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  • 2020-2024  (7)
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  • 1
    Call number: AWI Bio-22-94840
    Description / Table of Contents: Vegetation change at high latitudes is one of the central issues nowadays with respect to ongoing climate changes and triggered potential feedback. At high latitude ecosystems, the expected changes include boreal treeline advance, compositional, phenological, physiological (plants), biomass (phytomass) and productivity changes. However, the rate and the extent of the changes under climate change are yet poorly understood and projections are necessary for effective adaptive strategies and forehanded minimisation of the possible negative feedbacks. The vegetation itself and environmental conditions, which are playing a great role in its development and distribution are diverse throughout the Subarctic to the Arctic. Among the least investigated areas is central Chukotka in North-Eastern Siberia, Russia. Chukotka has mountainous terrain and a wide variety of vegetation types on the gradient from treeless tundra to northern taiga forests. The treeline there in contrast to subarctic North America and north-western and central Siberia is represented by a deciduous conifer, Larix cajanderi Mayr. The vegetation varies from prostrate lichen Dryas octopetala L. tundra to open graminoid (hummock and non-hummock) tundra to tall Pinus pumila (Pall.) Regel shrublands to sparse and dense larch forests. Hence, this thesis presents investigations on recent compositional and above-ground biomass (AGB) changes, as well as potential future changes in AGB in central Chukotka. The aim is to assess how tundra-taiga vegetation develops under changing climate conditions particularly in Fareast Russia, central Chukotka. Therefore, three main research questions were considered: 1) What changes in vegetation composition have recently occurred in central Chukotka? 2) How have the above-ground biomass AGB rates and distribution changed in central Chukotka? 3) What are the spatial dynamics and rates of tree AGB change in the upcoming millennia in the northern tundra-taiga of central Chukotka? Remote sensing provides information on the spatial and temporal variability of vegetation. I used Landsat satellite data together with field data (foliage projective cover and AGB) from two expeditions in 2016 and 2018 to Chukotka to upscale vegetation types and AGB for the study area. More specifically, I used Landsat spectral indices (Normalised Difference Vegetation Index (NDVI), Normalised Difference Water Index (NDWI) and Normalised Difference Snow Index (NDSI)) and constrained ordination (Redundancy analysis, RDA) for further k-means-based land-cover classification and general additive model (GAM)-based AGB maps for 2000/2001/2002 and 2016/2017. I also used Tandem-X DEM data for a topographical correction of the Landsat satellite data and to derive slope, aspect, and Topographical Wetness Index (TWI) data for forecasting AGB. Firstly, in 2016, taxa-specific projective cover data were collected during a Russian-German expedition. I processed the field data and coupled them with Landsat spectral Indices in the RDA model that was used for k-means classification. I could establish four meaningful land-cover classes: (1) larch closed-canopy forest, (2) forest tundra and shrub tundra, (3) graminoid tundra and (4) prostrate herb tundra and barren areas, and accordingly, I produced the land cover maps for 2000/2001/2002 and 2016/20017. Changes in land-cover classes between the beginning of the century (2000/2001/2002) and the present time (2016/2017) were estimated and interpreted as recent compositional changes in central Chukotka. The transition from graminoid tundra to forest tundra and shrub tundra was interpreted as shrubification and amounts to a 20% area increase in the tundra-taiga zone and 40% area increase in the northern taiga. Major contributors of shrubification are alder, dwarf birch and some species of the heather family. Land-cover change from the forest tundra and shrub tundra class to the larch closed-canopy forest class is interpreted as tree infilling and is notable in the northern taiga. We find almost no land-cover changes in the present treeless tundra. Secondly, total AGB state and change were investigated for the same areas. In addition to the total vegetation AGB, I provided estimations for the different taxa present at the field sites. As an outcome, AGB in the study region of central Chukotka ranged from 0 kg m-2 at barren areas to 16 kg m-2 in closed-canopy forests with the larch trees contributing the highest. A comparison of changes in AGB within the investigated period from 2000 to 2016 shows that the greatest changes (up to 1.25 kg m 2 yr 1) occurred in the northern taiga and in areas where land cover changed to larch closed-canopy forest. Our estimations indicate a general increase in total AGB throughout the investigated tundra-taiga and northern taiga, whereas the tundra showed no evidence of change in AGB within the 15 years from 2002 to 2017. In the third manuscript, potential future AGB changes