| 1. |
- Cui, Qiao-Yu
(författare)
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Fire history in the hemiboreal and southern boreal zones of southern Sweden during 11000 years : Relationships with past vegetation composition and human activities and implications for biodiversity issues
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies fire history over the last 11 000 years (Holocene) in central Småland, southern Sweden, on the basis of palaeoecological analyses of peat sequences from three small bogs (Notteryd, Stavsåkra and Storasjö). The main objective is to gain insights into the long-term relationships between fire, climate, human-impact, other environmental factors and the history of biodiversity in the study region. The following hypotheses are tested: 1) there are no between-site differences in i) Holocene fire history, ii) abundance of deciduous trees versus pine and forest openness over the Holocene, and iii) landscape history over the last three centuries, and 2) there are no within-site differences in the Holocene charcoal records.Hypothesis 1 (i-iii) is tested using all charcoal records (three sites) and pollen-based Landscape Reconstruction Algorithm (LRA) estimates of past percentage cover of plant taxa and land-use/vegetation units over the last three centuries (test of the LRA using historical maps), and the entire Holocene. Hypothesis 2 is tested using two parallel charcoal records from the same core at Notteryd. The charcoal data comprise continuous records of macroscopic charcoal (macro-C), microscopic charcoal records from pollen slides, and identification of charcoal fragments to plant taxa. Chronologies are based on series of 14C dates from terrestrial plant remains and age-depth models achieved using Bayesian statistics.Accumulation rates (AR) of the area of macro-C was found to be better to use than AR of the number of macro-C for interpretation of the results. Within-site differences in charcoal records exist and have to be considered. Besides climate, forest tree-composition (related to geomorphological settings) was shown to play a primordial role in Early and Mid-Holocene fire history, while land-use was a major factor in the Late Holocene. Three different histories of forest development and land-use changes within the same region are revealed, implying a multitude of landscape types over time and space. These long-term landscape histories were at the origin of the high biodiversity still existing in the 18th century. Major landscape transformations due to agrarian reforms since the 18th century resulted in a dramatic loss of landscape and species biodiversity over the last two centuries.
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| 2. |
- Fontana, Sonia L., 1969-
(författare)
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Present and Past Coastal Dune Environments of South Buenos Aires Province, Argentina
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to describe present and past coastal dune environments in southern Buenos Aires Province, Argentina. The present vegetation of a dune system and its zonation are described on the basis of air photographs, physiognomy of the dune system and floristic composition. The vegetation was characterized by a large number of Poaceae and Asteraceae species. Five vegetation zones, based on floristic composition, were defined by cluster analysis. Pollen-vegetation comparison revealed that pollen assemblages differed considerably from the associated vegetation. Some of the major discrepancies were caused by large differences between pollen and vegetation proportion of Hyalis argentea and Discaria americana. However, the local vegetation was well represented in recent soil samples. Pollen traps recorded predominantly extralocal and regional pollen. A new species of ostracods was recovered from an interdunal lake. The species, a giant cypridid, was described and illustrated, and its geographical distribution and ecology were discussed. Two sediment sequences from the coastal intertidal zone and from a shallow freshwater lake were analysed for loss on ignition, calcareous microfossils (ostracods and foraminifers), macro remains and pollen. The coastal sequence was deposited between 7890 and 7630 cal. BP. Its pollen assemblages were typical for halophytic associations, with some psammophytic taxa also present in recent vegetation. The microfossils were representative of a littoral lagoon. The lake sequence comprised the last 3000 cal. BP. Pollen spectra indicated a relatively stable vegetation composition after the lake had been formed. Pollen assemblages reflected the present regional grassland vegetation with taxa characteristic for the surrounding dune communities. Human settlement was indicated in the pollen spectra by the presence of introduced taxa in the uppermost samples. The data presented provide a useful reference for the interpretation of fossil sequences from similar environments.
