36 results
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2. Special Paper: Comparison of Post-Glacial Molluscan and Vegetational Successions from a Radiocarbon-Dated Tufa Sequence in Oxfordshire
- Author
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Preece, R. C. and Day, S. P.
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- 1994
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3. Post-glacial patterns in vegetation dynamics in Romania: homogenization or differentiation?
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Feurdean, Angelica, Willis, Katherine J., Parr, Catherine L., Tanţău, Ioan, and Fărca, Sorina
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VEGETATION dynamics ,GLACIAL climates ,BIODIVERSITY conservation ,PRINCIPAL components analysis - Abstract
Aim This paper examines eight fossil pollen datasets from Romania with the aim of exploring regional and elevational patterns in site similarity throughout the Holocene. In particular, we aim to determine whether there are clear intervals of homogenization/differentiation and to ascertain the potential driving factors. Location Romania. Methods Qualitative (pollen diagrams) and numerical methods including principal components analysis and Bray-Curtis similarity analyses were used. Results We found strong variability in the past vegetation dynamics during the Holocene. Bray-Curtis similarity analyses show large fluctuations in vegetation similarity and distinct periods of homogenization and differentiation throughout the Holocene. The magnitude and length of these periods appear quite variable in time, but the significant ones can be delimited as follows: (1) differentiation between 11,250 and 11,000 cal. yr bp, 10,000 and 9750 cal. yr bp, 6000 and 5750 cal. yr bp, 2500 and 2250 cal. yr bp, and especially over the last 200 years; and (2) homogenization between 9750 and 9500 cal. yr bp, and 2750 and 2500 cal. yr bp, with more stable periods between 9000 and 7750 cal. yr bp, 4750 and 3500 cal. yr bp, and 2000 and 1000 cal. yr bp. Main conclusions First, periods of biotic homogenization that occurred before significant anthropogenic impact on vegetation demonstrate that not all homogenization is a product of anthropogenic change: it can also be driven by natural causes. In fact, recent human impact (over the last 200 years) appears to have resulted in increased regional differentiation and not in homogenization - a result that contradicts most studies based on more modern, short-term records. Second, both abiotic (climate and disturbance) and biotic factors are likely drivers of intervals of differentiation and homogenization. We suggest that differentiation may be triggered primarily by climate changes and disturbances (mostly natural pre-2500 cal. yr bp and human-induced thereafter), whereas homogenization may be driven predominantly by biotic interactions (e.g. immigration and interspecific competition). Third, this long-term study raises awareness that assessments of pattern in vegetation homogenization/differentiation may depend on the specific time period and length of investigation. Long-term investigations through multiple generations are likely to yield particularly useful information on the mechanisms and effects of biotic homogenization. [ABSTRACT FROM AUTHOR]
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- 2010
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4. Holocene global warming and the origin of the Neotropical Gran Sabana in the Venezuelan Guayana.
- Author
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Rull, Valentí
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VEGETATION & climate ,HOLOCENE paleoclimatology ,GLOBAL warming ,CHARCOAL ,POLLEN ,SAVANNAS ,PALEOCLIMATOLOGY ,PLEISTOCENE-Holocene boundary - Abstract
Aim The assumedly anomalous occurrence of savannas and forest–savanna mosaics in the Gran Sabana – a neotropical region under a climate more suitable for tropical rain forests – has been attributed to a variety of historical, climatic, and anthropogenic factors. This paper describes a previously undocumented shift in vegetation and climate that occurred during the early Holocene, and evaluates its significance for the understanding of the origin of the Gran Sabana vegetation. Location A treeless savanna locality of the Gran Sabana (4°30′–6°45′ N and 60°34′–62°50′ W), in the Venezuelan Guayana of northern South America, at the headwaters of the Caroní river, one of the major tributaries of the Orinoco river. Methods Pollen and charcoal analysis of a previously dated peat section spanning from about the Pleistocene/Holocene boundary until the present. Results Mesothermic cloud forests dominated by Catostemma (Bombacaceae) occupied the site around the Pleistocene/Holocene boundary. During the early Holocene, a progressive but relatively rapid trend towards savanna vegetation occurred, and eventually the former cloud forests were replaced by a treeless savanna. Some time after the establishment of savannas, a marked increase in charcoal particles indicates the occurrence of the first local fires. Main conclusions The occurrence of cloud forests at the Pleistocene/Holocene boundary contradicts the historical hypothesis according to which the Gran Sabana is a relict of the hypothetical widespread savannas that have been assumed to have dominated the region during the last glaciation. The first local fires recorded in the Holocene were on savanna vegetation, which is against the hypothesis of fire as the triggering factor for the establishment of these savannas. Climate change, in the form of global warming and a persistently drier climate, emerges as the most probable cause for the forest–savanna turnover. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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5. The Holocene spread of Picea abies (L.) Karst. in Fennoscandia and adjacent areas.
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Giesecke, Thomas and Bennett, K. D.
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FORESTS & forestry ,HOLOCENE stratigraphic geology ,POPULATION density ,FOSSIL fuels ,NORWAY spruce - Abstract
The Holocene spread of Picea abies in Fennoscandia is well established from many sites and thus provides an opportunity for detailed study of the dynamics of tree spread and population expansion. Early- and mid-Holocene macrofossil evidence for presence of P. abies in Fennoscandia has questioned traditional interpretations of the timing and direction of its spread. This paper aims to determine when, from where and by which pathways P. abies spread into Fennoscandia. Understanding the character and dynamics of this spread may give insight into the general understanding of Holocene tree spread. The north-western distribution of P. abies in Europe, including Norway, Sweden, Finland, Estonia, Latvia, Lithuania, north-western Russia, parts of Byelorussia and Poland. Holocene pollen diagrams with independent dating control were collected from this region. The timing of the onset of the continuous curve, the timing of the rise of the curve, the first appearance of frequencies of 1%, 3%, 5%, and 10%, as well as timing and the maximum amount of P. abies pollen, was obtained from these pollen diagrams. A GIS analysis was used to display the data and interpolate ages over the area under investigation. Maps are presented showing a clear ESE to WNW trend in the spread of P. abies for all characters interpolated. The timing of the rise of the curve was difficult to use as sites east of the Baltic have slowly rising P. abies frequencies while the western sites often show a rapid rise. The spread of P. abies in Fennoscandia and adjacent areas can be separated into two phases: (i) A rapid early Holocene spread out of Byelorussia and northern Russia at low population density giving rise to small outpost populations, possibly as far west as the Scandes Mountains. (ii) A mid- to late Holocene front-like spread at high population densities moving from east to west into the Baltic Republics and Finland, into northern Scandinavia and then moving south and west towards its present-day distributional limits. [ABSTRACT FROM AUTHOR]
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- 2004
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6. Boreal tree taxa in the central Scandes during the Late-Glacial: implications for Late-Quaternary forest history.
- Author
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Kullman, Leif
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TREES ,FOSSILS ,DOWNY birch ,NORWAY spruce ,SCOTS pine - Abstract
Aim This paper seeks to elucidate the first post-glacial arrival of tree species to high elevations in the Scandes. This enables testing of general theories concerning glacial refugia, immigration routes and palaeoclimate. Location The study site, 1360 m a.s.l., was close to the summit of Mt Åreskutan in the alpine region of the southern Swedish Scandes, 400–500 m above modern tree-limits. Methods Tree megafossils (trunks, roots, cones) were retrieved (and radiocarbon-dated) from the ground surface in the forefields of receding `perennial' snow-patches. This approach allows elevational range-margin reconstructions to be made with an accuracy not possible with any other method. Results and conclusions Megafossils were recovered substantially higher and earlier than previously recorded or inferred for tree growth in this part of Europe. The species were Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman, Picea abies (L.) Karst. and Pinus sylvestris (L.). The oldest dates obtained are c . 14,000, 11,000 and 11,700 BP for these species, respectively. For the first time, explicit evidence of tree growth in the Late-Glacial (including the Younger Dryas stadial) is demonstrated for central/northern Scandinavia. The swift appearance of boreal tree species at high northern latitudes and altitudes on the western fringe of Scandinavia and near the most extended margin of the Weichselian ice sheet hypothetically suggests that the first immigration of the trees considered here was from the west. Glacial refugia for these species (other plants and animals as well) on the exposed continental shelf areas west and southwest of Norway is hypothesized. By extension, the results fit into a more general pattern, suggesting the presence of boreal and temperate trees quite close to the full glacial (Weichselian) ice margins in central Europe. Thus, the Quaternary forest and landscape history of Europe seems more complex than previously believed. [ABSTRACT FROM AUTHOR]
- Published
- 2002
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7. Early Holocene plant and animal remains from North-east Greenland.
