Spruce-Fir forests are relicts from the Pleistocene and have migrated back north after the previous warming period as well as up in elevation in the southern Appalachian mountains. This in turn created sky islands of isolated, endemic, and disjunct species. These refugal forests require certain climatic parameters similar to Canada’s boreal mountains but also need additional cloud immersion and precipitation. These forests have experienced stressors in the past, but face continued threats such as air pollution and climate change. Due to limited immigration for the majority of the species on these mountains, a significant number of organisms are at risk of being endangered or extinct. Analyzing the relationships and patterns between species distribution and climatic parameters both in the past and present will help create future prediction maps. These will potentially anticipate where habitat reduction might occur and will benefit management and conservation purposes. The first study will analyze current distributions of Spruce-Fir forests to see which model and variable combination best approximates the unique mountain forests environments. Using the optimal model from the first study, the second study will examine which distributional changes may occur in the future and how these changes compare to paleo-environmental distributions. Anticipated results will show a reduction of habitat in lower peaks with minimal impact at higher peaks based on the known projected trends of cloud ceilings. This research will help with forest and conservation management and will impact a multitude of species that rely on this forest to survive.

La disponibilité en eau exerce un contrôle majeur sur les cycles des nutriments terrestres, à travers ses impacts sur le fonctionnement des plantes et des microorganismes du sol. Les changements de magnitude et de fréquence des épisodes de pluie (c’est-à-dire les régimes de précipitations) prédits par les modèles et associés au changement climatique vont ainsi avoir des conséquences importantes sur le fonctionnement des écosystèmes. Les écosystèmes arides et semi-arides sont particulièrement vulnérables à des changements de régime de précipitations, car ils sont déjà contraints par la disponibilité en eau. Cependant, des systèmes plus tempérés peuvent aussi être soumis à des périodes sèches qui peuvent affecter le fonctionnement plante-sol. Dans la présente thèse, les effets d’un historique de régimes de précipitations contrastés ont été étudiés dans des systèmes sol seul et plante-sol, afin de déterminer dans quelle mesure plusieurs semaines de régime hydrique peuvent moduler la réponse des écosystèmes à une réhumectation lors d’un événement pluvieux important. Premièrement, nous avons évalué les effets de régimes de précipitations contrastés dans des mésocosmes de sol seul, sur les communautés bactériennes et fongiques actives et inactives dans le sol, 2 et 5 jours après réhumectation. Nous avons employé une approche de 18O-SIP (stable isotope probing), en réhumectant le sol avec H218O puis en utilisant la métagénomique ciblée sur les bactéries et champignons du sol. Deuxièmement, nous avons mis en place deux expériences séparées en mésocosmes plante-sol avec couvert de blé. La première expérience sol-plante s’est intéressée à la profondeur de sol. Nous avons évalué les effets de régimes de précipitations contrastés sur le flux de C depuis les plantes vers les microorganismes du sol ainsi que la la réponse des microorganismes à différentes profondeurs de sol (de 0 à 35 cm) en utilisant des approches de traceur isotopiques stables (13C-CO2) et 18O-SIP, respectivement. La deuxième expérience plante-sol a évalué les effets de régimes de précipitations contrastés sur la dynamique temporelle (durant 29h) de la réponse du système plante-sol à la réhumectation. En outre, deux niveaux de fertilisation azotée ont permis de déterminer l’éventuelle modulation de la réponse par la disponibilité en N dans le sol. La réponse des communautés bactériennes et fongiques potentiellement actives dans le sol a été évaluée par métagénomique ciblée. La réponse de cycles biogéochimiques a été évaluée à l’aide de traceurs isotopiques stables (13C-CO2 et 15N- NO3-) pour quantifier le flux de C des plantes vers les microorganismes du sol et déterminer la compétition plantes-microorganismes du sol au cours du temps après réhumectation.Nos résultats ont montré un contrôle du régime de précipitation sur la morphologie et physiologie des plantes, les communautés microbiennes du sol ainsi que sur le cycle de l’azote du sol dans nos systèmes. En particulier, des régimes de précipitations