were estimated based on the results of simulations of the individual-based spatially explicit vegetation model LAVESI using different climate scenarios, depending on Representative Concentration Pathways (RCPs) RCP 2.6, RCP 4.5 and RCP 8.5 with or without cooling after 2300 CE. LAVESI-based AGB was simulated for the current state until 3000 CE for the northern tundra-taiga study area for larch species because we expect the most notable changes to occur will be associated with forest expansion in the treeline ecotone. The spatial distribution and current state of tree AGB was validated against AGB field data, AGB extracted from Landsat satellite data and a high spatial resolution image with distinctive trees visible. The simulation results are indicating differences in tree AGB dynamics plot wise, depending on the distance to the current treeline. The simulated tree AGB dynamics are in concordance with fundamental ecological (emigrational and successional) processes: tree stand formation in simulated results starts with seed dispersion, tree stand establishment, tree stand densification and episodic thinning. Our results suggest mostly densification of existing tree stands in the study region within the current century in the study region and a lagged forest expansion (up to 39% of total area in the RCP 8.5) under all considered climate scenarios without cooling in different local areas depending on the closeness to the current treeline. In scenarios with cooling air temperature after 2300 CE, forests stopped expanding at 2300 CE (up to 10%, RCP 8.5) and then gradually retreated to their pre-21st century position. The average tree AGB rates of increase are the strongest in the first 300 years of the 21st century. The rates depend on the RCP scenario, where the highest are as expected under RCP 8.5. Overall, this interdisciplinary thesis shows a successful integration of field data, satellite data and modelling for tracking recent and predicting future vegetation changes in mountainous subarctic regions. The obtained results are unique for the focus area in central Chukotka and overall, for mountainous high latitude ecosystems.
    Type of Medium: Dissertations
    Pages: 149 Seiten , Illustrationen, Diagramme
    Language: English
    Note: Dissertation, Potsdam, Universität Potsdam, 2022 , Contents Abstract Zusammenfassung Contents Abbreviations Motivation 1 Introduction 1.1 Scientific background 1.2 Study region 1.3 Aims and objectives 2 Materials and methods 3.1 Section 4 - Strong shrub expansion in tundra-taiga, tree infilling in taiga and stable tundra in central Chukotka (north-eastern Siberia) between 2000 and 2017 3.2 Section 5 - Recent above-ground biomass changes in central Chukotka (NE Siberia) combining field-sampling and remote sensing 3.3 Section 6 - Future spatially explicit tree above-ground biomass trajectories revealed for a mountainous treeline ecotone using the individual-based model LAVESI 4 Strong shrub expansion in tundra-taiga, tree infilling in taiga and stable tundra in central Chukotka (north-eastern Siberia) between 2000 and 2017 Abstract 1 Introduction 2 Materials and methods 2.1 Field data collection and processing 2.2 Landsat data, pre-processing and spectral indices processing 2.3 Redundancy analysis (RDA) and classification approaches 3 Results 3.1 General characteristics of the vegetation field data 3.2 Relating field data to Landsat spectral indices in the RDA model 3.3 Land-cover classification 3.4 Land-cover change between 2000 and 2017 4 Discussion 4.1 Dataset limitations and optimisation 4.2 Vegetation changes from 2000/2001/2002 to 2016/2017 Conclusions Acknowledgements Data availability statement References Appendix A. Detailed description of Landsat acquisitions Appendix B. MODIS NDVI time series from 2000 to 2018 Appendix C. Landsat Indices values for each analysed vegetation site Appendix D. Fuzzy c-means classification for interpretation of uncertainties for land-cover mapping Appendix E. Validation of land-cover maps Appendix F. K-means classification results Appendix G. Heterogeneity of natural landscapes and mixed pixels of satellite data Appendix H. Distribution of land-cover classes and their changes by study area 5 Recent above-ground biomass changes in central Chukotka (NE Siberia) combining field-sampling and remote sensing Abstract 1 Introduction 2 Materials and methods 2.1 Study region and field surveys 2.2 Above-ground biomass upscaling and change derivation 3 Results 3.1 Vegetation composition and above-ground biomass 3.2 Upscaling above-ground biomass using GAM 3.3 Change of above-ground biomass between 2000 and 2017 in the four focus areas 4 Discussion 4.1 Recent state of above-ground biomass at the field sites 4.2 Recent state of above-ground biomass upscaled for central Chukotka 4.3 Change in above-ground biomass within the investigated 15–16 years in central Chukotka 5 Conclusions Data availability statement Author contributions Competing interests Acknowledgements References Appendix A. Sampling and above-ground biomass (AGB) calculation protocol for field data 6 Future spatially explicit tree above-ground biomass trajectories revealed for a mountainous treeline ecotone using the individual-based model LAVESI Abstract 1 Introduction 2 Materials and methods 2.1 Study region 2.2 LAVESI model setup, parameterisation, and validation 2.2.4 LAVESI simulation setup for this study 2.2.5 Validation of the model’s performance 3 Results 3.1 Dynamics and spatial distribution changes of tree above-ground-biomass 3.2 Spatial and temporal validation of the contemporary larch AGB 4 Discussion 4.1 Future dynamics of tree AGB at a plot level 4.2 What are the future dynamics of tree AGB at the landscape level? 