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Bennike, Ole, Björck, Svante, Böcher, Jens, Hansen, Louise, Heinemeier, Jan, and Wohlfarth, Barbara
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PLANT remains (Archaeology) ,ZOOARCHAEOLOGY ,HOLOCENE stratigraphic geology - Abstract
Summary Aim The aim of this paper is to describe and interpret early Holocene floras and faunas. Location The floras and faunas come from various localities in North-east Greenland. Methods Sediment samples were wet sieved, and macrofossils picked out and dated by the AMS radiocarbon-dating method. Results Sediments, dated to the first centuries after the last glacial stage came to an abrupt end, contain a macroflora of bryophytes and a few herbs, and we suggest that these plant remains represent a pioneer vegetation entirely without woody plants. The named species of herbs are either confined to the northern parts of Greenland at present, or they become increasingly more important towards the north. Crowberry is the oldest woody plant recovered; it was present at 10.4 cal. ka BP, and it appears to have been common during the early Holocene in East Greenland. Main conclusions We suggest that the majority of the extant flora of vascular plants of East Greenland arrived by long distance dispersal during the Holocene. Some species may also have arrived during the late-glacial, and a few hardy species that are adapted to low summer temperatures may have survived the last glacial stage in nonglaciated areas. Some hardy animals may also have survived, but the majority of the fauna are considered Holocene immigrants. We suggest that migrating birds and storms, perhaps in combination, are under-appreciated dispersal vectors. [ABSTRACT FROM AUTHOR]
- Published
- 1999
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8. Mid-Holocene vegetation diversity in eastern Cumbria.
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Skinner, C. and Brown, A. G.
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PLANT diversity ,HOLOCENE stratigraphic geology - Abstract
SummaryThe concept of biodiversity can operate at several different ecological levels from that of the Global ecosystem to the genetic diversity of a single species. This paper focuses on the beta-type diversity of vegetation communities at the intra and inter-regional scale, using five mid-Holocene (Neolithic) pollen diagrams from eastern Cumbria (c. 500 km
2 centred on the Eden valley). The sites were selected in order to include the variation in both soil/rock type and altitude within the study area, ranging from the Eden valley and southern limestone plateau to the foothills and summits of the western edge of the Pennines. The local pollen component which is dominant in these small sites, is used to determine intra-regional vegetation diversity for a time-slice in the Neolithic. Simple statistical methods are used to compare sites and as a measure of intra-regional vegetation-type diversity. This is compared with estimates of the community diversity for the British Isles during the same period. The results suggest that the intra-regional vegetation diversity is comparable to that of Northern England, and it is related to variation in both altitude and soil type. There are some differences, for example the steepness of the western face of the Pennines is probably responsible for a lack of the pine dominated zone, and pedological constraints probably prevented the full development of woodland on the limestone plateau at the south of the study area. The open landscape of the limestone plateau acted as a refuge for late glacial herbaceous taxa prior to their re-expansion into the wider landscape after widespread deforestation and arable cultivation. The results have implications for both the mapping of past vegetation at the national scale and for landscape archaeology. [ABSTRACT FROM AUTHOR]- Published
- 1999
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9. Winter temperature and forest cover have shaped red deer distribution in Europe and the Ural Mountains since the Late Pleistocene
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Pavel A. Kosintsev, Karolina Doan, Pavel Hulva, Dariusz Krasnodębski, Jessie Woodbridge, Vesna Dimitrijević, Bogdan Ridush, Ninna Manaseryan, Ana Stanković, Katerina Trantalidou, Daniel Makowiecki, Theodor F. Obadă, Ralph Fyfe, Magdalena Niedziałkowska, Maciej Sykut, Natalia Piotrowska, Alesia Arabey, Oleksandr Kovalchuk, Ulrich Schmölcke, Grzegorz Lipecki, Maxim Charniauski, Marine Arakelyan, Sławomira Pawełczyk, Paweł Mackiewicz, Marcin Górny, Eve Rannamäe, Krzysztof Stefaniak, Jarosław Wilczyński, Vadim V. Titov, Urmas Saarma, Adrian Bălășescu, and Bogumiła Jędrzejewska
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0106 biological sciences ,SPATIAL DISTRIBUTION ,010506 paleontology ,LAST GLACIAL MAXIMUM REFUGIA ,EUROPE ,Pleistocene ,Range (biology) ,FOREST HABITAT ,CLIMATE CHANGE ,DEER ,PLEISTOCENE ,Species distribution ,JANUARY TEMPERATURE ,PALAEOECOLOGY ,010603 evolutionary biology ,01 natural sciences ,Last Glacial Maximum refugia ,Deforestation ,HOLOCENE ,CLIMATE CONDITIONS ,TEMPERATURE EFFECT ,Ecology, Evolution, Behavior and Systematics ,Holocene ,0105 earth and related environmental sciences ,URALS ,UNGULATES ,Ecology ,CERVUS ELAPHUS ,UNGULATA ,PALEOECOLOGY ,Last Glacial Maximum ,15. Life on land ,PLEISTOCENE-HOLOCENE BOUNDARY ,EXPANSION-CONTRACTION MODEL ,ENVIRONMENTAL NICHE MODELLING ,LAST GLACIAL MAXIMUM ,Geography ,FOREST COVER ,TEMPERATE CLIMATIC ZONE ,13. Climate action ,SUBFOSSIL ,WEST ASIA ,Paleoecology ,RADIOCARBON DATING ,WINTER - Abstract
Aim: The Expansion-Contraction model has been used to explain the responses of species to climatic changes. During periods of unfavourable climatic conditions, species retreat to refugia from where they may later expand. This paper focuses on the palaeoecology of red deer over the past 54 ka across Europe and the Urals, to reveal patterns of change in their range and explore the role of environmental conditions in determining their distribution. Location: Europe and western Asia to 63°E. Taxon: Red deer (Cervus elaphus). Methods: We collected 984 records of radiocarbon-dated red deer subfossils from the Late Pleistocene and the Holocene, including 93 original dates. For each deer sample we compiled climatic and biome type data for the corresponding time intervals. Results: During the last 54 ka changes in red deer range in Europe and the Urals were asynchronous and differed between western and eastern Europe and western Asia due to different environmental conditions in those regions. The range of suitable areas for deer during the Last Glacial Maximum (LGM) was larger than previously thought and covered vast regions not only in southern but also in western and eastern Europe. Throughout the period investigated the majority of specimens inhabited forests in the temperate climatic zone. The contribution of forests in deer localities significantly decreased during the last 4 ka, due to deforestation of Europe caused by humans. Mean January temperature was the main limiting factor for species distribution. Over 90% of the samples were found in areas where mean January temperature was above −10°C. Main conclusions: Red deer response to climatic oscillations are in agreement with the Expansion-Contraction model but in contradiction to the statement of only the southernmost LGM refugia of the species. During the last 54 ka red deer occurred mostly in forests of the temperate climatic zone. © 2020 John Wiley & Sons Ltd. European Social Fund, Grant/Award Number: UDA-POKL.04.01.01-00-072/09-00; University of Wroclaw, Grant/Award Number: 0410/2990/18; Institute of Environmental Biology, University of Wrocław, Grant/Award Number: 0410/2990/18; Mammal Research Institute Polish Academy of Sciences; Narodowe Centrum Nauki , Grant/Award Number: DEC-2013/11/B/NZ8/00888 and UMO-2016/23/B/HS3/00387; Romanian National Authority for Scientific Research, UEFISCDI, Grant/Award Number: PN-IIIP4-ID-PCE-2016-0676; National Centre for Atmospheric Science and the Centre for Environmental Data Analysis, UK; Faunal Database of the Stage Three Project; Leverhulme Trust, Grant/Award Number: F00568W.
- Published
- 2020
10. Late Pleistocene and Holocene distribution of Mytilus edulis in the Barents Sea region and its palaeoclimatic implications.
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Hansen, Jesper, Hanken, Nils-Martin, Nielsen, Jan K., Nielsen, Jesper K., and Thomsen, Elsebeth
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MYTILUS edulis ,MUSSELS ,SEASHELLS ,SPECIES distribution ,PALEOCLIMATOLOGY - Abstract
For decades, subfossil shells of the bivalve Mytilus edulis Linnaeus, 1758 in Svalbard have been taken as evidence of higher surface temperatures during the early Holocene because the modern northern occurrence of this mollusc was, until recently, in the southern Barents Sea. Here, we elucidate and discuss the spatial and temporal Late Pleistocene and Holocene distribution of the species within the entire Barents Sea region. The Barents Sea region. Radiocarbon dates of Mytilus shells from the Barents Sea region and information about the present distribution of the species were compiled, including two new radiocarbon dates from north-eastern Spitsbergen. The dataset was divided into time slices, each covering 1000 years, and compared with Holocene temperature variations, ocean current systems and present-day temperature patterns. Maps show the Late Pleistocene and Holocene spatial and temporal distribution of Mytilus edulis in the Barents Sea region. M. edulis was already present in northern Norway about 14,000 cal. yr . It appeared at western Spitsbergen about 11,000 cal. yr , and slowly spread to the rest of the archipelago. The maximum distribution in the region was reached 10,000-7000 cal. yr , coinciding with the Holocene climatic optimum. The species gradually disappeared in the late Holocene and became absent from the northern and eastern parts of the region 3000-1000 cal. yr . Today, M. edulis lives in the southern part and has begun to recolonize the northern parts. The time slices illustrate strong connections between the ocean current regimes, the climate and the distribution of M. edulis. The species settled in the southern part of the Barents Sea region several thousand years before it spread to the northern part during the Holocene climatic optimum. It may even have been completely absent from the region for a short time during the late Holocene cold period. The Holocene distribution of Mytilus implies that the underlying pattern of coastal sea surface temperatures in the region was very stable. [ABSTRACT FROM AUTHOR]
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- 2011
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11. The origin and temporal development of an ancient cultural landscape.