peu fréquentes (cycles de périodes sèches longues suivies de périodes de pluie plus importantes) se sont traduits par une augmentation des potentiels de transformation de l’azote dans le sol et une réduction des stocks d’azote minéral dans le sol. Ceci a façonné l’environnement de la réponse de nos systèmes à la réhumectation, que nous avons évaluée en déterminant les dynamiques du C (couplage plantes-microbes et émissions de CO2 du sol), de l’azote du sol (compétition plantes-microorganismes du sol pour le N et émissions de N2O) et de la composition des communautés microbiennes du sol (bactéries et champignons actifs et potentiellement actifs) après réhumectation (...). / Water availability governs terrestrial nutrient cycles by impacting the functioning of both plants and of soil microorganisms. The predicted changes in precipitation patterns (i.e. the magnitude and frequency of precipitation events) associated with climate change, will thus likely have important consequences on ecosystem functioning. Dry and seasonally dry ecosystems are particularly vulnerable to changes in precipitation patterns, as they are already constrained to a large extent by water availability. However, more mesic systems may also experience dry periods that may impact plant-soil functions. In this thesis, experiments in soil-only systems and plant-soil systems were used to gain insight into how the legacy effects of several weeks of exposure to contrasted precipitation patterns set the scene for the rewetting response of the system. First, in an experiment using soil-only mesocosms, we evaluated the effects of contrasting precipitation regimes on the actively growing as well as the inactive bacterial and fungal communities 2 and 5 days after rewetting, using an 18O-SIP (stable isotope probing) approach by applying H218O followed by metagenomics targeting soil bacteria and fungi. Second, we performed two separate and complementary experiments using plant-soil mesocosms with wheat plant cover. The first plant-soil experiment focused on soil depth. It determined the effects of contrasting precipitation patterns on the flux of C from plants to microbes and the microbial response to rewetting at different soil depths, using a heavy isotope tracer approach (13C-CO2) and 18O-SIP with metagenomics respectively. The second plant-soil experiment evaluated the effects of a history of contrasting precipitation patterns on the dynamics of the rewetting response of the plant-soil system over time (over 29 hours post-rewetting). In addition, two levels of N inputs allowed to determine how N availability modulated plant-soil responses. The response of the potentially active soil bacterial and fungal communities to rewetting was assessed using targeted metagenomics. The responses of biogeochemical cycles were evaluated using heavy isotope tracers (13C-CO2 and 15N-NO3-) to quantify C flux from plants to soil microorganisms and plant-microbial competition for N over time post-rewetting.We found that precipitation patterns shaped plant morphology and physiology, microbial community composition as well as soil N cycling in our systems, which set contrasting scenes for the rewetting responses in our systems. In particular, infrequent precipitation patterns (cycles of longer dry periods followed by larger magnitude rain events) resulted in increased microbial N transformation potentials and smaller inorganic N pools. The rewetting responses were determined by evaluating C dynamics (plant-microbial coupling and soil CO2 efflux rate), N dynamics (plant-microbial competition for N and soil N2O efflux rate) and microbial dynamics (composition of active and potentially active bacterial and fungal communities after rewetting). First, we found that plant-microbial coupling (i.e the microbial assimilation of C from fresh photosynthate) may be reduced under more infrequent precipitation patterns, especially near the soil surface, and under conditions of low N availability. Our findings also suggest that whilst in soil-only systems, dead microbial cells appear to be a major source fuelling soil CO2 efflux pulse upon rewetting, in plant-soil systems root respiration plays an important role in the magnitude of the CO2 efflux upon rewetting. Second, concerning soil N dynamics, we found, in concurrence with previous studies, that soil microorganisms were the stronger competitor for N over short time scales, likely due to their overall fast response rates and high affinity for substrate, whilst plants outcompeted soil microbes for soil N assimilation, over longer time scales likely taking advantage of the fast microbial turnover (...).

