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  • 1
    Call number: AWI Bio-20-93988
    Type of Medium: Dissertations
    Pages: x, 181 Seiten , Illustrationen, Diagramme
    Language: English
    Note: Dissertation, Universität Potsdam, 2017 , Contents Abstract Kurzfassung Contents 1. List of figures 2. List of tables Chapter 1. General introduction 1. Motivation 2. Scientific background 3. Objectives of the thesis 4. Thesis outline Chapter 2. Manuscript 1: Treeline dynamics in Siberia under changing climates as inferred from an individual-based model for Larix 1. Abstract 2. Introduction 3. Material and Methods 4. Results 5. Discussion 6. Acknowledgements Chapter 3. Manuscript 2: Field and simulation data reveal dissimilar responses of Larix gmelinii stands to increasing temperature across the Siberian treeline ecotone 1. Abstract 2. Introduction 3. Methods 4. Results 5. Discussion 6. Acknowledgements Chapter 4. Manuscript 3: High gene flow and complex treeline dynamics on the Taymyr Peninsula (north-central Siberia), revealed by nuclear microsatellites of Larix 1. Abstract 2. Introduction 3. Materials and methods 4. Results 5. Discussion 6. Acknowledgements Chapter 5. Manuscript 4: Dispersal distances at treeline in Siberia - genetic guided model improvement 1. Abstract 2. Introduction 3. Methods 4. Results 5. Discussion 6. Acknowledgements Chapter 6. Synopsis 1. Towards a better understanding of Siberian treeline dynamics 2. Methodological challenges to reconstruct and predict the treeline advance 3. Conclusions 4. Outlook Appendix 1. Supplementary information for manuscript 1 (Chapter 2) 2. Supplementary information for manuscript 2 (Chapter 3) 3. Supplementary information for manuscript 3 (Chapter 4) 4. Supplementary information for manuscript 4 (Chapter 5) Bibliography Acknowledgements - Danksagung Declaration
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Standort 22 (1998), S. 27-30 
    ISSN: 1432-220X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2016-08-16
    Description: The prospected strong high-latitude warming is projected to cause a northward move of the arctic-boreal treeline. These changes will potentially have significant effects on climate, but their timing and mode are not well understood. Besides being governed directly by temperature increases, speed of treeline changes will also be influenced by the capacity of migration and establishment, and by competition between different treeline forming species. In Siberia, where about half of the global circum-arctic boreal treeline is located, the treeline is formed by monospecific stands of three species of larch, Larix sibirica, Larix gmelinii and Larix cajanderi. There is clear evidence for ecological separation, particularly between L. sibirica and the northeastern species, with only L. gmelinii and L. cajanderi being able to survive on permafrost with an active layer depth of less than 1-2 m, but L. sibirica being competitively superior at sites with low permafrost tables. Under a warming climate, the respective ranges of the treeline forming species are projected to shift to the Northeast, causing turnovers of forest tree species. The Siberian treeline has undergone several pronounced latitudinal fluctuations in the Holocene, and detailed analyses of the historical processes of vegetation change and competitive displacement would add to predictions for the projected future shift. We are using sedimentary ancient DNA to analyze lake sediment cores spanning most of the Holocene from the southern Taymyr peninsula, where the ranges of L. sibirica and L. gmelinii come together. Changes of the complete vegetation are revealed by DNA metabarcoding and pollen analyses, while diagnostic mitochondrial haplotypes trace the temporal dynamics in distribution of the two closely related larch species. We incorporated these two species into our larch population dynamics model LAVESI to understand the influence competition between these species might have on the speed and timing of treeline movement under changing climates. Simulations were forced with regional climate series at locations in the vicinity of the sampled lakes. These analyses offer a very high degree of resolution and shed light on the complicated ecological processes leading to a change in overall vegetation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 4
    Publication Date: 2017-07-13