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Fletcher, Michael-Shawn and Thomas, Ian
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CULTURAL landscapes ,VEGETATION management ,FORESTS & forestry ,MOORS (Wetlands) ,FOSSIL pollen - Abstract
Aim To reconstruct the Late Glacial and Holocene vegetation history of western Tasmania and to test the long-held notion of a replacement of forest by moorland during the mid to late Holocene in western Tasmania, Australia. Location Western Tasmania, Australia. Methods Fossil pollen data were screened with a modern pollen dataset using detrended correspondence analysis and charcoal data were analysed using significance tests. Results At the landscape scale, the distribution of vegetation types in western Tasmania has remained remarkably stable through the post-glacial period. Open moorland has dominated the landscape since the Late Glacial, while rain forest expanded at that time in to areas which it occupies today. Vegetation development in the Holocene is markedly different and charcoal values are significantly higher when compared with those in previous interglacial periods. Main conclusions The dominant paradigm of a replacement of rain forest by moorland across western Tasmania during the mid to late Holocene is not supported by this regional analysis. The arrival of humans in Tasmania during the Last Glacial Stage provided an ignition source that was independent of climate, and burning by humans through the Late Glacial period deflected vegetation development and facilitated the establishment of open moorland in regions occupied by rain forest during previous interglacial periods. It is concluded that the present dominance of the landscape of western Tasmania by open moorland is the direct result of human activity during the Late Glacial and that this region represents an ancient cultural landscape. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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12. Modelling late Quaternary changes in plant distribution, vegetation and climate using pollen data from Georgia, Caucasus.
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Connor, Simon E. and Kvavadze, Eliso V.
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CLIMATIC factors of phytogeography ,POLLEN ,NUMERICAL analysis ,PLEISTOCENE-Holocene boundary ,QUATERNARY paleoclimatology ,MIXED forests ,ECOLOGY - Abstract
Aim To use pollen data, numerical analysis and modelling to reconstruct late Quaternary vegetation and climate in a complex, mountainous environment. Location Georgia (Caucasus region). Methods Pollen data were assembled from various sources and used to map: (1) changing frequencies of individual taxa; (2) vegetation changes; and (3) reconstructed climatic parameters for the past 14,000 years. Numerical analyses were performed using two-way indicator species analysis (twinspan), detrended correspondence analysis (DCA), the modern analogue technique (MAT) and weighted averaging (WA). Results Mapping of pollen taxa showed that Chenopodiaceae, Artemisia and Ephedra were most abundant in the study area during the late-glacial. Betula and Corylus expanded during the early Holocene, yielding to Abies, Carpinus, Fagus, Quercus and Castanea. Picea, Pinus, Juglans and Ostrya-type expanded during the late Holocene. Mixed forests grew in the moist, Black Sea refugium throughout the late Quaternary. Elsewhere in Georgia, the Pleistocene–Holocene transition is recorded as a shift from desert-steppes to oak-xerophyte communities and mixed forests. This kind of vegetation remained relatively stable until the mid–late Holocene, when coniferous forests and mountain grasslands advanced. DCA showed that rainfall was most strongly correlated with pollen composition in the study area ( r
2 = 0.55). No temperature signal was detected. A weighted-averaging transfer function linking pollen percentages to annual precipitation was selected over a MAT model as it performed better when applied to a validation data set. Rainfall reconstructions indicate widespread aridity at the terminal Pleistocene, followed by a gradual increase in precipitation, peaking during the mid Holocene (7000–4000 cal. yrbp) and generally decreasing thereafter. Main conclusions On a regional scale, the results confirm those from previous studies of palaeovegetation and palaeoclimate in Western Asia. On a local scale, reconstructions from individual sites often diverge from the regional trend because of edaphic changes, ecological succession, human impacts and other disturbances. Some of these factors are probably responsible for the increasing heterogeneity of Georgia’s vegetation in the latter half of the Holocene. [ABSTRACT FROM AUTHOR]- Published
- 2009
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13. The Late Holocene extinction of Pinus sylvestris in the western Cantabrian Range (Spain).
- Author
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Rubiales, Juan M., García-Amorena, Ignacio, García Álvarez, Salvia, and Gómez Manzaneque, Fernando
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SCOTS pine ,PYRENEAN oak ,HOLOCENE stratigraphic geology ,VEGETATION dynamics ,BIOGEOGRAPHY ,CLIMATE change ,SPECIES distribution ,RADIOCARBON dating - Abstract
Aim To reconstruct the historical biogeography of Pinus sylvestris in the Cantabrian Range (Iberian Peninsula) during the Holocene, and to consider the interactions between vegetation dynamics, climate change and the role of man in the present-day distribution of the species. Location The study site is a mire (1300 m a.s.l.) at Vega de Viejos, on a south-facing slope of the western Cantabrian Range, Spain. The region’s present-day landscape is almost treeless, with the exception of some patches of Quercus pyrenaica and a few copses of Salix and Betula along stream banks. Methods Tree macrofossils from Vega de Viejos were studied by transmitted light and dark-field reflection microscopy; strobili were subjected to comparative morphological analyses. Two Pinus macrofossils were dated by conventional
14 C methods. Results The taxonomic accuracy achieved in the identification of the macrofossils provided new information regarding the Holocene history of Pinus sylvestris in this territory. Ninety-five cones of this species were identified; in fact, more than 80% of the 36 identified wood remains were of Pinus gr. sylvestris. Radiocarbon dating revealed that the forest to which the fossils belonged was present until at least 2170 ± 50 yr bp– its disappearance was therefore relatively recent. Main conclusions Pinus sylvestris suffered long-term isolation, and after the Würm glacial period tended to migrate towards the east. In western Iberia, a temperate climate and autogenic succession favoured broadleaved taxa at the expense of Pinus. Late Holocene human disturbances may have further accelerated the decline of P. sylvestris; in the Cantabrian Range, only a few stands on southern slopes have persisted until the present day. The history of the capercaillie ( Tetrao urogallus), a bird characteristic of pure or mixed Palaeartic coniferous forests, was almost certainly affected by the demise of these forests in this area. Cantabrian capercaillies are the only members of this species that live in purely deciduous forests, perhaps a recent adaptation to the regional extinction of pines. Today’s P. sylvestris and capercaillie populations are now highly fragmented and their future, given the predictions of global climate change, is uncertain. [ABSTRACT FROM AUTHOR]- Published
- 2008
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14. Historical climate modelling predicts patterns of current biodiversity in the Brazilian Atlantic forest.
- Author
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Carnaval, Ana Carolina and Moritz, Craig
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BIODIVERSITY ,FOREST microclimatology ,CLIMATOLOGY ,PHYLOGEOGRAPHY ,BIOGEOGRAPHY ,HOLOCENE paleoclimatology ,PALYNOLOGY - Abstract
Aim We aim to propose validated, spatially explicit hypotheses for the late Quaternary distribution of the Brazilian Atlantic forest, and thereby provide a framework for integrating analyses of species and genetic diversity in the region. Location The Atlantic forest, stretching along the Brazilian coast. Methods We model the spatial range of the forest under three climatic scenarios (current climate, 6000 and 21,000 years ago) with BIOCLIM and MAXENT. Historically stable areas or refugia are identified as the set of grid cells for which forest presence is inferred in all models and time projections. To validate inferred refugia, we test whether our models are matched by the current distribution of the forest and by fossil pollen data. We then investigate whether the location of inferred forest refugia is consistent with current patterns of species endemism and existing phylogeographical data. Results Forest models agree with pollen records and predict a large area of historical forest stability in the central corridor (Bahia), as well as a smaller refuge (Pernambuco) along the Brazilian coast, matching current centres of endemism in multiple taxa and mtDNA diversity patterns in a subset of the species examined. Less historical stability is predicted in coastal areas south of the Doce river, which agrees with most phylogeographical studies in that region. Yet some widely distributed taxa show high endemism in the southern Atlantic forest. This may be due to limitations of the modelling approach, differences in ecology and dispersal capability, historical processes not contemplated by the current study or inadequacy of the available test data sets. Main conclusions Palaeoclimatic models predict the presence of historical forest refugia in the Atlantic rain forest and suggest spatial variation in persistence of forests through the Pleistocene, predicting patterns of biodiversity in several local taxa. The results point to the need for further studies to document genetic and species endemism in the relatively poorly known and highly impacted areas of Atlantic rain forests of north-eastern Brazil. [ABSTRACT FROM AUTHOR]
- Published
- 2008
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15. Environmental setting of human migrations in the circum-Pacific region.