5 Conclusions Data availability Acknowledgements References Appendix B. Permutation tests for tree presence versus topographical parameters Appendix C. Landsat-based, field, and simulated estimations of larch above-ground biomass (AGB). 7 Synthesis 7.1 What changes in vegetation composition have happened from 2000 to 2017 in central Chukotka? 7.2 How have the above-ground biomass (AGB) distribution and rates changed from 2000 to 2017 in central Chukotka? 7.3 What are the spatial dynamics and rates of tree AGB change in the upcoming centuries in the northern tundra-taiga from 2020 to 3000 CE on the plot level and landscape level? References Acknowledgements
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  • 2
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    Johns Hopkins University Press
    Publication Date: 2022-07-15
    Description: Though the fall of the Soviet Union opened the way for states in central and eastern Europe to join the world of market-oriented Western democracies, the expected transitions have not been as easy, common, or smooth as sometimes perceived. Rachel A. Epstein investigates how liberal ideas and practices are embedded in transitioning societies and finds that success or failure depends largely on creating a social context in which incentives held out by international institutions are viewed as symbols of an emerging Western identity in the affected country.Epstein first explains how a liberal worldview and institutions like the European Union, World Bank, the International Monetary Fund, and the North Atlantic Treaty Organization go hand-in-hand and why Western nations assume that a broad and incremental program of incentives to join will encourage formerly authoritarian states to reform their political and economic systems. Using Hungary, Poland, Romania, and the Ukraine as case studies, she demonstrates the limits of conditionality in the face of national social perceptions and elucidates the three key points around which a consensus within the state must emerge before international institutions can expect liberalization: domestic officials must be uncertain about how changing policies will affect their interests; the status of international and domestic institutions must not be in jeopardy; and the proposed polices must seem credible. In making her case, Epstein cleverly bridges the gap between the rationalist and constructivist schools of thought.Offering new data on and fresh interpretations of reforming central bank policies, privatizing banks with foreign capital, democratizing civil-military relations, and denationalizing defense policy, In Pursuit of Liberalism extends well beyond the scope of previous book-length studies.
    Keywords: Comparative politics ; bic Book Industry Communication::J Society & social sciences::JP Politics & government::JPB Comparative politics
    Language: English
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  • 3
    Publication Date: 2024-03-29
    Description: The Implementing Standards-Based Accountability (ISBA) study was designed to examine the strategies that states, districts, and schools are using to implement standards-based accountability under the No Child Left Behind Act (NCLB). This monograph presents information regarding the implementation of NCLB in California, Georgia, and Pennsylvania from 2003-2004 through 2005-2006, including the final results of the ISBA project.
    Keywords: Sociology ; Education ; bic Book Industry Communication::J Society & social sciences::JN Education::JNF Educational strategies & policy ; bic Book Industry Communication::J Society & social sciences::JF Society & culture: general::JFS Social groups::JFSP Age groups::JFSP1 Age groups: children ; thema EDItEUR::J Society and Social Sciences::JN Education::JNF Educational strategies and policy ; thema EDItEUR::J Society and Social Sciences::JB Society and culture: general::JBS Social groups, communities and identities::JBSP Age groups and generations::JBSP1 Age groups: children
    Language: English
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  • 4
    Publication Date: 2024-03-29
    Description: For three school years, from 2007 to 2010, about 200 high-needs New York City public schools participated in the Schoolwide Performance Bonus Program, whose broad objective was to improve student performance through school-based financial incentives. An independent analysis of test scores, surveys, and interviews found that the program did not improve student achievement, perhaps because it did not motivate change in educator behavior.