In deserts, global environmental changes, plant community structure, and soil water availability form a complex relationship characterized by direct and indirect relationships and feedbacks. Plant community structure is affected by the establishment and spread of invasive grasses, which form a positive feedback with wildfire. Plant community structure is also controlled by top-down trophic interactions by small-mammals and climate change, which alters the timing and amount of soil water. In deserts, soil water availability mediates the effects of global environmental changes and trophic interactions on plant community structure because it is the limiting resource for plant growth. In order to predict future changes in plant community structure, it is critical to understand how climate change, increased wildfire frequency and trophic interactions affect the establishment of invasive grasses and soil water after disturbance. Chapter 1. The objective was to understand the interactive effects of projected changes in climate, secondary wildfire, and rodent-exclusion on plant community structure. Mixed models revealed that all three factors interacted to magnify the establishment of the invasive annual grass B. tectorum in our post-fire experimental plots. In addition, structural equation models revealed that B. tectorum density was negatively correlated with the density of invasive annual forbs the following year, suggesting that B. tectorum competitively excludes other plant species. Chapter 2. The first specific aim was to understand the interactive effects of rodent-exclusion and secondary wildfire on the timing and amount of soil water availability. The second specific aim was to understand how invasive annual grass density controls soil water availability throughout the spring. Bayesian models revealed that rodent-exclusion and secondary wildfire affected soil water availability during specific windows of time throughout both experimental years. The most robust trend occurred in May of both experimental years, when rodent-exclusion, secondary fire plots had significantly less soil water availability than rodent-exclusion, single fire plots. Bayesian models also revealed there was little correlation between invasive grass density and soil water availability throughout the growing season.

The aim of this dissertation was to improve our understanding of the mechanisms underlying biodiversity ecosystem functioning (BEF) relationships and the provisioning of ecosystem functions in temperate forest soils. I studied the role of tree diversity on soil microbial properties, standard litter decomposition, abiotic soil properties, and soil surface temperature. All studies took place in the Kreinitz tree diversity experiment in Central Germany which was established in 2005. It spans a tree diversity gradient from 1 to 6 different commonly cultivated tree species. My experiments included measurements within the whole diversity gradient in November 2017 and a high-resolution time series on monocultures and five-species mixtures in 2017 and 2018. In addition, I utilized tree inventory data about tree mortality, height, diameter and biomass. Chapter I aimed to assess general BEF relationships in soil. Chapter II followed a spatio-temporal framework explaining BEF relationships in forest soils via the spatial and temporal stability of biotic and abiotic properties, based on concepts like species asynchrony and complementarity. Chapter III utilized the perturbation of the extreme summer drought of 2018. It focused on biodiversity-resistance relationships and assessed how tree species richness and identity affected tree mortality rates in the experiment. All three studies showed that tree species identity and community composition are essential in shaping BEF relationships in temperate forest soils and are pivotal for the stable provisioning of ecosystem functions. The influence of tree species identity and community composition could be related to changes in abiotic soil properties and microclimatic conditions (i.e. soil surface temperature). I found evidence that spatio-temporal dynamics are indeed crucial determinants in BEF relationships in forest ecosystems. Overall, my thesis indicated how climate change and other global change factors will likely influence the provisioning and stability of soil ecosystem functions in forest via their intense pressure on tree community composition and the perturbation of spatiotemporal patterns. Overall, this dissertation advanced our mechanistic understanding of BEF relationships in temperate forest soils. While it underlined the dangers of global change for the provisioning of ecosystem functions, it also offered vantage points to prepare our forests for a changing future.

