| 1. |
- Feurdean, Angelica, et al.
(författare)
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The transformation of the forest steppe in the lower Danube Plain of southeastern Europe : 6000 years of vegetation and land use dynamics
- 2021
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 18:3, s. 1081-1103
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Tidskriftsartikel (refereegranskat)abstract
- Forest steppes are dynamic ecosystems, highly susceptible to changes in climate, disturbances and land use. Here we examine the Holocene history of the European forest steppe ecotone in the lower Danube Plain to better understand its sensitivity to climate fluctuations, fire and human impact, and the timing of its transition into a cultural forest steppe. We used multi-proxy analyses (pollen, n-alkanes, coprophilous fungi, charcoal and geochemistry) of a 6000- year sequence from Lake Oltina (southeastern Romania) combined with a REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model of quantitative vegetation cover. We found a greater tree cover, composed of xerothermic (Carpinus orientalis and Quercus) and temperate (Carpinus betulus, Tilia, Ulmus and Fraxinus) tree taxa, between 6000 and 2500 cal yr BP. Maximum tree cover (~50 %), dominated by C. orientalis occurred between 4200 and 2500 cal yr BP at a time of wetter climatic conditions and moderate fire activity. Compared to other European forest steppe areas, the dominance of C. orientalis represents the most distinct feature of the woodland's composition at this time. Tree loss was underway by 2500 yr BP (Iron Age), with the REVEALS model indicating a fall to ~20% tree cover from the Late Holocene forest maximum, linked to clearance for agriculture, while climate conditions remained wet. Biomass burning increased markedly at 2500 cal yr BP, suggesting that fire was regularly used as a management tool until 1000 cal yr BP when woody vegetation became scarce. A sparse tree cover, with only weak signs of forest recovery, then became a permanent characteristic of the lower Danube Plain, highlighting more or less continuous anthropogenic pressure. The timing of anthropogenic ecosystem transformation here (2500 cal yr BP) falls between that in centraleastern (between 3700 and 3000 cal yr BP) and eastern (after 2000 cal yr BP) Europe. Our study is the first quantitative land cover estimate at the forest steppe ecotone in southeastern Europe spanning 6000 years. It provides critical empirical evidence that, at a broad spatial scale, the present-day forest steppe and woodlands reflect the potential natural vegetation in this region under current climate conditions. However, the extent of tree cover and its composition have been neither stable in time nor shaped solely by the climate. Consequently, vegetation change must be seen as dynamic and reflecting wider changes in environmental conditions including natural disturbances and human impact.
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| 2. |
- Githumbi, Esther, et al.
(författare)
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European pollen-based REVEALS land-cover reconstructions for the Holocene : Methodology, mapping and potentials
- 2022
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 14:4, s. 1581-1619
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative reconstructions of past land cover are necessary to determine the processes involved in climate-human-land-cover interactions. We present the first temporally continuous and most spatially extensive pollen-based land-cover reconstruction for Europe over the Holocene (last 11g€¯700g€¯calg€¯yrg€¯BP). We describe how vegetation cover has been quantified from pollen records at a 11 spatial scale using the "Regional Estimates of VEgetation Abundance from Large Sites"(REVEALS) model. REVEALS calculates estimates of past regional vegetation cover in proportions or percentages. REVEALS has been applied to 1128 pollen records across Europe and part of the eastern Mediterranean-Black Sea-Caspian corridor (30-75° N, 25° W-50° E) to reconstruct the percentage cover of 31 plant taxa assigned to 12 plant functional types (PFTs) and 3 land-cover types (LCTs). A new synthesis of relative pollen productivities (RPPs) for European plant taxa was performed for this reconstruction. It includes multiple RPP values (≥2 values) for 39 taxa and single values for 15 taxa (total of 54 taxa). To illustrate this, we present distribution maps for five taxa (Calluna vulgaris, Cerealia type (t)., Picea abies, deciduous Quercus t. and evergreen Quercus t.) and three land-cover types (open land, OL; evergreen trees, ETs; and summer-green trees, STs) for eight selected time windows. The reliability of the REVEALS reconstructions and issues related to the interpretation of the results in terms of landscape openness and human-induced vegetation change are discussed. This is followed by a review of the current use of this reconstruction and its future potential utility and development. REVEALS data quality are primarily determined by pollen count data (pollen count and sample, pollen identification, and chronology) and site type and number (lake or bog, large or small, one site vs. multiple sites) used for REVEALS analysis (for each grid cell). A large number of sites with high-quality pollen count data will produce more reliable land-cover estimates with lower standard errors compared to a low number of sites with lower-quality pollen count data. The REVEALS data presented here can be downloaded from https://doi.org/10.1594/PANGAEA.937075 (Fyfe et al., 2022).
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| 3. |
- Grindean, Roxana, et al.
(författare)
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Relative pollen productivity estimates in the forest steppe landscape of southeastern Romania
- 2019
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier BV. - 0034-6667. ; 264, s. 54-63
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Tidskriftsartikel (refereegranskat)abstract
- Estimates of relative pollen productivity (RPP) represent key input parameters for model-based quantitative reconstructions of past vegetation cover. In this study, we provide the first RPP estimates for 13 taxa from the forest steppe ecoregion in southeastern Romania (southeastern Europe). We used modern pollen assemblages from 26 points together with vegetation surveys and mapping, covering a 1.5 km radius around each sampling site. We have estimated the relevant source area of pollen (RSAP) and pollen productivity for 13 taxa relative to Poaceae using the ERV (Extended R-value model), sub-model 3, as this model shows the best goodness of fit. The estimated RSAP is about 100 m and falls within the range of RSAP estimates of moss pollsters and forest hollows from other RPP-related studies. Results show that Rubiaceae (7.97), Apiaceae (5.91), Artemisia (5.89) and Fraxinus (2.99) are high pollen producers compared to Poaceae, while Plantago lanceolata (0.58), Fabaceae (0.40), Acer (0.30), Rosaceae (0.29), Carpinus orientalis (0.24), Cerealia (0.22) and Asteraceae (0.16) are low pollen producers with lower RPPs than Poaceae. Quercus (1.10) has a pollen productivity close to that of Poaceae. The RPPs for Carpinus orientalis and Fabaceae are published here the first time for Europe. The high pollen producing plants include both entomophilous and anemophilous species, while the low pollen producers are mostly entomophilous species. Our results form an essential contribution to improving the accuracy of quantitative reconstruction of forest steppe ecoregion in Europe and generally in regions with a similar climate and vegetation setting.
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