Doktorsritgerðir - LBHÍ

Varanleg URI fyrir þennan undirflokkhttps://hdl.handle.net/20.500.11815/89

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Niðurstöður 1 - 9 af 9

Soil dynamics within Icelandic birch woodland chronosequences
(2025) Sanchez, Sólveig; Arnalds, Ólafur; Thorsson, Jóhann; Dahlgren, Randy; Aradóttir, Ása L.; Faculty of Environmental and Forest Sciences
The reduction of natural woodland cover in the world has led to a significant deterioration in soil fertility and disruption of soil nutrient cycles. In Iceland, land degradation increased vastly after the erasure of mountain birch woodlands, the country’s only native forest-forming tree species. The Icelandic government aims to restore part of these lost woodlands. This thesis seeks to fill important knowledge gaps regarding birch woodland soils in relation to woodland restoration. Ten birch woodland chronosequences (non-forested to 60+ years old woodlands) across the country were investigated, with a focus on soil organic carbon (SOC), soil chemical and colloidal constituents, and hydrological processes. The soils are typical Andisols with a colloidal fraction dominated by allophane, ferrihydrite, and mineral-organic complexes (MOCs). The research revealed that allophane in the soils had extremely variable Al/Si ratios, which were related to influences of soil age, dust accumulation rates, and soil pH. The results showed significant SOC sequestration in old birch woodland soils, with carbon stocks of 7.4 kg/m2 in the top 30 cm (significantly higher than non-forested sites: 5.0 kg/m2), and a yearly SOC accumulation of 0.04-0.07 kg/m2/yr. The rapid increase was mostly attributed to andic soil properties and bonds with soil colloids, including MOCs, which enhanced SOC stability. Ferrihydrite was more abundant in the soils than was expected and had an influence on carbon dynamics. The restoration of birch woodlands to 5% of the land cover would lead to a SOC sequestration totaling 7% of the country’s current greenhouse gas emissions. The water retention capacities of the old woodlands were also the highest in this study (FC 63.5%, WP 45.6% on average), with excessively rapid infiltration rates (>586 mm/h in summer). This can be explained by the site’s porous soils and rich vegetation cover, which assisted the water inflow and prevented ice blockage during winter (a key factor for hydrological soil health). Dust emerged as an influential factor on soil properties, such as carbon dynamics and Al/Si ratios of allophane, and by buffering the soil pH. Dust deposition buries carbon (up to 0.026 kg/m2/yr in the highest dust categories), contributing to SOC accumulation. In general, natural birch woodlands in Iceland positively impact soil quality, as their soils are carbon-rich, fertile systems, with optimal hydrological properties. Their conservation and restoration are of fundamental environmental value in Iceland today and for Iceland of tomorrow.
Effects of soil warming on growth processes of unmanaged subarctic grasslands
(Agricultural University of Iceland, 2025-05-30) Tchana Wandji, Ruth Phoebe; Pr. Bjarni D Sigurdsson, Dr. Peter Lootens, Dr Iolanda Filella; Environmental and Forest Science
High-latitude plant growth processes involve a range of physiological and biochemical mechanisms that allow plants to progress during relatively short growing seasons from unmature to fully developed organisms capable of reproducing. During the past decades, terrestrial ecosystems have experienced a lot of alterations from climate change, and high latitude ecosystems are affected at a faster pace compared to other terrestrial ecosystems. Therefore, it is important to study how further warming is likely to affect high-latitude plant communities, including Iceland. There are now 18 whole-soil warming experiments ongoing worldwide to increase our understanding of how plant and soil communities are likely to respond to further climate warming, and the ForHot research site is one of them. It utilises warm bedrocks below the soil profiles of known age to study the impacts of soil warming. The ForHot contains six ecosystem-level field experiments that involve different amounts of soil warming, duration of warming and N-availability in different vegetation communities. Whereof I used two grassland experiments. That is, the medium-term warming (MTW) site that has been warm since 2008 and the long-term warming (LTW) site with the same type of grassland, but where the warming has been ongoing for >60 years. To understand how subarctic grassland growth processes respond to soil warming, I looked at the first step in the plant growth processes, that is, the responses in the photosynthetic system. Secondly, I studied the duration of vegetation activity (phenology) throughout the growing season with both traditional and remote-sensing methods. Lastly, I investigated how soil warming and interannual variation affected the aboveground net primary productivity (ANPP). The main outcomes were that even if the photosynthetic capacity remained unaltered per unit leaf area under warmer conditions, the amount of community leaf area over each m2 of surface (NDVI) increased and the duration of growth lengthened with warming. Which likely resulted together in more seasonal carbon uptake and the observed increases in ANPP under warming in both grasslands. Nevertheless, the increasing ANPP was associated with a “down-regulation” at the higher warming levels, which was possibly linked to N losses from the warmed soils. Duration of warming was generally not found to be important in plant aboveground responses.