Biodiversity has been heavily impacted by anthropogenic landscape changes associated with natural resource extraction. Terrestrial mammals, which disproportionately maintain ecosystem functions, are among the species most affected by anthropogenic landscape changes. In turn, it is important that we incorporate mammal conservation into natural resource extraction to mitigate biodiversity change, for which we must better understand the dynamics of mammal communities. I used data from motion-activated camera traps deployed in the northwest Nearctic to investigate two aspects of mammal communities: how the environment shapes fine-scale mammal diversity and how mammalian predator species coexist. In my first study, I compared how well natural and anthropogenic landscape features explain fine-scale mammal diversity within and between six variably industrialized landscapes. I found that anthropogenic landscape features explain fine-scale mammal diversity better than natural features in heavily industrialized landscapes, where they may increase or decrease diversity. In my second study, I examined whether prey partitioning facilitates the coexistence of mammalian predator species in an industrialized boreal landscape. My findings suggest that sympatric predator species only partially partition prey, as some predator species had identical prey associations. Strikingly, though, I also found that all predators were positively associated with white-tailed deer, an invasive prey species made abundant by industrial landscape changes. Together, these findings reveal that industrial landscape changes significantly alter both the spatial distributions and predator–prey dynamics of mammal communities. This work can inform conservation and restoration strategies for slowing biodiversity change. / Graduate

Achieving sustainable development to meet the needs of current and future generations is currently on top of the global agenda, both in scientific research as well as global politics. However, achieving sustainable development is still a grand challenge, not least because it is embedded in the context of global change that affects most resource use systems worldwide in multiple ways. Even though many approaches to sustainable management do consider the connection between human activity and environmental dynamics, the role of human behavior as a main driver of system dynamics in coupled human and natural systems is often only poorly addressed. In this thesis, we aim to contribute to an improved understanding under which conditions human resource use decisions lead to sustainable outcomes, with regard to global change. For this, we will take the perspective of human decision-making and its social, ecological and economic consequences in two different resource use contexts, namely a) pastoralism in drylands and b) disaster risk management with respect to floods. We explicitly consider individual human decision-making as driver of social-ecological system dynamics, investigate the feedbacks between system components, as well as the impact of global change on resource use. To analyze such complex system dynamics, simulation models have proven to be helpful analysis tools. Particularly agent-based modeling represents a flexible and powerful analysis tool, as it allows us to model the decisions and interactions of individual agents at the micro level, while at the same time observing the outcome of their behavior on a system level. Within three case studies, we develop agent-based simulation models that capture the dynamics and feedbacks of the social-ecological system under consideration in a spatially explicit way. The first study analyzes the performance of disaster management organizations under change. In the second study, we aim to detect the drivers for polarization in a pastoral system in Morocco. The last study investigates behavioral change of pastoralist households and its impact on social, ecological and economic outcome measures. By analyzing a range of scenarios in each study, we determine both the long-term impact of different decision regimes on the state of the social-ecological system as well as the dimensions of change that have the most profound impact on the system dynamics and the sustainability of resource use. Main results that could be obtained from the modeling experiments include the identification of key resources that have a high influence on the long-term system dynamics. We are also able to show that under the influence of global change, access to certain resources gains in importance, as resources can act as buffer mechanisms to mitigate the adverse effects of global change. Through the operationalization of behavioral theories in model rules and the explicit representation of heterogeneous agent decision making, we could determine under which conditions a more refined representation of human decision making matters, and when a change in behavioral strategies leads to different social-ecological outcomes. Furthermore, all three modeling studies demonstrate the usefulness of stylized agent-based models to gain insights into complex systems. Overall, this thesis contributes to social-ecological systems research by developing appropriate simulation models to address the problem of sustainable resource use under global change.

