| 1. |
- Poska, Anneli, et al.
(author)
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Reading past landscapes : combining modern and historical records, maps, pollen-based vegetation reconstructions, and the socioeconomic background
- 2018
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In: Landscape Ecology. - : Springer Science and Business Media LLC. - 0921-2973 .- 1572-9761. ; 33:4, s. 529-546
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Journal article (peer-reviewed)abstract
- Context: Anthropogenic and environmental changes are reshaping landscapes across the globe. In this context, understanding the patterns, drivers, and consequences of these changes is one of the central challenges of humankind. Purpose: We aim to test the possibilities of combining modern multidisciplinary approaches to reconstruct the land-cover and linking the changes in land-cover to socioeconomic shifts in southern Estonia over the last 200 years. Methods: The historical records from five, and maps from six time periods and 79 pollen-based land-cover reconstructions from four lakes are used to determine the land-cover structure and composition and are thereafter combined with the literature based analyses of socioeconomic changes. Results: All information sources recorded similar changes in the land-cover. The anthropogenic deforestation was comparable to today’s (approximately 50%) during the nineteenth century. Major political and socioeconomic changes led to the intensification of agriculture and maximal deforestation (60–85%) at the beginning of the twentieth century. The land nationalisation following the Soviet occupation led to the reforestation of the less productive agricultural lands. This trend continued until the implementation of European Union agrarian subsidies at the beginning of the twenty first century. Conclusions: Pollen-based reconstructions provide a trustworthy alternative to historical records and maps. Accounting for source specific biases is essential when dealing with any data source. The landscape’s response to socioeconomic changes was considerable in Estonia over the last 200 years. Changes in land ownership and the global agricultural market are major drivers in determining the strength and direction of the land-cover change.
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| 2. |
- Poska, Anneli, et al.
(author)
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Timing and drivers of local to regional scale land-cover changes in the hemiboreal forest zone during the Holocene : A pollen-based study from South Estonia
- 2022
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 277
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Journal article (peer-reviewed)abstract
- Current land use and climate change pose a threat to the continued provision of ecosystem services expected from terrestrial land cover. Studies on past land-cover responses to such changes provide valuable information for future decisions. The hemiboreal zone, situated between temperate and boreal biomes, is a natural sensitivity hotspot for land cover change: it contains a continuous distribution limit of several temperate (Quercus robur, Tilia cordata, Fraxinus excelsior, Ulmus glabra, etc.) and some boreal (e.g. Picea abies) tree species. High resolution pollen data from three lakes in South Estonia, a hemiboreal zone in Northern Europe, was used to reconstruct the climate-driven dynamics of vegetation composition, anthropogenic deforestation, species-specific responses to climate cycles, and plant related environmental variables during the Holocene at a local and regional scale. The Landscape Reconstruction Algorithm (LRA) was used to reconstruct the vegetation composition, the Ellenberg Indicator Values for environmental reconstructions, and the Wavelet analysis for detecting cyclic patterns. The major land cover and environmental changes are in good accordance with the climate-based formal tripartite subdivision of the Holocene: a quick succession of tundra, boreal, and nemoral biomes during the Early Holocene, a dominance of temperate, broad-leaved forests during the Middle Holocene, and an expansion of mixed boreal forests and anthropogenic deforestation during the Late Holocene. Several episodes of compositional turnover ranging from a century (e.g., the transition from wet to dry tundra) to several millennia (e.g., the replacement of the temperate deciduous forests with boreal mixed forests) were identified. Our results show that local community changes have a shorter duration than the regional ones. The introduction of slash-and-burn agriculture caused abrupt forest composition changes at a local scale, promoting early successional tree species, even prior to the establishment of a permanently open cultural landscape. The only late successional tree species favoured by slash-and-burn cultivation was Picea abies. However, the application of more permanent cultivation strategies reduced its representation considerably. The determined cyclic changes in the proportions of tree taxa show, that most late successional trees exhibit high frequency (ca 200–400 year) cyclicity, probably reflecting the stand scale regeneration processes. The observed 1600 ± 200 and 1200 ± 200 year cycle changes in the occurrences of Quercus robur, Ulmus glabra and U. laevis, and Picea abies have a possible connection with a 1500 ± 500 year Bond cycle. Most of the tested tree taxa also had a statistically significant correlation with the ca 2200–2500 year Bray solar forcing cycle.
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| 3. |
- Rosentau, A., et al.