Exploring the Genetic Regulation of Ability and Quality of Gaits in Icelandic Horses
(2025-01) Sigurðardóttir, Heiðrún; Main academic supervisors: Dr. Susanne Eriksson, Department of Animal Biosciences and SLU Dr. Þorvaldur Kristjánsson, The Agricultural University of Iceland. Co-supervisors: Dr. Gabriella Lindgren, Department of Animal Biosciences, SLU; Dr. Elsa Albertsdóttir, Independent researcher and Dr. Marie Rhodin, Department of Animal Biosciences, SLU; Land use & cultivation (AUI); Department of Animal Biosciences (SLU); Faculty of Agricultural Sciences (AUI); Faculty of Veterinary Medicine and Animal Science (SLU)
Abstract: The Icelandic horse is celebrated for its unique gaits and versatility as a riding horse, yet the genetic basis of these characteristics is not fully understood. Its diverse gait range, the availability of extensive phenotypic records, and the application of advanced genomic technologies make the Icelandic horse an invaluable model for exploring the genetic foundations of gait traits and performance. This thesis aimed to identify novel genetic factors affecting gaits and performance in the Icelandic horse by integrating genomic approaches to analyse genetic variation through genome-wide patterns of homozygosity and polymorphic variation. The study utilized high-density SNP genotype data, generated using a 670k genotype array, from 380 horses to perform genome-wide association (GWA) studies and runs of homozygosity (ROH) analyses. Additionally, 39 horses were included for whole-genome sequencing (WGS) analysis. Through GWA studies, quantitative trait loci (QTLs) affecting gait traits were identified. One QTL was associated with breeding scores for back and croup conformation, which significantly influenced the quality of the lateral gaits tölt and pace. Two additional QTLs were directly linked to breeding scores for pace. Haplotype analysis revealed two frequent haplotypes for each identified QTL that had significant effects on the associated trait. The haplotypes associated with back and croup harboured genes with known roles in muscle and skeletal development in humans. The haplotypes affecting pace scores were located within the candidate genes STAU2 and RELN which are expressed in neural tissue. In addition to the observed effects on pace, the STAU2 haplotypes were found to significantly influence the quality of trot and gallop, while the RELN haplotypes impacted the quality of tölt, trot, canter, and gallop, and may potentially also influence the trainability and precocity of young horses. Moreover, interactions between STAU2, RELN, and the previously identified DMRT3 gene were observed, involving both additive and compensatory effects. Sequence analysis in these regions revealed a partial loss of the STAU2 protein caused by a one-base-pair frameshift insertion. This variant was proposed to be causative for the observed effects of the STAU2 haplotypes. In the RELN region, potential regulatory elements were identified and suggested as candidate variants influencing the effects of the RELN haplotypes. The enduring significance of the genomic region on ECA23, harbouring the DMRT3 gene, was confirmed through ROH analysis, while additional regions of potential relevance to performance traits were identified. Analyses of genomic inbreeding and genetic diversity indicated that recent breeding practices in the Icelandic horse breed have been sustainable, maintaining adequate genetic diversity. In conclusion, this thesis expands current knowledge of the genetic basis of gait and performance in the Icelandic horse, by demonstrating that genetic factors beyond DMRT3 contribute to the regulation of gait ability and quality. The findings warrant further investigations and may ultimately benefit the breeding of the Icelandic horse and assist breeders in making more informed breeding decisions.