    Keywords: Education ; bic Book Industry Communication::J Society & social sciences::JN Education::JNK Organization & management of education::JNKD Examinations & assessment ; bic Book Industry Communication::J Society & social sciences::JN Education::JNF Educational strategies & policy ; thema EDItEUR::J Society and Social Sciences::JN Education::JND Educational systems and structures::JNDH Education: examinations and assessment ; thema EDItEUR::J Society and Social Sciences::JN Education::JNF Educational strategies and policy
    Language: English
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  • 5
    Publication Date: 2024-03-30
    Description: Launched by the U.S. Army Reserve, the Employer Partnership Program (EPP) supports reservists and their civilian employers. It features a job search website that allows employers to recruit among reservists, veterans, and family members. The study analyzed data collected through September 2010 from the EPP’s job search website, conducted case studies of Army Reserve units located in four metropolitan areas, and interviewed program stakeholders.
    Keywords: Technology ; Law
    Language: English
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  • 6
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    American Meteorological Society
    In:  EPIC3Bulletin of the American Meteorological Society, American Meteorological Society, 104(9), pp. s1-s10, ISSN: 0003-0007
    Publication Date: 2024-05-29
    Description: 〈jats:title〉Abstract〈/jats:title〉 〈jats:p〉—J. BLUNDEN, T. BOYER, AND E. BARTOW-GILLIES〈/jats:p〉 〈jats:p〉Earth’s global climate system is vast, complex, and intricately interrelated. Many areas are influenced by global-scale phenomena, including the “triple dip” La Niña conditions that prevailed in the eastern Pacific Ocean nearly continuously from mid-2020 through all of 2022; by regional phenomena such as the positive winter and summer North Atlantic Oscillation that impacted weather in parts the Northern Hemisphere and the negative Indian Ocean dipole that impacted weather in parts of the Southern Hemisphere; and by more localized systems such as high-pressure heat domes that caused extreme heat in different areas of the world. Underlying all these natural short-term variabilities are long-term climate trends due to continuous increases since the beginning of the Industrial Revolution in the atmospheric concentrations of Earth’s major greenhouse gases.〈/jats:p〉 〈jats:p〉In 2022, the annual global average carbon dioxide concentration in the atmosphere rose to 417.1±0.1 ppm, which is 50% greater than the pre-industrial level. Global mean tropospheric methane abundance was 165% higher than its pre-industrial level, and nitrous oxide was 24% higher. All three gases set new record-high atmospheric concentration levels in 2022.〈/jats:p〉 〈jats:p〉Sea-surface temperature patterns in the tropical Pacific characteristic of La Niña and attendant atmospheric patterns tend to mitigate atmospheric heat gain at the global scale, but the annual global surface temperature across land and oceans was still among the six highest in records dating as far back as the mid-1800s. It was the warmest La Niña year on record. Many areas observed record or near-record heat. Europe as a whole observed its second-warmest year on record, with sixteen individual countries observing record warmth at the national scale. Records were shattered across the continent during the summer months as heatwaves plagued the region. On 18 July, 104 stations in France broke their all-time records. One day later, England recorded a temperature of 40°C for the first time ever. China experienced its second-warmest year and warmest summer on record. In the Southern Hemisphere, the average temperature across New Zealand reached a record high for the second year in a row. While Australia’s annual temperature was slightly below the 1991–2020 average, Onslow Airport in Western Australia reached 50.7°C on 13 January, equaling Australia's highest temperature on record.〈/jats:p〉 〈jats:p〉While fewer in number and locations than record-high temperatures, record cold was also observed during the year. Southern Africa had its coldest August on record, with minimum temperatures as much as 5°C below normal over Angola, western Zambia, and northern Namibia. Cold outbreaks in the first half of December led to many record-low daily minimum temperature records in eastern Australia.〈/jats:p〉 〈jats:p〉The effects of rising temperatures and extreme heat were apparent across the Northern Hemisphere, where snow-cover extent by June 2022 was the third smallest in the 56-year record, and the seasonal duration of lake ice cover was the fourth shortest since 1980. More frequent and intense heatwaves contributed to the second-greatest average mass balance loss for Alpine glaciers around the world since the start of the record in 1970. Glaciers in the Swiss Alps lost a record 6% of their volume. In South America, the combination of drought and heat left many central Andean glaciers snow free by mid-summer in early 2022; glacial ice has a much lower albedo than snow, leading to accelerated heating of the glacier. Across the global cryosphere, permafrost temperatures continued to reach record highs at many high-latitude and mountain locations.