| 1. |
- Sun, Yuanhao, et al.
(författare)
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Pollen-based reconstruction of total land-cover change over the Holocene in the temperate steppe region of China : An attempt to quantify the cover of vegetation and bare ground in the past using a novel approach
- 2022
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Ingår i: Catena (Cremlingen. Print). - : Elsevier. - 0341-8162 .- 1872-6887. ; 214
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Tidskriftsartikel (refereegranskat)abstract
- Fossil pollen data are essential for reconstructing ancient vegetation and land-cover changes. Sugita's REVEALS model is the best method to estimate regional plant cover (in percentage cover) using pollen data from lakes. Such reconstructions imply that the sum of all plants' cover is 100%. However, land cover is not always represented by vegetation alone, the area of bare ground can be significant in many types of biomes, e.g., in alpine or steppe regions. Here we define "total land cover " as the sum of vegetation cover (VegC) and bare ground (BareC). In this study, we use the relationship between tree pollen percentages and both tree cover (TreeC) and VegC (=TreeC + herb cover (HerbC)) based on a dataset of modern pollen assemblages and related total land cover. This relationship is applied to estimate past "actual " vegetation cover (a-VegC) from fossil pollen percentages using the Modern Analogue Technique (MAT). The REVEALS (RV) model can then be applied to the same fossil pollen records to estimate regional cover of individual plant taxa (RV PlantC; e.g., RV PinusC, etc.), total tree cover (RV-TreeC) and total herb cover (RV-HerbC). These cover values can then be converted into RV aPlantC, RV a-TreeC and RV a-HerbC using the MAT-reconstructed a-VegC (e.g., RV PinusC x MAT a-VegC = RV aPinusC; RV-TreeC x MAT a-VegC = RV a-TreeC, etc.). The results of leave-one-out cross-validation indicates that the MAT reconstructions using the modern pollen assemblages provide values of a-TreeC, a-HerbC and BareC mostly very similar to the modern vegetation data. We further tested the method using pollen assemblages from lake surface sediments of 11 lakes and the results also suggest a good performance of MAT-based reconstruction. We then applied the proposed method (MAT-REVEALS) to four Holocene pollen records available from the study area to evaluate the feasibility of the strategy to reconstruct past actual plant cover. The results suggest that the method provides plausible estimates of vegetation cover for the sub-regions within the study area. The results from Lake Daihai over the last 10,000 years BP are interpreted and discussed in more details to evaluate the effects of possible departures from the approach assumptions.
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| 2. |
- Li, Jianyong, et al.
(författare)
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Modern pollen and land-use relationships in the Taihang mountains, Hebei province, northern China-a first step towards quantitative reconstruction of human-induced land cover changes
- 2013
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 22:6, s. 463-477
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Tidskriftsartikel (refereegranskat)abstract
- Studies of the modern relationship between pollen, vegetation and land-use are essential to infer past human impact on vegetation from pollen records. Nevertheless, such investigations are relatively few in China. We present here a study of pollen assemblages from sediment samples collected from irrigation pools in the Tuoliang and Qipanshan catchments in northern China. Pollen and spores from natural vegetation such as Artemisia, Chenopodiaceae, Pinus and Selaginella sinensis dominate the pollen assemblages, while pollen types which could be from crops such as cereals, Brassicaceae, Fabaceae, Solanaceae, Apiaceae and Cucurbitaceae are common but not abundant. Pollen percentages of Artemisia and Chenopodiaceae become less with decreasing altitude, while Pinus and S. sinensis percentages increase, indicating that saccate Pinus pollen and S. sinensis spores are transported further than non-saccate Artemisia and Chenopodiaceae pollen, and differential sorting of pollen is occurring during transport in river water. Proportions of pollen from farmland and crops increase with decreasing altitude, showing that pollen percentages of crops might be a good indicator of the extent of farmland. A linear correlation analysis between pollen percentages and vegetation proportions shows that pollen percentages of crops are positively correlated with proportions of farmland, while correlation between pollen percentages of trees, shrubs and herbs and proportions of woodland, scrubland and grassland respectively is poor. This study indicates that the relationship between pollen percentages and vegetation proportions can be explained by the differences of pollen productivity, dispersal and deposition, and might be the basis for a modelling approach to infer past vegetation cover in northern China.
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| 3. |
- Zhang, Shengrui, et al.
(författare)
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Pollen assemblages and their environmental implications in the Qaidam Basin, NW China
- 2012
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 41:4, s. 602-613
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Tidskriftsartikel (refereegranskat)abstract
- The Qaidam Basin is one of the most sensitive areas to climate change in China, owing to its unique geographical position and ecological condition. In this study, 32 surface-soil pollen samples were collected to reveal the relationship between modern pollen assemblages, vegetation and precipitation in the eastern region of the Qaidam Basin. The results show that Chenopodiaceae (3.887%, average 48%), Artemisia (1.764.2%, average 17.5%) and Ephedra (090%, average 16.3%) are the dominant pollen types in all samples, and that different pollen assemblages correspond to different vegetation types. DCA and CCA of major pollen types demonstrate that precipitation is an important factor in the control of the distribution of vegetation in the study area. The content and concentration of the three major pollen types (Artemisia, Chenopodiaceae and Ephedra) change with the mean annual precipitation, and the optimum mean annual precipitation for Ephedra, Chenopodiaceae and Artemisia is <80, 80200 and >160?mm, respectively. Correlation analysis between the variation in grain size of the three major pollen types and the main environmental variables shows that the grain size of the three pollen types is positively correlated with precipitation in the Qaidam Basin. The results confirm that precipitation is the most important environmental factor in the Qaidam Basin, and that it has an important effect on pollen grain size in the study area.
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| 4. |
- Xu, Qinghai, et al.
(författare)
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Studies of modern pollen assemblages for pollen dispersal- deposition- preservation process understanding and for pollen-based reconstructions of past vegetation, climate, and human impact : A review based on case studies in China
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 149, s. 151-166
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Tidskriftsartikel (refereegranskat)abstract
- Fossil pollen, as a direct proxy record of past vegetation, and indirect proxy record of past climate, plays an essential role in revealing and reconstructing past vegetation and climate. However, relationships between pollen, vegetation and climate are not linear, hence quantitative reconstructions of past vegetation and climate based on pollen records are not straightforward, and results may be highly contradictory and difficult to interpret. One of the main causes of discrepancies between results has been the lack of comprehensive and systematical studies on modern pollen dispersal and deposition processes, particularly on the quantification of these processes. Based on empirical studies performed in China over the last 30 years, this paper provides the state-of-the-art of the understanding of pollen dispersal and deposition processes in China and the remaining questions to be investigated. We show that major progress has been achieved in the study of modern pollen dispersal and deposition processes, and in the application of models of the pollen-vegetation-climate relationships for quantitative reconstruction of past vegetation and climate. However, several issues are not entirely solved or understood yet, such as how to quantify the reworking and re-deposition of pollen grains in quaternary alluvial sediments, the influence of pollen preservation on pollen assemblages, and human impact on vegetation. Even so, the progress made during the last decades makes it possible to achieve significantly more precise and informative reconstructions of past vegetation, land-use and climate in China than was possible earlier.
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