the suitability of fossil Pinus spp. pollen to record variations in UV-B flux through time. In view of the large size of the grain and its long fossil history, we hypothesized that this grain could provide a good proxy for recording past variations in UV-B flux. Two key objectives were addressed: to determine whether there was, similar to other studied species, a clear relationship between UV-B-absorbing compounds in the sporopollenin of extant pollen and the magnitude of UV-B radiation to which it had been exposed; and to determine whether these compounds could be extracted from a small enough sample size of fossil pollen to make reconstruction of a continuous record through time a realistic prospect. Preliminary results indicate the excellent potential of this species for providing a quantitative record of UV-B through time. Using this technique, we present the first record of UV-B flux during the last 9500 yr from a site near Bergen, Norway.
New Phytologist 08/2011; 192(2):553-60. · 6.64 Impact Factor
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ABSTRACT: Aim This study explores the relationship between orchid species richness along elevational gradients in the central and eastern Himalaya. Specifically, we aimed to test predictions of maximum richness at different elevational levels for orchid species geographically restricted to central and eastern Himalaya (endemics), and total orchid richness, including different life forms. We then compared and assessed climatic factors together with area as causal explanations for the observed patterns.Location Nepal (100–5200 m a.s.l.), Bhutan (100–5200 m a.s.l.), and adjacent regions of India, i.e. Sikkim and Darjeeling.Methods We used published data on the distribution of orchids to interpolate presence between maximum and minimum recorded elevations in 100-m elevational zones. These patterns were compared with previously published patterns for other plant groups, which were derived in the same way. Descriptive regressions with metres above sea level (m a.s.l.) as the independent variable were performed using nonparametric generalized additive models (GAMs), whereas tests of the diversity models were carried out using parametric generalized linear models (GLMs).Results A hump-shaped relationship between orchid species richness and elevation was observed in Nepal and Bhutan, with maximum richness at 1600 m a.s.l. corresponding to c. 16 °C mean annual temperature. The richness of orchid species that are endemic to central and eastern Himalaya showed a bimodal pattern. Richness of endemic epiphytes peaked at elevation zones similar to those for total richness, but the peak in numbers of endemic terrestrial species occurred at a higher elevation.Main conclusions This study shows that climatic variables (temperature and precipitation) provide a good potential explanation for orchid species richness along the Himalayan elevational gradient, even when the effect of area is considered. The principal elevational peak in richness of central and eastern Himalayan endemics was consistent with the peak in total orchid richness, but maximum terrestrial endemic richness occurred at higher elevations.
Journal of Biogeography 05/2011; 38(9):1821 - 1833. · 4.54 Impact Factor
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T. Giesecke,
K. D. Bennett, H. J. B. Birks,
E. Bozilova,
A. Feurdean,
W. Finsinger,
C.A. Froyd,
M. Rösch,
H. Seppä,
S. Tonkov,
V. Valsecchi,
S. Wolters
Quaternary Science Reviews 01/2011; 30:2805-2814. doi:10.1016/j.quascirev.2011.06.014. · 3.97 Impact Factor
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ABSTRACT: Fossil records are replete with examples of long-term biotic responses to past climate change. One particularly useful set of records are those preserved in lake and marine sediments, recording both climate changes and corresponding biotic responses. Recently there has been increasing focus on the need for conservation of ecological and evolutionary processes in the face of climate change. We review key areas where palaeoecological archives contribute to this conservation goal, namely: (i) determination of rates and nature of biodiversity response to climate change; (ii) climate processes responsible for ecological thresholds; (iii) identification of ecological resilience to climate change; and (iv) management of novel ecosystems. We stress the importance of long-term palaeoecological data in fully understanding contemporary and future biotic responses.
Trends in Ecology & Evolution 10/2010; 25(10):583-91. · 15.75 Impact Factor
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Gaillard M.-J,
Sugita S,
Mazier F,
Trondman A.-K,
Broström A,
Hickler T,
J. O. Kaplan,
Kjellström E,
Kokfelt U,
Kuneš P, [......],
Lagerås P,
Latałowa M,
Leydet M,
Lechterbeck J,
Lindbladh M,
Odgaard B,
Peglar S,
Segerström U,
H. von Stedingk,
Seppä H
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ABSTRACT: 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 (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/land-cover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs "grassland" and "agricultural land" at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.
Climate of the Past 07/2010; 6(4):483-499. · 3.51 Impact Factor
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The Open Ecology Journal. 01/2010; 3:68-110.
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ABSTRACT: Throughout Earth’s history there have been temporal and spatial variations in the amount of visible and ultraviolet radiation received by ecosystems. This paper examines if temporal changes in these forms of energy receipt could have influenced the tempo and mode of plant diversity and speciation, focusing in particular upon Cenozoic time-scales. Evidence for changing patterns of plant diversity and speciation apparent in various fossil records and molecular phylogenies are considered alongside calculated changes in thermal and solar ultraviolet energy (specifically UV-B) over the past 50 Myr. We suggest that changes in thermal energy influx (amount and variability) affected the tempo of evolution through its influence upon community dynamics (e.g. population size, diversity, turnover, extinctions). It was not only the amount of thermal energy but also variability in its flux that may have influenced these processes, and ultimately the rate of diversification. We suggest that variations in UV-B would have influenced the mode and tempo of speciation through changes to genome stability during intervals of elevated UV-B. We argue, therefore, that although variability in thermal energy and UV-B fluxes through time may lead to the same end-point (changing the rate of diversification), the processes responsible are very different and both need to be considered when linking evolutionary processes to energy flux.
