| 1. |
- Fontana, Sonia L., et al.
(författare)
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Palaeoenvironmental changes since the Last Glacial Maximum : Patterns, timing and dynamics throughout South America
- 2012
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 22:11, s. 1203-1206
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The vast diversity of present vegetation and environments that occur throughout South America (12 degrees N to 56 degrees S) is the result of diverse processes that have been operating and interacting at different spatial and temporal scales. Global factors, such as the concentration of CO2 in the atmosphere, may have been significant for high altitude vegetation during times of lower abundance, while lower sea levels of glacial stages potentially opened areas of continental shelf for colonisation during a substantial portion of the Quaternary. Latitudinal variation in orbital forcing has operated on a regional scale. The pace of climate change in the tropics is dominated by precessional oscillations of c. 20 kyr, while the high latitudes of the south are dominated by obliquity oscillations of c. 40 kyr. In particular, seasonal insolation changes forced by precessional oscillations must have had important consequences for the distribution limits of species, with potentially different effects depending on the latitude. The availability of taxa, altitude and human impact, among other events, have locally influenced the environments. Disentangling the different forcing factors of environmental change that operate on different timescales, and understanding the underlying mechanisms leads to considerable challenges for palaeoecologists. The papers in this Special Issue present a selection of palaeoecological studies throughout South America on vegetation changes and other aspects of the environment, providing a window on the possible complexity of the nature of transitions and timings that are potentially available.
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| 2. |
- Parducci, Laura, et al.
(författare)
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Glacial Survival of Boreal Trees in Northern Scandinavia
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 335:6072, s. 1083-1086
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Tidskriftsartikel (refereegranskat)abstract
- It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandinavia and with its highest frequency to the west-an area believed to sustain ice-free refugia during most of the last ice age. We further show the survival of DNA from this haplotype in lake sediments and pollen of Trondelag in central Norway dating back similar to 10,300 years and chloroplast DNA of pine and spruce in lake sediments adjacent to the ice-free Andoya refugium in northwestern Norway as early as similar to 22,000 and 17,700 years ago, respectively. Our findings imply that conifer trees survived in ice-free refugia of Scandinavia during the last glaciation, challenging current views on survival and spread of trees as a response to climate changes.
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| 3. |
- Parducci, Laura, et al.
(författare)
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Molecular- and pollen-based vegetation analysis in lake sediments from central Scandinavia
- 2013
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 22:13, s. 3511-3524
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Tidskriftsartikel (refereegranskat)abstract
- Plant and animal biodiversity can be studied by obtaining DNA directly from the environment. This new approach in combination with the use of generic barcoding primers (metabarcoding) has been suggested as complementary or alternative to traditional biodiversity monitoring in ancient soil sediments. However, the extent to which metabarcoding truly reflects plant composition remains unclear, as does its power to identify species with no pollen or macrofossil evidence. Here, we compared pollen-based and metabarcoding approaches to explore the Holocene plant composition around two lakes in central Scandinavia. At one site, we also compared barcoding results with those obtained in earlier studies with species-specific primers. The pollen analyses revealed a larger number of taxa (46), of which the majority (78%) was not identified by metabarcoding. The metabarcoding identified 14 taxa (MTUs), but allowed identification to a lower taxonomical level. The combined analyses identified 52 taxa. The barcoding primers may favour amplification of certain taxa, as they did not detect taxa previously identified with species-specific primers. Taphonomy and selectiveness of the primers are likely the major factors influencing these results. We conclude that metabarcoding from lake sediments provides a complementary, but not an alternative, tool to pollen analysis for investigating past flora. In the absence of other fossil evidence, metabarcoding gives a local and important signal from the vegetation, but the resulting assemblages show limited capacity to detect all taxa, regardless of their abundance around the lake. We suggest that metabarcoding is followed by pollen analysis and the use of species-specific primers to provide the most comprehensive signal from the environment.
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| 4. |
- Parducci, Laura, et al.
(författare)
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Response to Comment on "Glacial Survival of Boreal Trees in Northern Scandinavia"
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 338:6108, s. 742-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Birks et al. question our proposition that trees survived the Last Glacial Maximum (LGM) in Northern Scandinavia. We dispute their interpretation of our modern genetic data but agree that more work is required. Our field and laboratory procedures were robust; contamination is an unlikely explanation of our results. Their description of Endletvatn as ice-covered and inundated during the LGM is inconsistent with recent geological literature.
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| 5. |
- Stutz, Silvina, et al.
(författare)
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Late Holocene climate and environment of the SE Pampa grasslands, Argentina, inferred from biological indicators in shallow, freshwater Lake Nahuel Rucá
- 2010
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:3, s. 761-775
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed pollen, non-pollen palynomorphs (NPPs), calcareous microfossils, plant macrofossils, diatoms, chrysophyte cysts, opal phytoliths and organic matter content in a 123-cm sediment sequence from Nahuel Ruca Lake, a shallow, freshwater system in the southeastern Pampa grasslands, Argentina. Three stages in the lake evolution were identified. Before 3,680 cal year BP, only pollen, NPPs (dinoflagellate cysts and acritarchs) and ostracods were recovered, suggesting brackish/saline conditions in the lake and nearby areas. Freshwater conditions are, however, indicated by Myriophyllum, Pediastrum and Zygnemataceae. The brackish/saline conditions could have been caused by marine influence during a Holocene sea level high stand that affected the area ca. 6,000 year BP. Between 3,680 and 390 cal year BP, macrophyte pollen and plant macrofossils indicate increasingly freshwater conditions in the lake and the adjacent area. Diatom and ostracod assemblages, however, suggest brackish and oligotrophic conditions, giving way to freshwater and meso-eutrophic conditions toward the end of this period. The relationship between submersed macrophytes (Myriophyllum, Potamogeton, Ceratophyllum, Chara) and planktonic algae (Chlorophyta and diatoms), suggests a shift in the lake from a clear to a turbid state. This turbid state is more evident after 390 cal year BP. High values of Pediastrum, Scenedesmus and diatoms (Cyclotella meneghiniana, Aulacoseira granulata, A. muzzanensis) observed during this stage could have reduced light penetration, with consequent loss of submersed plants. Pollen and plant macrofossils in the uppermost 20 cm indicate a shallow, freshwater lake similar to present, though an increase in brackish/freshwater diatoms suggests an increase in salinity, perhaps related to periodic droughts. Opal phytoliths yield a regional paleoclimatic reconstruction that agrees closely with inferences made using pollen, mammals and sediment characteristics.
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