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Pope, Kevin O. and Terrell, John E.
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EMIGRATION & immigration ,HUMAN settlements ,BIOGEOGRAPHY ,CLIMATE change ,ABSOLUTE sea level change - Abstract
Aim To assess the genetic and archaeological evidence for the migration of modern humans out of Africa to the circum-Pacific region and compare the migration patterns with Late Pleistocene and Holocene changes in sea level and climate. Location Southern and eastern Asia, Australia, and Oceania. Methods Review of the literature and detailed compilations of data on early human settlements, sea level, and climate change. Results The expansion of modern humans out of Africa, following a coastal route into southern Asia, was initially thwarted by a series of large and abrupt environmental changes. A period of relatively stable climate and sea level from c. 45,000 yrbp to 40,000 yrbp supported a rapid coastal expansion of modern humans throughout much of Southeast Asia, enabling them to reach the coasts of northeast Russia and Japan by 38,000–37,000 yrbp. Further northwards, migrations were delayed by cold northern climates, which began to deteriorate rapidly after 33,000 yrbp. Human migrations along the coast of the Bering Sea into the New World appear to have occurred much later, c. 14,000 yrbp, probably by people from central Asia who were better adapted to cold northern climates. Cold, dry climates and rapidly changing sea levels leading into and out of the Last Glacial Maximum inhibited coastal settlement, and many of the sites occupied prior to 33,000 yrbp were abandoned. After 16,000 yrbp, the sea-level rise slowed enough to permit coastal ecosystems to develop and coasts to be re-colonized, but abrupt changes in climate and sea level inhibited this development until after 12,000 yrbp. Between 12,000 yrbp and 7000 yrbp there was a dramatic increase in reef and estuary/lagoon ecosystems, concurrent with a major expansion of coastal settlements. This early Holocene increase in coastal environments and the concomitant expansion of human coastal-resource exploitation were followed by corresponding declines in both phenomena in the mid-Holocene, c. 6000–4000 yrbp. This decline in coastal resources is linked to the drop in sea level throughout the Pacific, which may have caused the widespread population dislocations that ultimately led to the human expansion throughout Oceania. Main conclusions Climate and sea-level changes played a central role in the peopling of the circum-Pacific region. [ABSTRACT FROM AUTHOR]
- Published
- 2008
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16. Holocene vegetation history of the Sahel: pollen, sedimentological and geochemical data from Jikariya Lake, north-eastern Nigeria.
- Author
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Waller, Martyn P., Street-Perrott, F. Alayne, and Hongya Wang
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VEGETATION & climate ,SEDIMENTOLOGY ,ANALYTICAL geochemistry ,POLLEN ,CHARCOAL - Abstract
Aim This study aims to separate regional and local controls on Holocene vegetation development and examine how well pollen records reflect climate change in a semi-arid region. The relative importance of climate and human activity as agents of vegetation change in the Sahel during the late Holocene is also considered. Location Jikariya Lake, an inter-dune depression in the Manga Grasslands of north-eastern Nigeria. Methods Pollen and charcoal were used to provide a record of Holocene vegetation history. Palaeoclimate and hydrological changes were reconstructed from sedimentary and geochemical data. Regional and local influences were separated by comparing the evidence obtained from Jikariya Lake with previously published data from the Manga Grasslands. Results The Manga Grasslands experienced a prolonged wet period during the early and mid-Holocene, during which swamp forest vegetation with Guinean affinities ( Alchornea, Syzygium, Uapaca) occupied the inter-dune depressions. However, variation in the pollen records between sites suggests that their establishment was dependent on conditions being locally favourable, rather than being directly coupled to regional climate. The pollen records from the Manga Grasslands are more consistent in suggesting the colonization of the dunefields by trees associated with Sudanian savanna (Combretaceae, Detarium) c. 8700 cal. yrbp. The Jikariya Lake pollen data are in accordance with the sedimentological and geochemical data from the region in indicating that the onset of arid conditions occurred progressively during the late Holocene (from c. 4700 cal. yrbp). Abrupt changes in pollen stratigraphy, recorded at other Manga Grasslands sites 3500 cal. yrbp, appear to be the product of the local passing of ecological thresholds. The dunefield vegetation (Sahelian savanna) appears to have been resilient to (or at least palynologically silent regarding) to the climatic variability of the late Holocene. Main conclusions While climate appears to have been the primary control on vegetation development in the Manga Grasslands during the Holocene, local conditions (particularly depression size and sand influx) had a strong influence on the timing of pollen stratigraphic changes. Anthropogenic influences are difficult to detect, even during the late Holocene. [ABSTRACT FROM AUTHOR]
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- 2007
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17. A regional study of Holocene climate change and human occupation in Peruvian Amazonia.
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Bush, M. B., Silman, M. R., and Listopad, C. M. C. S.
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CLIMATE change ,HUMAN settlements ,ANTHROPOGENIC effects on nature ,LAKES ,CHARCOAL ,POLLEN ,PALYNOLOGY ,TOPOLOGY ,BIODIVERSITY - Abstract
Aim To investigate the influence of Holocene climatic and human-induced changes on a region of high biodiversity in southern Peruvian Amazonia. Location Four palaeoecological records from separate lakes within a lake district close to the modern city of Puerto Maldonado, Peru. Results The lakes provide a palaeoecological record spanning the last 8200 years. A mid-Holocene dry event is documented in all of the records that extend back > 6000 years. The dry event appears to have lasted from c. 7200 yrbp until c. 3300 yrbp. The onset of wetter conditions coincides with the formation of the youngest of the four lakes. The earliest occupation of these sites is inferred from the presence of charcoal at 7200 yrbp, and the first crop pollen is found at 3630 yrbp. Lakes that were regularly occupied were colonized soon after they formed. A reduction in charcoal concentration and the absence of crop pollen after c. 500 bp in all lakes is consistent with site abandonment following conquest. Main conclusions The mid-Holocene dry event is suggested to be part of a time-transgressive drying that tracked from north to south in both the Andes and the Amazon lowlands. The last millennium may represent the period of highest sustained lake levels within the Holocene. The proximity of the four lakes allows a landscape-scale analysis of the spatial extent of human disturbance centred on a known site of human occupation and reveals the highly localized nature of pre-Columbian anthropogenic disturbance in Amazonian landscapes. Inferences regarding widespread pre-Columbian landscape modification by indigenous peoples must take into account key site attributes, such as seasonality and proximity to rivers. [ABSTRACT FROM AUTHOR]
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- 2007
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18. Post-glacial changes in spatial patterns of vegetation across southern New England.
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Wyatt Oswald, W., Faison, Edward K., Foster, David R., Doughty, Elaine D., Hall, Brian R., and Hansen, Barbara C. S.
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VEGETATION & climate ,BIOCLIMATOLOGY ,CLIMATE & biogeography ,BOTANY ,PALYNOLOGY ,PALEOBOTANY ,VEGETATION mapping ,CLIMATE change ,CLIMATOLOGY - Abstract
Aim We analysed lake-sediment pollen records from eight sites in southern New England to address: (1) regional variation in ecological responses to post-glacial climatic changes, (2) landscape-scale vegetational heterogeneity at different times in the past, and (3) environmental and ecological controls on spatial patterns of vegetation. Location The eight study sites are located in southern New England in the states of Massachusetts and Connecticut. The sites span a climatic and vegetational gradient from the lowland areas of eastern Massachusetts and Connecticut to the uplands of north-central and western Massachusetts. Tsuga canadensis and Fagus grandifolia are abundant in the upland area, while Quercus, Carya and Pinus species have higher abundances in the lowlands. Methods We collected sediment cores from three lakes in eastern and north-central Massachusetts (Berry East, Blood and Little Royalston Ponds). Pollen records from those sites were compared with previously published pollen data from five other sites. Multivariate data analysis (non-metric multi-dimensional scaling) was used to compare the pollen spectra of these sites through time. Results Our analyses revealed a sequence of vegetational responses to climate changes occurring across southern New England during the past 14,000 calibrated radiocarbon years before present (cal yrbp). Pollen assemblages at all sites were dominated by Picea and Pinus banksiana between 14,000 and 11,500 cal yrbp; by Pinus strobus from 11,500 to 10,500 cal yrbp; and by P. strobus and Tsuga between 10,500 and 9500 cal yrbp. At 9500–8000 cal yrbp, however, vegetation composition began to differentiate between lowland and upland sites. Lowland sites had higher percentages of Quercus pollen, whereas Tsuga abundance was higher at the upland sites. This spatial heterogeneity strengthened between 8000 and 5500 cal yrbp, when Fagus became abundant in the uplands and Quercus pollen percentages increased further in the lowland records. The differentiation of upland and lowland vegetation zones remained strong during the mid-Holocene Tsuga decline (5500–3500 cal yrbp), but the pattern weakened during the late-Holocene (3500–300 cal yrbp) and European-settlement intervals. Within-group similarity declined in response to the uneven late-Holocene expansion of Castanea, while between-group similarity increased due to homogenization of the regional vegetation by forest clearance and ongoing disturbances. Main conclusions The regional gradient of vegetation composition across southern New England was first established between 9500 and 8000 cal yrbp. The spatial heterogeneity of the vegetation may have arisen at that time in response to the development or strengthening of the regional climatic gradient. Alternatively, the differentiation of upland and lowland vegetation types may have occurred as the climate ameliorated and an increasing number of species arrived in the region, arranging themselves in progressively more complex vegetation patterns across relatively stationary environmental gradients. The emergence of a regional vegetational gradient in southern New England may be a manifestation of the increasing number of species and more finely divided resource gradient. [ABSTRACT FROM AUTHOR]
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- 2007
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19. Post-glacial migration of silver fir ( Abies alba Mill.) in the south-western Alps.