The impact of spatio-temporal shifts in vertebrate herbivore communities on the functioning the Icelandic tundra
(2024-12) Defourneaux, Mathilde; Faculty of Environmental and Forest Sciences
Rapid environmental changes in the Arctic tundra are driving shifts in herbivore populations, distribution, and phenology, affecting the structure of herbivore community. These changes will have consequences to ecosystem structure and function through the direct effects of herbivores on vegetation biomass and biogeochemical cycles. Yet, the effects of herbivores on ecosystem functions, particularly within a multispecies context, are still poorly understood. Addressing these knowledge gaps in tundra rangelands, which are grazed by both wild and domestic herbivores, is an urgent task to ensure the development of sustainable management practices. Using Icelandic rangelands as a case study, I investigated how changes in herbivore communities affect tundra ecosystem functions across various spatial and temporal scales, with a focus on nutrient recycling. Specifically, I aimed to: 1) track changes in herbivore community composition through time, 2) assess the impact of herbivore on vegetation biomass, 3) measure the faecal nutrient contributions of different herbivores species, and 4) evaluate the role of herbivores on nutrient distribution. I analysed long-term data to assess shifts in herbivore populations and their impacts on vegetation at a regional scale. Additionally, through extensive fieldwork in 2022, I examined herbivore effects on vegetation, faecal nutrient deposition, and nutrient transport at landscape and local scales in high-elevation rangelands. Specifically, I measured rates of aboveground biomass consumption, faecal nutrient content and faecal deposition rates of pink-footed goose, sheep and reindeer, and forage quality at 21 sampling sites throughout the growing season. Near-infrared reflectance spectroscopy (NIRS) models were calibrated to estimate faecal nutrient content. Results from the thesis indicate rapid changes in the Icelandic herbivore community: over the past 40 years, the dominant herbivores shifted from domestic (mainly sheep) to wild herbivores, led by the large increase in pinkfooted goose. Overall, herbivores consumed a small percentage (4%) of total plant biomass, but this reached up to 30% in localised areas in the Eastern Highlands toward the end of the growing season. Although the goose population consumed less biomass than the sheep population, geese contributed significantly more to faecal nutrient deposition, especially early in the growing season when nutrient content in their faeces was highest. There was no clear connection between forage quality and herbivore consumption, but areas with low-quality forage showed more nutrient deposition through faeces. These findings highlight the potential of herbivores to redistribute nutrient across the landscape and provide insights into the role of herbivores in shaping tundra ecosystems through their effects on nutrient cycling, particularly in the context of strong and rapid ongoing herbivore community changes.
Public participation in marine spatial planning in Iceland
(2024-03-14) Wilke, Maria; Dr Sigríður Kristjánsdóttir, Dr Ragnheiður I. Þórarinsdóttir; Department of Planning and Design
As the global climate is changing dramatically, Northern communities are facing a multitude of challenges including changing weather patterns, sea level rise and invasive species. To cope with the recent climatic changes - many of which present great uncertainties to livelihoods - strategies should be developed to plan and adapt for the future. Iceland has recently launched marine spatial planning (MSP) endeavours, and two of the first planning processes have been conducted. MSP presents opportunities for authorities, stakeholders, and the public to come together to forge a sustainable path ahead for marine areas that are under increasing pressure from human activities. MSP aims at ecosystem-based management of ocean resources that brings different stakeholders and the public together to discuss their conflicts of interest and forge a sustainable path forward. Public participation is a crucial element of MSP to make it democratically legitimate and sustainable in the long-term. However, MSP comes with its own considerable challenges as it attempts to engage stakeholders and the general public in decisions about an ‘invisible’ space largely beneath the surface of the sea. MSP was formally introduced by law in Iceland in 2018 and two projects were initiated in the Westfjords and Eastfjords in 2019, with one further planned in Skjálfandi Bay. This dissertation explores MSP in Iceland in three research articles. In paper I, the uncertainties of the environmental changes in the Westfjords are explored in conjunction with the multitude of societal challenges to coastal and marine planning in Iceland. Data from the planning documents as well as from semi-structured interviews and a workshop conducted in the Westfjords are analysed and discussed to establish how environmental changes and the societal context set the scene for Icelandic MSP. To assess the scope and depth of public participation in the Icelandic MSP process, paper II presents data that was collected through participant observation, unstructured and semi- structured interviews (n=80) and document analysis in the three case studies. The results show that a limited group of people including institutional actors and formal stakeholders