    Description: The arctic-boreal treeline ecotone in Siberia is formed by monospecific stands of three species of larch, Larix sibirica, Larix gmelinii and Larix cajanderi. This area is currently under severe climatic pressure, and changes in forest density and extent are expected. Along with this, the respective ranges of the treeline forming species are projected to shift to the Northeast, which is only possible through migration and displacement of existing populations. Fluctuations in forest extent are known to have previously occurred during the Holocene, and investigations of these processes can aid our understanding of the dynamics of larch forests and the factors governing the distribution of the three species. While pollen records of Larix do not achieve a taxonomic resolution below the level of genus, this can be accomplished using genetic markers. We used sedimentary ancient DNA to analyze lake sediment cores spanning most of the Holocene from the southern Taymyr peninsula, where the ranges of L. sibirica and L. gmelinii come together. Changes of the complete vegetation were revealed by DNA metabarcoding and pollen analyses, while diagnostic mitochondrial haplotypes traced the temporal dynamics in distribution of the two closely related larch species. Additionally, we incorporated these two species into our larch population dynamics model LAVESI to understand the influence of competition between these species. Simulations were forced with regional climate series at locations in the vicinity of the sampled lakes. These analyses offer a high degree of resolution and shed light on the complicated ecological processes leading to a change in overall vegetation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
  • 6
    Publication Date: 2018-05-06
    Description: The Arctic is experiencing particularly high temperature increases, which will potentially cause major ecosystem changes, such as a northward expansion of boreal forests. About half of the global circum-arctic boreal treeline is located in Siberia, where it is formed by one of three species of larch, Larix sibirica, L. gmelinii and L. cajanderi, distributed from West to East, respectively. They hybridize in their boundary areas, but show ecological separation, especially with regard to survival on permafrost, and they differ in a number of other characteristics, such as growth rates and dispersal distances. Previously published models suggest an overall distributional shift of these species to the Northeast, as they track their climatic envelopes, but these projections do not consider biogeographical constraints or interspecific competition. Empirical data on past larch forest dynamics can aid here, as significant fluctuations in forest extent during the Holocene and Pleistocene are documented. DNA stored in sediments offers the possibility to obtain such data. Most analyses of environmental DNA employ metabarcoding techniques that provide an overview of biotic communities. As a consequence of targeting large groups, the genetic markers employed are limited in their taxonomic resolution, but within the sedimentary DNA we can also target much more variable markers to track dynamics of single species. We are using sedimentary ancient DNA to analyze past vegetation changes with DNA metabarcoding and the past distribution of single-nucleotide polymorphisms (SNPs) in mitochondrial and chloroplast DNA of Larix. On the southern Taymyr peninsula, where the ranges of L. sibirica and L. gmelinii come together, we trace temporal changes of mitochondrial haplotypes through most of the Holocene. A comparison of these results with simulations using the larch population dynamics model LAVESI indicate that projections including both the bioclimatic envelope and interspecific competition predicht climate change outcomes for larch forests more accurately.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    Publication Date: 2017-06-13
    Description: Arctic and alpine treelines worldwide differ in their reactions to climate change. A northward advance of or densification within the treeline ecotone will likely influence climate-vegetation feedback mechanisms. In our study, which was conducted in the Taimyr Depression in the North Siberian Lowlands, w present a combined field- and model-based approach helping us to better understand the population processes involved in the responses of the whole treeline ecotone, spanning from closed forest to single-tree tundra, to climate warming. Using information on stand structure, tree age, and seed quality and quantity from seven sites, we investigate effects of intra-specific competition and seed availability on the specific impact of recent climate warming on larch stands. Field data show that tree density is highest in the forest-tundra, and average tree size decreases from closed forest to single-tree tundra. Age-structure analyses indicate that the trees in the closed forest and forest-tundra have been present for at least ~240 years. At all sites except the most southerly ones, past establishment is positively correlated with regional temperature increase. In the single-tree tundra however, a change in growth form from krummholz to erect trees, beginning ~130 years ago, rather than establishment date has been recorded. Seed mass decreases from south to north, while seed quantity increases. Simulations with LAVESI (Larix Vegetation Simulator) further suggest that relative density changes strongly in response to a warming signal in the forest-tundra while intra-specific competition limits densification in the closed forest and seed limitation hinders densification in the single-tree tundra. We find striking differences in strength and timing of responses to recent climate warming. While forest-tundra stands recently densified, recruitment is almost non-existent at the southern and northern end of the ecotone due to autecological processes. Palaeo-treelines may therefore be inappropriate to infer past temperature changes at a fine scale. Moreover, a lagged treeline response to past warming will, via feedback mechanisms, influence climate change in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2017-06-16