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Muller, Serge D., Nakagawa, Takeshi, de Beaulieu, Jacques-Louis, Court-Picon, Mona, Carcaillet, Christopher, Miramont, Cécile, Roiron, Paul, Boutterin, Clément, Ali, Adam A., and Bruneton, Hélène
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SILVER fir ,FIR ,PINACEAE ,PALEOBOTANY ,BOTANY ,PALYNOLOGY ,BIOGEOMORPHOLOGY ,GEOMORPHOLOGY ,VEGETATION mapping - Abstract
Aim Previous studies have failed to reconstruct the regional post-glacial migration pattern of Abies alba in southern France. Based on the first exhaustive compilation of palaeoecological data in this region, we present the state-of-the-art and attempt to synthesize the available information concerning glacial refugia and post-glacial migration, and analyse the information with regard to climate and orography. Location South-western Alps and adjacent areas, southern France. Methods The work compiles the available palaeoecological data in the south-western Alps (52 sites, 290 radiocarbon dates). The post-glacial migration pattern of Abies alba is reconstructed based on 22 selected palynological analyses (11 well-dated reference sites and 11 supplementary ones). Results The geographical patterns of approaching area limit, immigration and expansion are reconstructed at the scale of the southern French Alps. Main conclusions Despite previous assertions, the evidence of refugia in southern France is non-existent. The late-glacial records of fir pollen, previously interpreted in French Mediterranean regions and on adjacent foot-hills as possibly reflecting regional refugia, most probably correspond to reworking phenomena or long-distance pollen transport. Fir migration, originating in the Apennine refugia and through the south-western extremity of the Alps, was extremely rapid in the southern French Alps, only spanning a few centuries between 10,100 and 9800 cal. yrbp. The subsequent spread of fir populations was controlled by local parameters, such as the aridity of the inner valleys, which resulted in a delayed expansion in comparison to other regions. Abies almost disappeared from the south-western Alps during the Roman era, around 2000 cal. yrbp. [ABSTRACT FROM AUTHOR]
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- 2007
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20. Holocene vegetation and climate change from near Lake Pedder, south-west Tasmania, Australia.
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Fletcher, Michael-Shawn and Thomas, Ian
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HOLOCENE stratigraphic geology ,VEGETATION & climate ,CLIMATE change ,SURVEYS ,RAIN forests ,HEATHLANDS ,MOUNTAIN plants ,FORESTS & forestry - Abstract
Aim To use surface pollen and vegetation relationships to aid the interpretation of a Holocene pollen record. Location South-west Tasmania, Australia. Methods A survey was undertaken of surface-pollen samples from the major regional vegetation types: alpine, rain forest and moorland. Relationships between vegetation type and surface-pollen representation were analysed usingtwinspan classification and ordination. A core was retrieved from moorland vegetation, and interpretation of the fossil pollen sequence was aided using relationships detected in our surface-pollen analysis. Results Regional vegetation types are reflected in the pollen rain of south-west Tasmania, despite the over-representation of important rain forest tree species in samples from non-forest sites.twinspan classification of the surface-pollen samples identified the following indicator pollen taxa for each vegetation type: Astelia alpina (alpine); Lagarostrobos franklinii (rain forest); Leptospermum and Melaleuca (moorland). Detrended correspondence analysis of the surface-pollen samples clearly separates samples from each vegetation type. Correlation of the ordination axes with environmental data identified a dominant temperature/altitudinal gradient in the surface-pollen data ( R = 0.852/0.844). Application of the results of the surface-pollen analysis to the fossil sequence revealed that fire-promoted moorland has dominated the local environment around the core site for the entire Holocene. Changes in fossil pollen composition also suggest that temperatures increased through the Late Glacial to peak in the mid-Holocene and declined thereafter, a trend consistent with other sites in the region. Main conclusions Pollen spectra can successfully be used to predict local vegetation in south-west Tasmania. At least this part of inland south-west Tasmania has remained forest-free throughout the Holocene, conflicting with the dominant palaeoecological paradigm of a mid-Holocene dominated by rain forest. A comparison with pollen records from moorland vegetation across the region suggests that fire-promoted moorland has dominated the landscape since the Late Glacial. We suggest that burning by people through the Late Glacial (if not earlier) facilitated the spread of moorland throughout the region, greatly restricting the expansion of rain forest. The continued influence of fire throughout the Holocene in this perennially wet landscape argues for a revision of the dominant human-occupation model that depicts an abandonment of the interior of south-west Tasmania in the Late Glacial in response to the expansion of rain forest. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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21. Pinus cembra L. (arolla pine), a common tree in the inner French Alps since the early Holocene and above the present tree line: a synthesis based on charcoal data from soils and travertines.
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Ali, Adam A., Carcaillet, Christopher, Talon, Brigitte, Roiron, Paul, and Terral, Jean-Frédéric
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BIOGEOGRAPHY ,BIOGEOMORPHOLOGY ,PINACEAE ,MASS spectrometry ,SPECTRUM analysis - Abstract
In this study, charcoal-based data for Pinus cembra L . (arolla pine) were gathered from soil and travertine sequences in order to reconstruct its historical biogeography at the landscape level in the inner western Alps during the Holocene. The study sites are located between 1700 and 2990 m a.s.l., in the southern (Queyras Massif and Ubaye Valley) and the northern (Maurienne Valley) parts of the inner French Alps. Charcoal fragments were extracted from sediments by water sieving, using meshes of 5, 2, 0.8 and 0.4 mm. The charcoal mass of P. cembra was determined in each charcoal assemblage. Accelerator mass spectrometry and conventional
14 C measurements were used to date the fragments. Supported by 4014 C datings, the fragments show that, over 2000 m a.s.l., P. cembra accounts for around 40% (mean value) of identified fragments. Data reveal that arolla pine once extended between 260 and 375 m above the present-day local tree lines. It was established in the southern and the northern French Alps from at least c. 9000 and 6000 cal yr bp, respectively. While present-day populations of P. cembra are very fragmented in the inner French Alps, charcoal records indicate large past occurrences of this tree since the early Holocene. Human disturbance since the Neolithic seems to be the main reason for the regression of the arolla pine woodlands. On the south-facing slopes of the study sites, currently deforested, this species extended up to 2800 m a.s.l. In the northern areas, charcoal records of the P. cembra expansion are consistent with the regional pollen archives, but in the southern massifs charcoal records indicate its presence c. 2600 years earlier than other palaeobotanical studies suggest. This discrepancy highlights the necessity to crosscheck data using several different proxies in order to assess the validity of conclusions regarding tree development in space and time. [ABSTRACT FROM AUTHOR]- Published
- 2005
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22. Viola rupestris: molecular analyses to elucidate postglacial migration in Western Europe.
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Nordal, Inger, Jonsell, Bengt, and Marcussen, Thomas
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ANIMAL migration ,ANIMAL behavior ,BIOGEOGRAPHY ,GEOGRAPHY - Abstract
Our aim was to elucidate the postglacial migration of Viola rupestris F.W. Schmidt, with its two subspecies, rupestris and relicta Jalas, in Europe, using molecular methods. Norway, Sweden, Finland, England, the Netherlands, France and Switzerland. Isoenzymes were analysed from 49 populations of Viola rupestris s.lat. Based on former experience of variation in the taxon, the following were included: aspartate aminotransferase, leucine/aminopeptidase, and phosphoglucomutase, yielding a total of nine interpretable and six variable (putative) loci. Six multilocus phenotypes were revealed ( A–F). Phenotype A (only one individual) is restricted to northern Norway, B is shared by all populations in northern Norway and an isolated population on the west coast of southern Norway (Møre). Phenotype B comes close to C, co-occurring with D in England, the latter also occurring in southern France. Phenotypes E and F occur in the rest of Europe. Viola rupestris ssp. relicta Jalas, previously known only from northern Scandinavia (northern unicentric), was discovered on the west coast of southern Norway (Møre), making the taxon ‘bicentric’. Populations are connected through a putative migration route from the Grands Causses in southern France (Massif Central) via England and western Norway to northern Scandinavia. The Grands Causses might represent a glacial refugium. [ABSTRACT FROM AUTHOR]
- Published
- 2005
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23. Molecular biogeography of the arctic-alpine disjunct burnet moth species Zygaena exulans (Zygaenidae, Lepidoptera) in the Pyrenees and Alps.