〈/jats:p〉 〈jats:p〉In the high northern latitudes, the annual surface-air temperature across the Arctic was the fifth highest in the 123-year record. The seasonal Arctic minimum sea-ice extent, typically reached in September, was the 11th-smallest in the 43-year record; however, the amount of multiyear ice—ice that survives at least one summer melt season—remaining in the Arctic continued to decline. Since 2012, the Arctic has been nearly devoid of ice more than four years old.〈/jats:p〉 〈jats:p〉In Antarctica, an unusually large amount of snow and ice fell over the continent in 2022 due to several landfalling atmospheric rivers, which contributed to the highest annual surface mass balance, 15% to 16% above the 1991–2020 normal, since the start of two reanalyses records dating to 1980. It was the second-warmest year on record for all five of the long-term staffed weather stations on the Antarctic Peninsula. In East Antarctica, a heatwave event led to a new all-time record-high temperature of −9.4°C—44°C above the March average—on 18 March at Dome C. This was followed by the collapse of the critically unstable Conger Ice Shelf. More than 100 daily low sea-ice extent and sea-ice area records were set in 2022, including two new all-time annual record lows in net sea-ice extent and area in February.〈/jats:p〉 〈jats:p〉Across the world’s oceans, global mean sea level was record high for the 11th consecutive year, reaching 101.2 mm above the 1993 average when satellite altimetry measurements began, an increase of 3.3±0.7 over 2021. Globally-averaged ocean heat content was also record high in 2022, while the global sea-surface temperature was the sixth highest on record, equal with 2018. Approximately 58% of the ocean surface experienced at least one marine heatwave in 2022. In the Bay of Plenty, New Zealand’s longest continuous marine heatwave was recorded.〈/jats:p〉 〈jats:p〉A total of 85 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, close to the 1991–2020 average of 87. There were three Category 5 tropical cyclones across the globe—two in the western North Pacific and one in the North Atlantic. This was the fewest Category 5 storms globally since 2017. Globally, the accumulated cyclone energy was the lowest since reliable records began in 1981. Regardless, some storms caused massive damage. In the North Atlantic, Hurricane Fiona became the most intense and most destructive tropical or post-tropical cyclone in Atlantic Canada’s history, while major Hurricane Ian killed more than 100 people and became the third costliest disaster in the United States, causing damage estimated at $113 billion U.S. dollars. In the South Indian Ocean, Tropical Cyclone Batsirai dropped 2044 mm of rain at Commerson Crater in Réunion. The storm also impacted Madagascar, where 121 fatalities were reported.〈/jats:p〉 〈jats:p〉As is typical, some areas around the world were notably dry in 2022 and some were notably wet. In August, record high areas of land across the globe (6.2%) were experiencing extreme drought. Overall, 29% of land experienced moderate or worse categories of drought during the year. The largest drought footprint in the contiguous United States since 2012 (63%) was observed in late October. The record-breaking megadrought of central Chile continued in its 13th consecutive year, and 80-year record-low river levels in northern Argentina and Paraguay disrupted fluvial transport. In China, the Yangtze River reached record-low values. Much of equatorial eastern Africa had five consecutive below-normal rainy seasons by the end of 2022, with some areas receiving record-low precipitation totals for the year. This ongoing 2.5-year drought is the most extensive and persistent drought event in decades, and led to crop failure, millions of livestock deaths, water scarcity, and inflated prices for staple food items.〈/jats:p〉 〈jats:p〉In South Asia, Pakistan received around three times its normal volume of monsoon precipitation in August, with some regions receiving up to eight times their expected monthly totals. Resulting floods affected over 30 million people, caused over 1700 fatalities, led to major crop and property losses, and was recorded as one of the world’s costliest natural disasters of all time. Near Rio de Janeiro, Brazil, Petrópolis received 530 mm in 24 hours on 15 February, about 2.5 times the monthly February average, leading to the worst disaster in the city since 1931 with over 230 fatalities.〈/jats:p〉 〈jats:p〉On 14–15 January, the Hunga Tonga-Hunga Ha'apai submarine volcano in the South Pacific erupted multiple times. The injection of water into the atmosphere was unprecedented in both magnitude—far exceeding any previous values in the 17-year satellite record—and altitude as it penetrated into the mesosphere. The amount of water injected into the stratosphere is estimated to be 146±5 Terragrams, or ∼10% of the total amount in the stratosphere. It may take several years for the water plume to dissipate, and it is currently unknown whether this eruption will have any long-term climate effect.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 7
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    American Meteorological Society
    In:  EPIC3Bulletin of the American Meteorological Society, American Meteorological Society, 104(9), pp. s271-s321, ISSN: 0003-0007
    Publication Date: 2024-05-29
    Repository Name: EPIC Alfred Wegener Institut
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