    Description: Tree stands in the boreal treeline ecotone are, in addition to climate change, impacted by disturbances such as fire, water-related disturbances and logging. We aim to understand how these disturbances affect growth, age structure, and spatial patterns of larch stands in the north-eastern Siberian treeline ecotone (lower Kolyma River region), an insufficiently researched region. Stand structure of Larix cajanderi Mayr was studied at seven sites impacted by disturbances. Maximum tree age ranged from 44 to 300 years. Young to medium-aged stands had, independent of disturbance type, the highest stand densities with over 4000 larch trees per ha. These sites also had the highest growth rates for tree height and stem diameter. Overall lowest stand densities were found in a polygonal field at the northern end of the study area, with larches growing in distinct “tree islands”. At all sites, saplings are significantly clustered. Differences in fire severity led to contrasting stand structures with respect to tree, recruit, and overall stand densities. While a low severity fire resulted in low-density stands with high proportions of small and young larches, high severity fires resulted in high-density stands with high proportions of big trees. At waterdisturbed sites, stand structure varied between waterlogged and drained sites and latitude. These mixed effects of climate and disturbance make it difficult to predict future stand characteristics and the treeline position.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 9
    Publication Date: 2007-10-08
    Description: Existing structural, metamorphic and geochronological data in and close to the Shuswap Metamorphic Complex in the southern Canadian Cordillera are shown to be consistent with a channel flow model. Four general structural levels (domains) can be distinguished in the region, based on the orientation and vergence of folds. In the lowest three levels folds are mostly recumbent, whereas in the uppermost level they are upright. The lowest three levels are interpreted as a channel flow zone. NE-verging folds of the lowest level (Domain 1, e.g. the Monashee Complex) formed during top-to-the-NE detachment flow and/or in the lower part of a channel flow zone. When detachment flow changed to channel flow, the sense of shear changed in the upper part of the channel flow zone, resulting in overprinting of NE-verging folds by SW-verging folds (Domain 2, e.g. most parts of the Shuswap Metamorphic Complex to the west of the Monashee Complex). Temperature was probably increasing, weakening a progressively larger portion of the crust, and the crustal shear zone therefore widened. Thus, in the highest structural levels within the channel flow zone, SW-verging folds developed in areas where no NE-verging folds originally formed (Domain 3, e.g. the Cariboo Mountains). The channel flow model as presented here is compatible with many of the ductile structures and accommodates existing metamorphic and geochronological data in the part of the southern Canadian Cordillera described.
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  • 10
    Publication Date: 2016-09-01
    Description: A vegetation change from open tundra to dense taiga will fuel the global warming by positive feedback caused by albedo decreases. Yet, it is unclear how fast the arctic treeline, formed of Larix species, will advance north in the next decades. The most determinant factor of tree migration is the ability to disperse seeds (and pollen). Hence, to realistically forecast the migration of tree species in a dynamic vegetation model, it is crucial to incorporate reliable estimates of dispersal. Classical methods, for example counting seeds in seed traps, have been used to describe local dispersal abilities but are not applicable to give precise estimates on rare long-distance dispersal events. In this study we overcome this with the help of modern molecular techniques. By using a set of 16 nuclear microsatellites we inferred the cryptic signal of heritage among larch individuals to study the migration history among well-established tree stands and for different time-cohorts. We analyzed the genetic structure of larch populations for several latitudinal transects spanning north-to-south from tundra to open taiga forests in Siberia and additionally of several age cohorts which established throughout the last century in prevailing cold and warm periods. Finally, we present the results of simulations with our individual-based model LAVESI which was developed by us originally to study population dynamics of larch forest stands. Using downscaled global climate models and 'representative carbon pathway' (RCP) scenarios it is feasible to project the future treeline in Siberia.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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