Flow regime, the magnitude, duration and timing of streamflow, controls the development of floodplain landforms on which riparian vegetation communities assemble. Streamflow scours and deposits sediment, structures floodplain soil moisture dynamics, and transports propagules. Flow regime interacts with environmental gradients like climate, land-use, and biomass-removing disturbance to shape riparian plant distributions across landscapes. These gradients select for groups of riparian plant species with traits that allow them to establish, grow, and reproduce on floodplains – riparian vegetation guilds. Here I ask, what governs the distributions of groups of similar riparian plant species across landscapes? To answer this question, I identify relationships between riparian vegetation guilds and communities and environmental gradients across the American West. In Chapter One, I discuss guild-based classification in the context of community ecology and streams. In Chapter Two, I identified five woody riparian vegetation guilds across the interior Columbia and upper Missouri River Basins, USA, based on species’ traits and morphological attributes. I modeled guild occurrence across environmental gradients, including climate, disturbance, channel form attributes that reflect hydrology, and relationships between guilds. I found guilds’ distributions were related to hydrology, disturbance, and competitive or complementary interactions (niche partitioning) between co-occurring guilds. In Chapter Three, I examine floodplain riparian vegetation across the American West, identifying how hydrology, climate, and floodplain alteration shape riparian vegetation communities and their guilds. I identified eight distinct plant communities ranging from high elevation mixed conifer forests to gallery cottonwood forests to Tamarisk-dominated novel shrublands. I aggregated woody species into four guilds based on their traits and morphological attributes: an evergreen tree guild, a mesoriparian shrub guild, a mesoriparian tree guild, and a drought and hydrologic disturbance tolerant shrub guild. Communities and guilds’ distributions were governed by climate directly, and indirectly as mediated through streamflow. In Chapter Four, I discuss the utility of guild-based assessments of riparian vegetation, current limitations to these approaches, and potential future applications of the riparian vegetation guild concept to floodplain conservation and management. The classification of vegetation into functional trait-based guilds provides a flexible, framework from which to understand riparian biogeography, complementing other models frameworks for riparian vegetation.

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Digital communication advancements are constantly opening up opportunities for businesses to easily expand and collaborate across borders. The Covid-19 pandemic has caused a situation where people have had to work remotely in a virtual setting which forced managers to adapt to a fully remote management approach. This is a single case study investigating how the industrial company Atlas Copco navigated through two global change projects, one executed in a semi-remote setting, and the other executed in a fully remote setting. The remote setting has made it difficult to build trust, and this thesis aims to increase the understanding of trust building in remote global change projects. This is a qualitative, single case study conducted with an abductive research approach. The data has been collected through interviews with representatives from the case company. The empirical findings show that people define trust differently, whether trust is built over time or exists from the start. The various definitions imply that there are consequences if people define trust differently. The thesis also highlights the importance of communication and support activities when building trust and what role the change management team had in this process. Factors affecting trust building are highlighted and mitigating aspects are presented.

Currently, water demands are in continuous growth, which increases the pressure, in quantity and quality, on the available water resources globally. At the same time, the expected reduction of the natural water contributions, due to global change, depicts a new level of uncertainty. In this context, hydrological models are important tools for planning and managing water resources. Its correct application is essential in areas with high levels of water scarcity (arid and semi-arid regions). The southeast of Spain, the field work of this doctoral thesis, presents one of the highest rates of water scarcity and intensive exploitation of water resources in the European and global context. In addition, the frequency and severity of extreme events (floods) in this study region has increased during last decades as a direct consequence of the global change (climate change and land use changes). This doctoral thesis aims to analyse the intrinsic and complete problem of water resources in arid and semi-arid regions, that is, as a need (in case of scarcity and global change) and as a threat (in case of occurrence of extreme events or floods and global change) while studying certain management and adaptation strategies (technologies of wastewater reuse and water desalination) in view of the dual nature of water resources in arid and semi-arid climate areas, in this case in the southeast of Spain. Based on the above mentioned objective, five manuscripts have been performed and published as scientific articles in journals with high impact factor. These papers analyse certain paradigmatic study areas (hydrological basins, aquifers and municipalities) that belong to the southeast of Spain. Main results obtained in the mentioned scientific works can help local authorities responsible for the management and planning of water resources in this region. / Subprograma de Formación de Profesorado Universitario (FPU15/00636). Convocatoria 2015 del Programa Estatal de Promoción del Talento y su Empleabilidad del Ministerio de Educación, Cultura y Deporte.