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| 3. |
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| 4. |
- Li, Furong, 1986-
(författare)
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Pollen productivity estimates and pollen-based reconstructions of Holocene vegetation cover in Northern and temperate China for climate modelling
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Model projections of future climate change require that coupled climate-vegetation models are developed and validated, i.e. these models should be able to reproduce past climate and vegetation change. Records of pollen deposited in lake bottoms and peat bogs can provide the information needed to validate these models. The aim of this thesis was i) to explore the modern relationships between pollen and vegetation in northern and temperate China and estimate pollen productivity of major plant taxa, and ii) to use the results of i) to produce the first reconstruction of plant cover in China over the last 10 000 years for the purpose of climate modelling. A study of the modern pollen-vegetation-climate relationships was performed in northwestern China (Paper I). Pollen productivity for 18 major plants of cultural landscapes in central-eastern China was estimated (Paper II). Based on a synthesis and evaluation of all existing estimates of pollen productivity in the study region, a standard dataset of pollen productivity for 31 plant taxa is proposed (Paper III). This dataset was used to achieve pollen-based REVEALS reconstructions of plant cover over the last 10 000 years in 35 regions of northern and temperate China (Paper IV). The major findings can be summarized as follows. Paper I: Annual precipitation (Pann) is the major climatic factor influencing pollen assemblages, followed by July precipitation (PJul). The shared effect of combinations of two climatic factors explains a larger portion of the variation in pollen data than individual variables. Paper II: Of the 16 reliable pollen productivities estimated, the estimates for 8 taxa are new, Castanea, Cupressaceae, Robinia/Sophora, Anthemis type/Aster type, Cannabis/Humulus, Caryophyllaceae, Cruciferae, and Galium type. Trees have in general larger pollen productivity than herbs. Paper III: Of the total 31 taxa for which estimates of pollen productivity are available in China, 13 taxa have more than 1 value. All or most of these values are similar for Artemisia, Cyperaceae, Larix, Quercus and Pinus. Eight taxa have very variable estimates. Paper IV: The REVEALS plant percentage-cover strongly differs from the pollen percentages, and they provide new important insights on past changes in plant composition and vegetation dynamics.
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| 5. |
- Trondman, Anna-Kari, 1980-
(författare)
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Pollen-based quantitative reconstruction of land-cover change in Europe from 11,500 years ago until present - A dataset suitable for climate modelling
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The major objective of this thesis was to produce descriptions of the land vegetation-cover in Europe for selected time windows of the Holocene (6000, 3000, 500, 200, and 50 calendar years before present (BP=1950)) that can be used in climate modelling. Land vegetation is part of the climate system; its changes influence climate through biogeophysical and biogeochemical processes. Land use such as deforestation is one of the external forcings of climate change. Reliable descriptions of vegetation cover in the past are needed to study land cover-climate interactions and understand the possible effects of present and future land-use changes on future climate.We tested and applied the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) model to estimate past vegetation in percentage cover over Europe using pollen records from lake sediments and peat bogs. The model corrects for the biases of pollen data due to intraspecific differences in pollen productivity and pollen dispersion and deposition in lakes and bogs. For the land-cover reconstructions in Europe and the Baltic Sea catchment we used 636 (grouped by 1˚x1˚ grid cells) and 339 (grouped by biogeographical regions) pollen records, respectively. The REVEALS reconstructions were performed for 25 tree, shrub and herb taxa. The grid-based REVEALS reconstructions were then interpolated using a set of statistical spatial models.We show that the choice of input parameters for the REVEALS application does not affect the ranking of the REVEALS estimates significantly, except when entomophilous taxa are included. We demonstrate that pollen data from multiple small sites provide REVEALS estimates that are comparable to those obtained with pollen data from large lakes, however with larger error estimates. The distance between the small sites does not influence the results significantly as long as the sites are at a sufficient distance from vegetation zone boundaries. The REVEALS estimates of open land for Europe and the Baltic Sea catchment indicate that the degree of landscape openness during the Holocene was significantly higher than previously interpreted from pollen percentages. The relationship between Pinus and Picea and between evergreen and summer-green taxa may also differ strongly whether it is based on REVEALS percentage cover or pollen percentages. These results provide entirely new insights on Holocene vegetation history and help understanding questions related to resource management by humans and biodiversity in the past. The statistical spatial models provide for the first time pollen-based descriptions of past land cover that can be used in climate modelling and studies of land cover-climate interactions in the past.
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