had been engaged in the information gathering stages of the process, but in the later phases of discussion and decision-making, local community members were notably absent. This lack of public participation highlights the need for more in-depth communication about the MSP process and marine issues in the adjacent communities as well as an urgent need for inclusion of the public into marine decision-making and MSP. Whereas marine spatial planning is new to Iceland, coastal zone planning (CZP) is well established in Norway. Paper III investigates how participation in coastal and marine planning viii processes compare between Iceland and Norway, and what lessons can be shared between them. Data was collected in two case studies in the Tromsø region in Norway and the Westfjords of Iceland through analysis of planning documentation, literature review and semi-structured interviews. The results show that public participation is formally integral to both processes, but in practice varies considerably. Both planning processes are driven by the expansion of the aquaculture industry and a variety of issues faced during the planning process are similar. However, divergent frameworks of the planning processes result in major differences between the implementations and their implications for local communities. In Norway, public participation is politically desired and guided by a participation strategy, emphasising synergies between expert and local knowledge. In the Tromsø region, meaningful public participation varied across the involved municipalities and issues regarding indigenous participation remain. In Iceland, there is little evident political expectation of public engagement, and the process is characterised by a passive approach to participation that aims to inform the public but does not include wider sharing of decision-making power.
Alleles of adaptive importance for barley cultivation in a subarctic climate
(2023-05) Göransson, Magnus; Jón Hallsteinn Hallsson, Morten Lillemo, Åsmund Bjørnstad, Gunter Backes; Department of Plant Sciences; Department of Agriculture
Patterns and drivers of rangeland degradation in Mongolia
(2022) Sainnemekh, Sumjidmaa; Isabel C Barrio, Ása L. Aradóttir, Brandon Bestelmeyer, Bulgamaa Densambuu; ; Faculty of Environmental and Forest Sciences
Rangelands are currently facing increasing threats from climate change, overgrazing and land conversion and rangeland degradation is a growing concern worldwide. The ability of degraded rangelands to provide the natural resources needed to sustain pastoralists and ensure the persistence of traditional nomadic lifestyles is less than that of healthy rangelands. In Mongolia, serious concerns have emerged in recent decades about the accelerating rate of rangeland degradation. Understanding rangeland degradation and assessing long term trends of vegetation change is thus critical to design sustainable management practices. Mongolian rangelands represent about 2.5% of the world’s total grassland area and are considered among the last intact rangelands in the world. Most of the Mongolian territory is covered by rangelands and the livelihoods of nearly half of the Mongolian population are related to livestock grazing on rangelands. The main objectives of this PhD thesis were (1) to compile previous studies on rangeland degradation in Mongolia and systematically review and synthesize information on how studies identified degradation, the theoretical frameworks used, drivers of degradation and the geographical distribution of studies, (2) to detect trends in vegetation change in Mongolian rangelands using broad scale long-term monitoring data, and (3) to investigate the drivers of change in vegetation over ~10 years in the steppe zone of Mongolia using detailed field data. Trends in the literature indicated growing concerns about rangeland degradation in Mongolia, especially since the turn of the 21st century when the number of international scientific publications on this topic considerably increased. However, the lack of a common definition of degradation and of standardized ways of measuring it makes it difficult to compare results of different studies. Using a nationwide long-term database of rangeland health in Mongolia, we detected mostly non-significant trends in key indicators of vegetation change across the forest steppe, steppe and desert steppe. However, where significant trends were detected, these were consistent with reported rangeland degradation. For example, we observed noticeable decreasing trends in grasses characteristic of healthy rangelands, including Stipa sp. This was the first attempt to use the database of the National Rangeland Monitoring program and the results emphasize the value of this national resource. Using detailed field data, we found that changes in vegetation over a ~10-year period were widespread across the steppe. Plant communities changed from communities dominated by grasses toward communities dominated by annuals and sedges that are characteristic of degraded ecosystem states. However, disentangling the role of different drivers remains difficult. Our results highlight the importance of considering regional differences in the effect of different drivers on grassland vegetation when designing sustainable grazing management strategies. In all, this study shows that we are still far from understanding the complexities of rangeland degradation. Nevertheless, current efforts are promising, and Mongolia provides a good example for the world.