Journal of Biogeography 04/2009; 36(9):1630 - 1644. · 4.54 Impact Factor
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ABSTRACT: 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 temperature reconstructions from Northern Europe by stacking them to create summary curves, and compare them with a high-resolution, summary chironomid-based temperature record and other independent palaeoclimate records. The stacked records show that the "Holocene Thermal Maximum" in the region dates to 8000 to 4800 cal yr BP and that the "8.2 event" and the "Little Ice Age" at 500–100 cal yr BP are the clearest cold episodes during the Holocene. In addition, a more detailed analysis of the last 5000 years pinpoints centennial-scale climate variability with cold anomalies at 3800–3000 and 500–100 cal yr BP, a long, warmer period around 2000 cal yr BP, and a marked warming since the mid 19th century. The colder (warmer) anomalies are associated with increased (decreased) humidity over the northern European mainland, consistent with the modern high correlation between cold (warm) and humid (dry) modes of summer weather in the region. A comparison with the key proxy records reflecting the main forcing factors does not support the hypothesis that solar variability is the cause of the late-Holocene centennial-scale temperature changes. We suggest that the reconstructed anomalies are typical of Northern Europe and their occurrence may be related to the oceanic and atmospheric circulation variability in the North Atlantic – North-European region.
Climate of the Past. 01/2009;
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01/2009; 28:1309-1316.
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K.F. Helmens,
J. A. A. Bos,
S. Engels,
C.J. van Meerbeeck,
S.P. Boncke,
H. Renssen,
O. Heiri,
S.J. Brooks,
H. Seppä, H. J. B. Birks,
B. Wohlfahrt
Geology. 01/2007; 35(11):987-990.
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H. Seppa, H. J. B. Birks,
T. Giesecke,
D. Hammarlund,
T. Alenius,
K. Antonsson,
A. E. Bjune,
M. Heikkila,
G. M. MacDonald,
A. E. K. Ojala,
R. J. Telford,
S. Veski
01/2007; 3:225-236.
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01/2007; 316.
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ABSTRACT: Ecosystems change in response to factors such as climate variability, invasions, and wildfires. Most records used to assess such change are based on short-term ecological data or satellite imagery spanning only a few decades. In many instances it is impossible to disentangle natural variability from other, potentially significant trends in these records, partly because of their short time scale. We summarize recent studies that show how paleoecological records can be used to provide a longer temporal perspective to address specific conservation issues relating to biological invasions, wildfires, climate change, and determination of natural variability. The use of such records can reduce much of the uncertainty surrounding the question of what is "natural" and thereby start to provide important guidance for long-term management and conservation.
Science 12/2006; 314(5803):1261-5. · 31.20 Impact Factor
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ABSTRACT: In contrast with macroorganisms, whose geographical ranges are typically restricted, many microbial species appear to have cosmopolitan distributions. This observation has been explained as a consequence of ubiquitous dispersal caused by the enormous population sizes of microbial species. Recently, this "everything is everywhere, but, the environment selects" theory has been challenged by the detection of considerable regional genetic variability within microbial morphospecies. We demonstrate that, contrary to what is expected under ubiquitous dispersal, evidence of regional-scale metacommunity processes can be detected in microbial morphospecies. Our results imply that the microbial and macrobial world are structured by analogous processes.
Science 06/2006; 312(5776):1015. · 31.20 Impact Factor
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ABSTRACT: Pither & Aarssen (2005) propose a null model approach to assess the proportion of niche specialist taxa along ecological gradients. They apply this methodology to a large data set of lacustrine diatom assemblages and conclude that a majority of the taxa are generalists on a pH gradient. This conflicts with previous work, which shows that many diatom taxa have a statistically significant relationship with pH. We demonstrate the methods used by Pither & Aarssen (2005) have a high Type II error for rare taxa, and that this problem is compounded by the non-uniform sampling of the pH gradient which effectively precludes acid-lake specialist diatoms from being recognized as such. We re-analyse the data used by Pither & Aarssen (2005) and show that most of the diatoms have a statistically significant relationship with pH, and we thus refute their conclusions that few diatom species are specialists.
Ecology Letters 05/2006; 9(4):E1-5; discussion E6-12. · 17.56 Impact Factor
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ABSTRACT: In this study, we analyse the cumulative rate of compositional change along an altitudinal gradient in the Swiss Alps for
three different groups of aquatic organisms – Cladocera, chironomids, and diatoms. In particular, we are interested in the
magnitude of unusually large changes in species composition that allows the detection of critical ecotones for each of these
three organism groups. The estimated rate-of-change is the distance in ordination space using principal coordinate analysis
based on chord distance and chi-square distance. These analyses highlight the cumulative rate-of-change and the cumulative
relative rate-of-change, as the chi-square distance is relative to the total species composition. We found that the major
changes in taxonomic composition for the three organism groups and therefore also the major ecotones are just below the modern
tree-line (1900–2000m a.s.l.), which may indirectly be an effect of the tree-line. For diatoms and Cladocera (only chi-square
distance) there is also an ecotone at 2055m a.s.l., which may be a direct or indirect response to climate. Further, the ecotone
region below the modern tree-line is much wider for chironomids, with an extension downwards due to a shift in relative abundance
patterns. For diatoms there is a stronger rate-of-change above 1650m a.s.l. when chi-square distance is used. Coupled with
the even distribution of diatom richness, this suggests that at higher altitudes the change is more strongly associated with
a few species becoming dominant compared to lower elevations. Hence, there are considerable differences among the three organism
groups, suggesting that different environmental factors may influence the rates of compositional change within and among groups.
This supports the general usefulness of multi-proxy studies, namely the study of several independent groups of organisms to
reconstruct past environmental conditions but also points to the importance of careful site selection in such studies.
Journal of Paleolimnology 03/2006; 35(3):507-518. · 1.90 Impact Factor
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01/2005; 15:612-618.
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01/2005; 24:2173-2179.