- Author
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Schmitt, Thomas and Hewitt, Godfrey M.
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PHYLOGEOGRAPHY ,MOTHS ,ANIMAL species ,ISOENZYMES ,ANIMAL genetics ,PLEISTOCENE stratigraphic geology - Abstract
The phylogeography of ‘southern’ species is relatively well studied in Europe. However, there are few data about ‘northern’ species, and so we studied the population genetic structure of the arctic-alpine distributed burnet moth Zygaena exulans as an exemplar. The allozymes of 209 individuals from seven populations (two from the Pyrenees, five from the Alps) were studied by electrophoresis. All 15 analysed loci were polymorphic. The mean genetic diversities were moderately high ( A: 1.99; H
e : 11.5; P: 65%). Mean genetic diversities were significantly higher in the Alps than in the Pyrenees in all cases. FST was 5.4% and FIS was 10%. Genetic distances were generally low with a mean of 0.022 between large populations. About 62% of the variance between populations was between the Alps and the Pyrenees. The two samples from the Pyrenees had no significant differentiation, whereas significant differentiation was detected between the populations from the Alps ( FST = 2.8%, P = 0.02). Zygaena exulans had a continuous distribution between the Alps and the Pyrenees during the last ice age. Most probably, the species was not present in Iberia, and the samples from the Pyrenees are derived from the southern edge of the glacial distribution area and thus became genetically impoverished. Post-glacial isolation in Alps and Pyrenees has resulted in a weak genetic differentiation between these two disjunct high mountain systems. [ABSTRACT FROM AUTHOR]- Published
- 2004
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24. Did Native Americans influence the northward migration of plants during the Holocene?
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MacDougall, Andrew
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PLANT dispersal ,NATIVE Americans ,ETHNOBOTANY ,AGRICULTURAL history - Abstract
Abstract Long-distance plant dispersal explains the rapid northward migration of plant species during the Holocene but the mechanisms by which it occurred are poorly understood. Given that Native Americans spread numerous cultigens over thousands of kilometres during the late Holocene, I examined historical literature for evidence of non-cultigen dispersal or cultivation in North America's eastern woodlands. Cultivation references are included because a strong relationship between dispersal and indigenous flora husbandry is assumed. Sixty-seven texts describing Native American lifestyle, cultural activities, and land management reported some form of plant use. Most accounts, however, focus on cultigen production or the use of indigenous flora for medicine or food without mention of dispersal. Twenty-four of the texts described the trade, transport, or cultivation of plants indigenous to eastern North American woodlands. Most accounts focus on the informal production of food plants, especially trees and shrubs. Confounding these reports was clear evidence of observer bias, limited botanical knowledge, acculturation, and secrecy by Native American informants. Because of these shortcomings, the likelihood of widespread long-distance plant dispersal by Native Americans could not be determined using historical literature. This activity was either not widespread or was not observed by, or revealed to, Europeans. To adequately test the Native American plant dispersal hypothesis, direct evidence from other sources (e.g. archaeobotancial data) will be required. [ABSTRACT FROM AUTHOR]
- Published
- 2003
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25. Holocene landscape development and human impact in the Connemara Uplands, Western Ireland.
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Huang, Chun Chang
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LANDSCAPES ,BIOGEOGRAPHY - Abstract
Aim Aim Investigate: (1) the role of human impact in shaping the landscape and particularly the initiation of blanket bog; (2) the short-lived abrupt changes and their causation; (3) the phenomenon of large-scale upland peat erosion to answer the question of when and why erosion of upland blanket peat commenced in the Connemara uplands. Location Lough Maumeen in the Maumeen Gap, Connemara, Western Ireland. Methods Pollen, sedimentary analysis and
14 C dating on the lake sediment cores. Results Pollen diagrams, charcoal fragments, bulk and dry densities, mineral content (or loss-on-ignition), whole core magnetic susceptibility, specific magnetic susceptibility for the core profile. Main conclusions Pine-dominated woodland developed from 9250 BP. Human activities effected the deforestation between 5050–4000 BP. Peat bog initiated on the wet hollow ground in the gap during the elm decline. The major expansion of blanket bog landscape in the upland commenced at 4000 BP following immediately the Taxus decline. Human impact was the dynamic force responsible for the destruction of the woodland and the formation of blanket bog in the upland. Three episodes of short-lived erosion events were identified between 8650–8400 BP, 5450–5250 BP, and 600–200 cal. BP, respectively. They are very different from each other in their causation. Large-scale peat erosion is a recent phenomenon. It has been caused by intensive sheep grazing, which has been extended to the upland blanket bogs since the late eighteen century. [ABSTRACT FROM AUTHOR]- Published
- 2002
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26. Plant migration rates and seed dispersal mechanisms.
- Author
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Pakeman
- Subjects
PLANT migration ,SEED dispersal - Abstract
Aim Holocene plant migration rates appear to greatly exceed measured dispersal distances. This is a feature of species with all dispersal mechanisms and in all communities. The role of dispersal by large mammalian herbivores is explored as a mechanism that accounts for the observed dispersal rates. Methods A simple model was constructed that took into account herbivore dispersal and how migration rates might vary with herbivore territory size, gut survival and probability of consumption. Results Even at relatively low probabilities of consumption and gut survival, dispersal by animals within large territories could account for observed rates of dispersal in the palaeorecord. Animals with small territory sizes could not produce large enough rates of dispersal. Main conclusions As many modern day grassland plants appear to survive gut passage, endozoochory by large mammalian herbivores could be the main mechanism for long-distance dispersal of herbaceous species. [ABSTRACT FROM AUTHOR]
- Published
- 2001
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27. Estimating past floristic diversity in montane regions from macrofossil assemblages.
- Author
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Allen, Judy R. M. and Huntley, Brian
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PLANT diversity ,MOUNTAINS ,FOSSILS - Abstract
SummaryThe relationship between the diversity of higher plant macrofossils in surface sediments of lakes and the surrounding vegetation is examined in two mountain regions; Grødalen in central Norway and the south-east Cairngorms in Scotland. Two lake sediment cores from each area were also analysed to examine vegetation history and to estimate changes in biodiversity through the Holocene. The diversity of present day vegetation in each region was estimated using both quadrat data and classified satellite images of the study areas. The mean surface sample macrofossil representation of species recorded in quadrats collected within 250 m of the lakes was c. 17%. This figure drops to only c. 2% when the satellite imagery of the same area is used to provide a maximal species list. The macrofossil data from the Norwegian cores show that deglaciation in this region occurred earlier on the mountain summit than in the valley and that the maximum tree line elevation was during the interval 9100–4400
14 C yr BP. In the Cairngorms the maximum tree line elevation was prior to c. 450014 C yr BP. The changes in higher plant diversity recorded at these sites through the Holocene show that c. 400014 C yr BP the reduction in the tree line resulted in decreased β-diversity at higher altitudes but an increase at the lower altitude as the forest cover opened up. Under conditions of climatic warming it is likely areas that come to lie below the tree line will experience reduced diversity and that a permanent loss of biodiversity would result from a severe reduction in the area above the tree line. [ABSTRACT FROM AUTHOR]- Published
- 1999
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28. Long-term effects of human impact on mountainous ecosystems, western Taurus Mountains, Turkey
- Author
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V. De Laet, Etienne Paulissen, David Kaniewski, Marc Waelkens, Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Center for Archaeological Sciences, Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), and Physical and Regional Geography Research Group
- Subjects
2. Zero hunger ,010506 paleontology ,010504 meteorology & atmospheric sciences ,Ecology ,Biogeography ,Vegetation ,Land cover ,15. Life on land ,Structural basin ,Spatial distribution ,01 natural sciences ,Geography ,13. Climate action ,Ecosystem ,Physical geography ,Transect ,ComputingMilieux_MISCELLANEOUS ,Ecology, Evolution, Behavior and Systematics ,Holocene ,0105 earth and related environmental sciences - Abstract
Aim To investigate the human impact on eastern Mediterranean ecosystems in a subhumid to semi-arid region of the Near East. Location This paper considers data from Bereket (1410-1440 m a.s.l.), an intramontane basin surrounded by the Kokayamk Tepe (1830 m a.s.l.) and the Besparmak Daglari (2280 m a.s.l.), in the western Taurus Mountains of south-west Turkey. Methods Late Holocene samples were collected along an 800-cm-deep sediment profile cored in the secondary valley of the Bereket basin. Descriptive vegetation data and modern pollen samples (moss polsters) were collected at elevational intervals of c. 15 m along an altitudinal transect from the Bereket basin (over Tepe Duzen, 1600 m a.s.l.) to Aglasun Dagi (1700 m a.s.l.). Information about the spatial distribution of the present land cover was obtained from ASTER satellite imagery. Digital elevation-derived data and geological information were used to examine the relationship between actual land cover and other environmental variables. Results The well dated Bereket sequence provides a unique record of biennial-to-decadal landscape changes driven primarily by intensive human impact from 360 cal. yr BC to 650 cal. yr AD. Since 360 cal. yr BC, over-exploitation of the land has led to altitudinal variation of tree lines, a destruction of the natural forest ecosystems (Pinus-Quercus cerris mixed forest), and an extensive spread of forest-steppe in the highlands. The present-day distribution of vegetation in the basin area shows that human activities remain the major factor influencing the character of modern ecosystems. Main conclusions This research demonstrates the long-term local destructive effects of human impacts on the mountainous ecosystems in a small Anatolian intramontane basin since 360 cal. yr BC, and the capacity of these ecosystems to recover during periods of reduced human impact. The late Holocene history and modern vegetation characteristics show that the past and present-day distribution and composition of vegetation are influenced primarily by human activity, and that substrate, elevation, slope and orientation are of secondary significance.