Governing land use and restoration: The long-term progress of environmental and agricultural policies on sustainable rangeland management and restoration in Iceland
(2020-06) Petursdottir, Thorunn; Ása L. Aradóttir; Susan Baker; Guðmundur Halldórsson; Faculty of Environmental and Forest Sciences (AUI); Náttúra og skógur (LbhÍ)
Every summer, free-roaming sheep graze large parts of Icelandic rangeland ecosystems, even though some of these rangeland areas are estimated to be in a severely eroded or even collapsed ecological condition. Improved rangeland management and ecosystem restoration of severely degraded rangelands have been designated as official agricultural and environmental policy tasks of the Icelandic government for the last decades. Several new agri-environmental programs and projects have been established since 1990, with the aim of maintaining and improving the ecological condition of rangeland ecosystem and to facilitate behavioral changes among sheep farmers in relation to sustainable rangeland management. Nevertheless, little is known about the overall long-term progress of these activities and their processes and outcomes have never been studied in an interdisciplinary manner. The main aim of this thesis was to carry out research on rangeland management and restoration in Iceland by examining, through a social-ecological lens, if the expected long-term progress of identified policy goals and all related programs and projects has been achieved. The first step of the research was to do a historical analysis on the main drivers of ecological restoration in Iceland during the last century and map if the drivers had changed over time. That study was based on a catalogue of 100 restoration programs, projects and areas of restoration activity (75-85% of all restoration activities in Iceland). The second step included an investigation of the SES surrounding rangeland restoration in Iceland to assess whether social factors, such as stakeholders´ attitude and behavior, influenced the effectiveness of agricultural and environmental policies related to rangeland restoration and improved rangeland management. That study was based on qualitative research, where 15 stakeholders were interviewed. The third step was to examine if a large-scale rangeland restoration program had facilitated expected attitudinal and behavioral changes among the sheep farmers who participated in the program. This step was based on a questionnaire where sheep farmers were asked about their attitude and behavior in relation to rangeland restoration and land management and the replies from participating farmers were compared to the replies from a control group of non-participating farmers. The fourth step was to map the administrative structure that steers rangeland management and explore the governance system’s structure and functions in order to elucidate the policy context in which agricultural and environmental policy targets for improved rangeland management practices were framed. This final study was also based on a questionnaire that was distributed to selected public and semi- public sector employees and sheep farmers. The results were used to gauge the participants’ attitude concerning rangeland management, their perception on state support and level of collaboration related to rangeland restoration and their views on current policies related to rangeland management. The findings from the first step of the research revealed that catastrophic soil erosion, depleting farmlands in the beginning of last century, was an early driver of ecosystem restoration in Iceland. The III findings also showed that soil erosion still ranked high as a driver in the early 2000s, although other drivers, such as moral values and nature conservation, along with concerns about use values, such as in relation to recreation, were also strong motivators for restoration actions. Public policy programmes were found to be a minor driver, which might indicate weaknesses in the policy instruments used for ecological restoration. The findings from the second step of the research showed that social factors, such as attitude and behavior, can be used as indicators of the effectiveness of restoration policies. They also pointed to a lack of functionality in the governance of SESs that could deter progress in achieving policy goals, and possibly block the necessary behavioral change among related stakeholders. Results from the third step showed that the restoration program investigated had not facilitated behavioral change in relation to improved rangeland management among participating farmers compared with non-participants, even though the participating farmers were shown to be more aware of the potential of rangeland restoration and were more motivated to engage in further collaboration, compared to the non-participants. The results also indicated that the direct incentives provided by the program were pushing the participants to favor agronomic instead of ecological approaches in their restoration activities. Furthermore, several organizational errors within the program management were detected, for instance regarding integration of participatory approaches and level of personal connections between the participants and the Soil Conservation Service that might be halting its further progress. Results from the fourth step indicated strongly that neither the governance process nor the current administrative structure of rangeland management had significantly facilitated expected changes in attitude among local authorities or among sheep farmers needed to bring about improved rangeland management practices within the agricultural sector. The key findings of this thesis were that the stated policy objectives of improving the ecological condition of rangeland, including the objectives of current agri-environmental programs and project related to rangeland management, have not yet been fully achieved. The thesis also pointed to the need for improved governance practices, by highlighting that the governance system for rangeland management was structurally limited, suffering from weak vertical and horizontal integration, and not designed to maintain and improve the ecological condition of rangelands’ ecosystems in the context of traditional sheep grazing management practices.