(author)
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A Holocene relative sea-level database for the Baltic Sea
- 2021
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 266
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Journal article (peer-reviewed)abstract
- We present a compilation and analysis of 1099 Holocene relative shore-level (RSL) indicators located around the Baltic Sea including 867 relative sea-level data points and 232 data points from the Ancylus Lake and the following transitional phase. The spatial distribution covers the Baltic Sea and near-coastal areas fairly well, but some gaps remain mainly in Sweden. RSL data follow the standardized HOLSEA format and, thus, are ready for spatially comprehensive applications in, e.g., glacial isostatic adjustment (GIA) modelling. We apply a SQL database system to store the nationally provided data sets in their individual form and to map the different input into the HOLSEA format as the information content of the individual data sets from the Baltic Sea area differs. About 80% of the RSL data is related to the last marine stage in Baltic Sea history after 8.5 ka BP (thousand years before present). These samples are grouped according to their dominant RSL tendencies into three clusters: regions with negative, positive and complex (transitional) RSL tendencies. Overall, regions with isostatic uplift driven negative tendencies dominate and show regression in the Baltic Sea basin during the last marine stage. Shifts from positive to negative tendencies in RSL data from transitional regions show a mid-Holocene highstand around 7.5-6.5 ka BP which is consistent with the end of the final melting of the Laurentide Ice Sheet. Comparisons of RSL data with GIA predictions including global ICE-5G and ICE-6G_C ice histories show good fit with RSL data from the regions with negative tendencies, whereas in the transitional areas in the eastern Baltic, predictions for the mid-Holocene clearly overestimate the RSL and fail to recover the midHolocene RSL highstand derived from the proxy reconstructions. These results motivate improvements of ice-sheet and Earth-structure models and show the potential and benefits of the new compilation for future studies. (C) 2021 The Authors. Published by Elsevier Ltd.
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| 4. |
- Vassiljev, Jüri
(author)
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Simulating the palaeorecord of northern European lakes using a coupled lake-catchment model
- 1997
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Doctoral thesis (other academic/artistic)abstract
- A coupled lake-catchment model was developed to examine the controls on lake-level changes in currently overflowing lakes during Holocene. The lake energy-balance is simulated as the one-dimensional vertical heat transfer by eddy diffusion and convective mixing. The accumulation and ablation of lake ice, and snow cover on the ice, is simulated thermodynamically. The lake water-balance is given by the balance between precipitation over the lake, evaporation from the water surface, catchment runoff, and lake outflow. Runoff is calculated using a one-dimensional, two layer soil covered by vegetation and a snowpack. Snow accumulation and ablation are controlled by air temperature. Outflow is controlled by the outlet size and outflow velocity, using the Manning equation. The coupled model was validated for Lake Bysjön (southern Sweden) and Lakes Karujärv and Viljandi (Estonia). The simulated monthly lake level matched observations of lake-level changes between 1944-1956 at Lake Viljandi (r=0.78), between 1976-1987 at Lake Karujärv (r=0.78) and between 1973-1977 at Lake Bysjön (r=0.7). The model was used to examine lake-level sensitivity to changes in individual climatic parameters. Changes in radiation, temperature, vapour pressure and wind strength produce lake-level changes of <0.5 m. Changes in mean annual and winter precipitation produce changes an order of magnitude larger. The lake-level sensitivity to precipitation changes is greatest when winter temperatures were higher than present. The magnitude of the response to a specific climatic change is strongly affected by the ratio of the lake area to the catchment area.
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| 5. |
- Väli, Vivika, et al.
(author)
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Multiscale pollen-based reconstructions of anthropogenic land-cover change in Karula Upland, south Estonia
- 2024
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In: Journal of Archaeological Science. - 0305-4403. ; 163
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Journal article (peer-reviewed)abstract
- Pollen-based quantitative vegetation reconstructions using multiple sedimentary basins from the same area, along with their quantified relevant pollen source areas, are a powerful means to study how long-term human impact has affected vegetation and shaped the currently protected heritage landscapes at different spatial scales. Our study presents the outcome of a palynological investigation in Karula Upland, south Estonia, for the last 6500 years. Centennial-resolution pollen records from one large (175 ha) and three small (5 ha) lakes, and one small bog (0.1 ha) were used to reconstruct the vegetation at different spatial scales using the Landscape Reconstruction Algorithm. The results are discussed in combination with archaeological sites and historical knowledge. The first signs of small-scale forest clearings connected to local human settlements are already visible in the Middle Stone Age (3100–4100 BCE). The first finds of cereal pollen (2500 BCE) from Lake Ähijärv suggest that grain crops were introduced to south Estonia during the Late Stone Age. The evidence of local crop farming in Karula is traceable since the Bronze Age. The widespread practice of slash-and-burn agriculture led to a major shift in land-cover with replacement of old-growth forests with the early-successional birch, occupying long-term fallows, during Late Bronze Age and Early Iron Age (700–250 BCE). A notable regression in farming is visible during the second part of the Early Iron Age (100–600 CE), with the most prominent change taking place around 500 CE, roughly coinciding with the 6th century Northern Hemisphere climate cooling and Migration Period. Permanent fields gained importance alongside slash-and-burn cultivation, during the Late Iron Age, ca 600–700 CE, shifting the vegetation composition towards more open land-cover. The ∼50 % open mosaic land-cover of the heritage landscape, protected today in Karula Upland, was formed during the Late Iron Age. The current study shows that sedimentary basins as close as ca 2 km from each other sometimes tell different stories, highlighting the need to quantify the size of the pollen source area to combine successfully archaeological, historical, and palynological evidence. Quantitative pollen-based vegetation reconstructions provide an environmental context for known, and possibly unknown, archaeological evidence within the pollen source area.
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