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- 2007
29. Holocene global warming and the origin of the Neotropical Gran Sabana in the Venezuelan Guayana
- Author
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Valentí Rull
- Subjects
Cloud forest ,Neotropics ,Peat ,Holocene ,Ecology ,Pleistocene ,Global warming ,Climate change ,Global change ,Vegetation ,Fires ,Palaeoclimates ,Geography ,Long-term ,Charcoal ,Savanna ,Pollen ,Forest–savanna mosaics ,Glacial period ,Ecology, Evolution, Behavior and Systematics - Abstract
10 p., [EN] Aim The assumedly anomalous occurrence of savannas and forest–savanna mosaics in the Gran Sabana – a neotropical region under a climate more suitable for tropical rain forests – has been attributed to a variety of historical, climatic, and anthropogenic factors. This paper describes a previously undocumented shift in vegetation and climate that occurred during the early Holocene, and evaluates its significance for the understanding of the origin of the Gran Sabana vegetation. Location A treeless savanna locality of the Gran Sabana (4 30¢–6 45¢ N and 60 34¢–62 50¢ W), in the Venezuelan Guayana of northern South America, at the headwaters of the Caronı´ river, one of the major tributaries of the Orinoco river. Methods Pollen and charcoal analysis of a previously dated peat section spanning from about the Pleistocene/Holocene boundary until the present. Results Mesothermic cloud forests dominated by Catostemma (Bombacaceae) occupied the site around the Pleistocene/Holocene boundary. During the early Holocene, a progressive but relatively rapid trend towards savanna vegetation occurred, and eventually the former cloud forests were replaced by a treeless savanna. Some time after the establishment of savannas, a marked increase in charcoal particles indicates the occurrence of the first local fires. Main conclusions The occurrence of cloud forests at the Pleistocene/Holocene boundary contradicts the historical hypothesis according to which the Gran Sabana is a relict of the hypothetical widespread savannas that have been assumed to have dominated the region during the last glaciation. The first local fires recorded in the Holocene were on savanna vegetation, which is against the hypothesis of fire as the triggering factor for the establishment of these savannas. Climate change, in the form of global warming and a persistently drier climate, emerges as the most probable cause for the forest–savanna turnover.
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- 2007
30. A brief history of Great Basin pikas
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Donald K. Grayson
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education.field_of_study ,American pika ,Ecology ,biology ,Biogeography ,Population ,Climate change ,Context (language use) ,biology.organism_classification ,humanities ,law.invention ,Geography ,law ,Radiocarbon dating ,Pika ,education ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Aim Within the past few decades, seven of the 25 historically described populations of American pikas (Ochotona princeps) in the Great Basin of arid western North America appear to have become extinct. In this paper, the prehistoric record for pikas in the Great Basin is used to place these losses in deeper historical context. Location The Great Basin, or area of internal drainage, of the western United States. Methods The location, elevation, and age of all reported prehistoric Great Basin specimens of American pikas were extracted from the literature. Elevations of extinct pika populations were arrayed through time, and latitudes and longitudes of those populations used to determine changing distances of those populations from the nearest extant populations. Results The average elevation of now-extinct Great Basin pika populations during the late Wisconsinan (c. 40,000–10,000 radiocarbon years ago) and early Holocene (c. 10,000–7500 years ago) was 1750 m. During the hot and dry middle Holocene (c. 7500–4500 years ago), the average elevation of these populations rose 435 m, to 2168 m. All prehistorically known late Holocene (c. 4500–200 years ago) populations in the Great Basin are from mountain ranges that currently support populations of this animal, but historic period losses have caused the average elevation of pika populations to rise an additional 152 m. The total elevational increase, from the late Wisconsinan and early Holocene to today, has been 783 m. As lower elevation pika populations were lost, their distribution increasingly came to resemble its modern form. During the late Wisconsinan, now-extinct pika populations were located an average of 170 km from the nearest extant population. By the late Holocene, this distance had declined to 30 km. Main conclusions Prehistoric alterations in the distribution of pika population in the Great Basin were driven by climate change and attendant impacts on vegetation. Today, Great Basin pikas contend with both climate change and anthropogenic impacts and thus may be on the brink of extinction.
- Published
- 2005
31. The Holocene spread of Picea abies (L.) Karst. in Fennoscandia and adjacent areas
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Keith Bennett and Thomas Giesecke
- Subjects
education.field_of_study ,geography.geographical_feature_category ,Ecology ,biology ,Biogeography ,location.country ,Population ,Macrofossil ,Picea abies ,medicine.disease_cause ,biology.organism_classification ,Karst ,location ,Geography ,Byelorussia ,Pollen ,medicine ,Physical geography ,education ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Aim The Holocene spread of Picea abies in Fennoscandia is well established from many sites and thus provides an opportunity for detailed study of the dynamics of tree spread and population expansion. Early- and mid-Holocene macrofossil evidence for presence of P. abies in Fennoscandia has questioned traditional interpretations of the timing and direction of its spread. This paper aims to determine when, from where and by which pathways P. abies spread into Fennoscandia. Understanding the character and dynamics of this spread may give insight into the general understanding of Holocene tree spread. Location The north-western distribution of P. abies in Europe, including Norway, Sweden, Finland, Estonia, Latvia, Lithuania, north-western Russia, parts of Byelorussia and Poland. Methods Holocene pollen diagrams with independent dating control were collected from this region. The timing of the onset of the continuous curve, the timing of the rise of the curve, the first appearance of frequencies of 1%, 3%, 5%, and 10%, as well as timing and the maximum amount of P. abies pollen, was obtained from these pollen diagrams. A GIS analysis was used to display the data and interpolate ages over the area under investigation. Results Maps are presented showing a clear ESE to WNW trend in the spread of P. abies for all characters interpolated. The timing of the rise of the curve was difficult to use as sites east of the Baltic have slowly rising P. abies frequencies while the western sites often show a rapid rise. Main conclusions The spread of P. abies in Fennoscandia and adjacent areas can be separated into two phases: (i) A rapid early Holocene spread out of Byelorussia and northern Russia at low population density giving rise to small outpost populations, possibly as far west as the Scandes Mountains. (ii) A mid- to late Holocene front-like spread at high population densities moving from east to west into the Baltic Republics and Finland, into northern Scandinavia and then moving south and west towards its present-day distributional limits.
- Published
- 2004
32. Boreal tree taxa in the central Scandes during the Late-Glacial: implications for Late-Quaternary forest history
- Author
-
Leif Kullman
- Subjects
geography ,geography.geographical_feature_category ,Ecology ,biology ,Picea abies ,biology.organism_classification ,Boreal ,Deglaciation ,Stadial ,Glacial period ,Physical geography ,Younger Dryas ,Ice sheet ,Ecology, Evolution, Behavior and Systematics ,Geology ,Holocene - Abstract
Aim This paper seeks to elucidate the first post-glacial arrival of tree species to high elevations in the Scandes. This enables testing of general theories concerning glacial refugia, immigration routes and palaeoclimate. Location The study site, 1360 m a.s.l., was close to the summit of Mt Areskutan in the alpine region of the southern Swedish Scandes, 400–500 m above modern tree-limits. Methods Tree megafossils (trunks, roots, cones) were retrieved (and radiocarbon-dated) from the ground surface in the forefields of receding `perennial' snow-patches. This approach allows elevational range-margin reconstructions to be made with an accuracy not possible with any other method. Results and conclusions Megafossils were recovered substantially higher and earlier than previously recorded or inferred for tree growth in this part of Europe. The species were Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman, Picea abies (L.) Karst. and Pinus sylvestris (L.). The oldest dates obtained are c. 14,000, 11,000 and 11,700 BP for these species, respectively. For the first time, explicit evidence of tree growth in the Late-Glacial (including the Younger Dryas stadial) is demonstrated for central/northern Scandinavia. The swift appearance of boreal tree species at high northern latitudes and altitudes on the western fringe of Scandinavia and near the most extended margin of the Weichselian ice sheet hypothetically suggests that the first immigration of the trees considered here was from the west. Glacial refugia for these species (other plants and animals as well) on the exposed continental shelf areas west and southwest of Norway is hypothesized. By extension, the results fit into a more general pattern, suggesting the presence of boreal and temperate trees quite close to the full glacial (Weichselian) ice margins in central Europe. Thus, the Quaternary forest and landscape history of Europe seems more complex than previously believed.