The interaction between native insect herbivores, introduced plant species and climate change in Iceland
(2020-06) Hrafnkelsdóttir, Brynja; Guðmundur Halldórsson; Edda S. Oddsdóttir; Halldór Sverrisson; Faculty of Environmental and Forest Sciences (AUI); Náttúra og skógur (LbhÍ)
Climate warming has had significant effects on insect herbivores in Iceland, including an increased rate of establishment of new species as well as changes in outbreak patterns and distribution of insect herbivores. Many of these herbivores live on trees and shrubs. Concurrent with the onset of a warmer climate around 1990, a distinct host shift occurred in a few native insect species which started to feed on the exotic Nootka lupin (Lupinus nootkatensis), which until then had been free from any significant insect herbivory. Later, as the climate has warmed, many outbreaks of native insect species, primarily the Broom Moth (Ceramica pisi) and Satyr Pug (Eupithecia satyrata), have occurred in lupin fields. Broom Moth distribution and damage on young tree seedlings have also increased recently. The main objectives of this thesis were to study: (1) the effects of climate change on the population dynamics and distribution potential of native herbivores on Nootka lupin, using the Broom Moth as a case study and (2) the effects of insect herbivory on the fitness of the Nootka lupin and exotic trees, using seed production and annual growth as proxies for plant fitness. The effects of climate change on the population dynamics of the Broom Moth were studied in two phases: (1) the effects of warmer winters on pupal survival were studied by freezing pupae in a lab study at different sub-zero treatments and (2) the effects of warmer summers on larval development and pupal size, were studied by: (i) sampling and weighing larvae from lupin fields at different times and local climate during the larval growing season and (ii) weighing larvae just before pupation and after pupation. Additionally, the effects of herbivory intensity on the Nootka lupin seed production (fitness) were studied in a 3‐year field study at two sites at contrasting ages and successional stages, including different manipulated herbivory treatments. Winter temperatures were not found to affect Broom Moth survival as different sub‐zero treatments had no effect on the survival of Broom Moth pupae. The major factor affecting the winter survival of Broom Moth pupae was, however, their autumn weight. Broom Moth larvae growth measurements also showed a significant positive relationship between total growing degree days from the beginning of June and summer larvae just before weight pupation. A significant positive relationship was also found between larval weight just before pupation and pupal weight. Seed production of the Nootka lupin was negatively related to herbivory defoliation, as increased herbivory had a negative effect on the number of flowering stems. These negative effects were also affected by the age (successional stage) of the Nootka lupin, as they were only significant in the older Nootka lupin field. Defoliation by Broom Moth larvae was found to have a negative effect on height growth of Sitka spruce, but no effect on black cottonwood. The results of a feeding study indicated that Broom Moth larvae grow better on Nootka lupin than tree seedlings. The main results from these studies are: (1) Warmer summers, but not warmer winters, have enhanced the III winter survival of Broom Moth pupae and, thereby, both facilitated its recent distribution expansion and its increased population density, which have resulted in intensive outbreaks in Nootka lupin fields in Iceland. The recent increase in population density has, however, also been greatly enhanced by the host shift of the Broom Moth over to the Nootka lupin. (2) This enhanced native insect herbivory may affect the exotic Nootka lupin in Iceland by reducing its seed production, seen as a lower expansion rate from older lupin fields and its competitive success. The effect of this may be reduced invasiveness of the Nootka lupin in Iceland. The causes of the observed host-shift of the native insect herbivores over to the Nootka lupin are discussed and may be related to the adaptation of the lupin to the previously low herbivory environment.

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