- Published
- 2002
33. Continuity or discontinuity? Vegetation change in the Hadrianic-Antonine frontier zone of northern Britain at the end of the Roman occupation
- Author
-
Lisa Dumayne-Peaty
- Subjects
Palynology ,geography ,geography.geographical_feature_category ,Peat ,Ecology ,biology ,Fell ,Woodland ,biology.organism_classification ,Archaeology ,Moss ,law.invention ,law ,Radiocarbon dating ,Bog ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Summary Aim The aim of this paper is to determine the nature of vegetation change in the Hadrianic-Antonine frontier zone of northern Britain at the end of the Roman occupation. The concepts of continuity and change are important issues in palynological and archaeological studies and it has been assumed traditionally that large-scale woodland regeneration occurred in the area at the end of the Romano-British period. Location Hadrianic–Antonine frontier zone of northern Britain. Methods Pollen analysis of peat profiles, radiocarbon dating Results and main conclusions The pollen diagrams suggest that woodland regeneration occurred around the time of the withdrawal of Roman troops at Fozy Moss, Northumbria; Glasson Moss, Cumbria; Bolton Fell Moss (marg), Cumbria; Letham Moss, Stirlingshire; Cranley Moss, Lanarkshire; Carsegowan Moss, Wigtonshire and Dogden Moss, Berwickshire. Regeneration started at Blairbech Bog, Dumbartonshire and Ellergower Moss, Dumfriesshire before the Roman occupation began. The landscape around Walton Moss, Cumbria remained open later and regeneration of woodland did not take place until the latter half of the sixth century AD. Woodland regeneration at each of the sites was also associated with a decline in agricultural production, and renewed clearance did not occur until Anglian, monastic or Scandinavian settlement took place.
- Published
- 1999
34. Fossil wood charcoal assemblages from Elands Bay Cave, South Africa: implications for Late Quaternary vegetation and climates in the winter-rainfall fynbos biome
- Author
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Richard M. Cowling, J. C. Allsopp, John Parkington, and Caroline R. Cartwright
- Subjects
Ecology ,Biome ,Vegetation ,Deserts and xeric shrublands ,Geography ,visual_art ,visual_art.visual_art_medium ,Fossil wood ,Glacial period ,Charcoal ,Quaternary ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Summary Aim The aim of this paper is to analyse fossil charcoal deposits, largely identified to the species level and spanning a sequence from the late Holocene to < 40,000 BP, in order to reconstruct Late Quaternary vegetation and climatic patterns in the western (winter-rainfall) fynbos biome of South Africa. Location The charcoals were excavated from the Elands Bay Cave (32°19S, 18°20E) on the semiarid (200–250 mmyr−1), winter-rainfall coastline of the western fynbos biome. Methods Patterns in the charcoal data set over time were sought by manual sorting of the charcoal×sample matrix, as well as by subjecting the data to multivariate analysis. Palaeoclimatic reconstruction was attempted by comparing the climatic controls on contemporary vegetation communities that resembled the fossil assemblages. Charcoal diversity was modelled using sample age and number of charcoal fragments as explanatory variables. Results The fossil assemblages ranged from xeric communities (similar to those presently occurring at the site) during the Holocene, to more mesic thicket and fynbos vegetation in the terminal Pleistocene, to Afromontane forest and riverine woodland communities after about 18,000 BP. Diversity of the charcoal samples increased monotonically with increasing sample age. Main conclusions The results suggest that, unlike the eastern fynbos biome, which is under fundamentally different climatic controls, soil moisture conditions in the western part of the biome were higher in the Last Glacial than during the Holocene. This scenario may help to explain the higher regional richness and associated diversification in the western than eastern part of the biome.
- Published
- 1999
35. Evidence for drought and forest declines during the recent megafaunal extinctions in Madagascar
- Author
-
Lindsey Gillson, Malika Virah-Sawmy, and Katherine J. Willis
- Subjects
Geography ,Ecology ,Environmental change ,Megafauna ,Littoral zone ,Paleoecology ,Climate change ,Woodland ,Fire ecology ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Aim There remains some uncertainty concerning the causes of extinctions of Madagascar's megafauna. One hypothesis is that they were caused by over-hunting by humans. A second hypothesis is that their extinction was caused by both environmental change and hunting. This paper systematically addresses the second hypothesis through examination of two new pollen records from south-eastern Madagascar alongside other published records across the island. Location South-eastern Madagascar. Methods We reconstructed past vegetation and fire dynamics over the past 6000 years at two sites in south-eastern Madagascar (Ste-Luce) using fossil pollen and charcoal contained in sedimentary sequences. We investigated drivers of vegetation changes and how these, in turn, influenced faunal species in the south-east, using published climatic, archaeological and faunal records. Further, we also used published records to provide a synthesis of environmental changes on the whole island. Results Vegetation reconstructions indicate that the mosaic vegetation in the region of Ste-Luce was highly dynamic in response to climatic changes. The open woodland, surrounding the littoral forest, transformed into an ericoid grassland between c. 5800 and 5200 cal. yr bp, possibly in response to a moderate drought recorded during this period. The littoral forest was more stable between c. 5100 and 1000 cal. yr bp, with only some minor compositional changes c. 2800 cal. yr bp and between c. 1900 and 1000 cal. yr bp. Significant forest decline, however, is observed at c. 950 cal. yr bp, coinciding with a drought and a marine surge. A comparison of these results with a synthesis of published vegetation records across the island shows asynchronous vegetation changes in response to various droughts during the Holocene, except for the 950 cal. yr bp drought event, with evidence of widespread vegetation transformations and fires across the island. Main conclusions Pronounced climatic desiccation between 1200 and 700 cal. yr bp may have been the slow driver framing and triggering vegetation transformations and decline in megafaunal populations. In addition, hunting by drought-impacted human inhabitants and competition with newly introduced cattle would have amplified the impacts on megafaunal populations, leading to numerous extinctions in this period. © 2009 Blackwell Publishing Ltd.
- Published
- 2010
36. Vegetation and fire history of a Chinese site in southern tropical Xishuangbanna derived from phytolith and charcoal records from Holocene sediments
- Author
-
Shucheng Xie, Yansheng Gu, Deborah M. Pearsall, and Jianxin Yu
- Subjects
Ecology ,Global warming ,Climate change ,Vegetation ,Rainforest ,Geography ,Phytolith ,visual_art ,visual_art.visual_art_medium ,Aridity index ,Charcoal ,Ecology, Evolution, Behavior and Systematics ,Holocene - Abstract
Aim The aims of this paper are to reconstruct the vegetation and fire history over the past 2000 years in a well-preserved rain-forest area, to understand interactions between climate, fire, and vegetation, and to predict how rain forest responds to global warming and increased intensity of human activity. Location Xishuangbanna, south-west China, 21–22° N, 101–102° E. Methods Phytolith (plant opal silica bodies) morphotypes, assemblages, and indices were used to reconstruct palaeovegetation and palaeoclimate changes in detail. Micro-charcoal particles found in phytolith slides, together with burnt phytoliths and highly weathered bulliform cells, were employed to reconstruct a record of past fire occurrence. A survey of field sediments, lithology, and 14C dating were also employed. Results Phytoliths were divided into 11 groups and classified into 33 well-described morphotypes according to their shape under light microscopy and their presumed anatomical origins and ecological significance. The phytolith assemblages were divided into six significant zones that reveal a complete history of vegetation changes corresponding to climate variation and fire occurrence. Phytolith assemblages and indices show that the palaeoclimate in the study area is characterized by the alternation of warm–wet and cool–dry conditions. Phytolith and charcoal records reveal that 12 fire episodes occurred. Comparison of burnt phytoliths with an aridity index (Iph) shows that fire episodes have a strong relationship with drought events. Main conclusions Our results indicate that fire occurrence in the tropical rain forest of Xishuangbanna is predominantly under the control of natural climate variability (drought events). Nearly every fire episode is coupled with a climatic event and has triggered vegetation composition changes marked by a pronounced expansion of grasses. This indicates that drought interacts with fire to exert a strong influence on the ecological dynamics of the rain forest. However, the impact of human activity in recent centuries is also significant. Our results are important for understanding the interactions between climate, fire, and vegetation, and for predicting how rain forest responds to global warming and increased human activity.
- Published
- 2007
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