The boreal forest is confined to the Northern Hemisphere and is the most continuous and extensive forest in the world. In North America boreal forest extends from the Pacific to Atlantic coast spanning over 10° latitude. White spruce (Picea glauca (Moench) Voss), black spruce (P. mariana (Mill.) B.S.P.), and trembling aspen (Populus tremuloides Michx.) are among the dominant tree species. Black spruce and trembling aspen may form pure stands and occupy similar sites as their edaphic amplitudes overlap; however, spruce is rare on water-deficient sites and aspen does not tolerate excess water. Despite many studies conducted in the North American boreal forest, little is known about relationships between the boreal understory vegetation and softwood or hardwood canopy species in different climate regions. Furthermore, the variation in species diversity and succession between the stands dominated by coniferous trees and those dominated by broadleaved trees within the same region is unknown. The objectives of this study are to determine (1) the difference in the species diversity and floristic composition of understory vegetation between black spruce and trembling aspen stands within the same climatic region, and (2) how the species diversity and floristic composition of understory vegetation in each stand type vary with climate, and soil moisture and soil nutrient conditions.

No description available.

East of Lake Winnipeg is what conservationists call the ‘east shore wilderness’ / ‘heart of the boreal.’ The largest contiguous tract of unindustrialized boreal forest on Earth, this area has been the focus of 15 years of discussion and planning in Manitoba. The area is also designated Waabanong Nakaygum, a homeland to the Anishinaabek of this bush-meets-lake region. Waabanong has seen limited access during the industrial period of personal mechanized mobility due to a lack of constructed all-weather roads. However, an older pattern of travel and mobility does exist across the land, for centuries constituting traditional Anishinaabek patterns of land use and trade. As all-weather roads are being constructed along Lake Winnipeg, oral interviews will examine the question: will the older trails remain in the collective culture of the people or shall the north-south cultural and economic flows replace the east-west bush history traced by the rivers that wind through?

Koldioxidhalterna stiger i världen, vilket bidrar till global uppvärmning. Skogen har en viktig roll i klimatarbetet då stora mängder kol finns lagrad i skog och mark. Speciellt mycket kol finns i boreal skog, som bland annat finns i norra Sverige. Idag pågår en debatt huruvida det är mer fördelaktigt att behålla gammal skog som kolsänka, eller avverka den för att ge plats åt yngre träd. Syftet med litteraturstudien var att ge en klargörande bild över hur åldern på boreal skog påverkar ekosystemets kolbalans, genom att undersöka skogens kolupptagningshastighet samt möjlighet till kollagring. Studien visade att äldre skog har ett större totalt kollager, att medelåldrig skog har högst tillväxthastighet (nettoekosystemproduktion, NEP och nettoprimärproduktion, NPP) samt att NEP är negativ de första 10 åren. Studien visade på osäkerhet kring kolupptag i gamla skogar. Flera variabler, såsom substitution, störningar och biologisk mångfald är inte undersökta i studien och behövs tas i beaktning vid beslutsfattande. Trots detta, antyder litteraturstudien att det är fördelaktigt att låta gammal skog stå kvar som kolsänka, eftersom koldioxidutsläppen behöver minska snarast. Ytterligare ett syfte med studien var att kartlägga de missuppfattningar elever, i senare delen av skolan, har gällande kolets kretslopp. Studien visade på missuppfattningar gällande fotosyntes och respiration hos växter, nedbrytarnas roll samt sammanblandning av begrepp. För att åtgärda problemet kan uppgifter göras där atomer följs över olika nivåer, för att sätta processerna i sitt sammanhang. Stort fokus gällande missuppfattningarna ligger på fotosyntes och respiration och inga artiklar hittades gällande exempelvis det snabba, respektive långsamma, kretsloppet. Få studier är gjorda på svenska elever och då svensk kursplan lägger fokus på samband mellan olika nivåer kan missuppfattningarna vara i annorlunda i Sverige. Hur missuppfattningarna ser ut i svensk skola är föremål för vidare forskning. / The amount of carbon dioxide is rising in the atmosphere, which contributes, to global warming. Since large amounts of carbon are stored in forests, forests play an important part the efforts to improve the environment. Boreal forests, found in e.g. the northern part of Sweden, store especially large amounts of carbon. Today it is being debated whether it is more beneficial for the environment to keep old forests as a carbon sink, or to cut them down in order to make room for younger trees. The purpose of this literature study was to clarify how the age of the forest affects the carbon balance of the ecosystem, by examining the forest’s rate of carbon sequestration and capability of carbon storage. The literature study concluded that older forests, in total, store larger amounts of carbon, while middle-aged forests have he highest growth rate (net ecosystem production, NEP, and gross primary production, GPP) and that NEP is negative in the first ten years. The study showed some uncertainty concerning carbon uptake in old forests. Several variables, such as the effects of substitution, disturbances and biodiversity were not examined in this study and need to be further considered before making decisions. However, the literature study suggests that it is more beneficial to leave old forests as a carbon sink, since emissions of carbon dioxide urgently need to be reduced. Another purpose of the study was to examine the misconceptions that students, in the later school years, have regarding the carbon cycle. This study found misconceptions concerning photosynthesis and respiration in plants, the role of decomposers, as well as getting concepts mixed up with one another. To solve this problem, assignments could be designed where atoms are traced between different levels, in order to put the processes in context. A large part of the focus regarding these misconceptions has been on photosynthesis and respiration and no articles were found regarding e.g. the fast; and the slow; carbon cycle. Few studies of Swedish students have been made and since the Swedish curriculum focuses on the relationship between different levels, the misconceptions might be different in Sweden; what these misconceptions could be in Swedish schools is yet to be investigated.

Inland waters receive substantial amounts of organic carbon from adjacent watersheds. Only about half of the carbon exported from inland waters reaches the oceans, while the remainder is lost en route. This thesis identifies flocculation as an important and significant fate of carbon in the boreal landscape. Flocculation reallocates organic carbon from the dissolved state into particles which are prone to settle. Thus, flocculation relocates organic carbon from the water column to the sediment. The dissolved organic carbon (DOC), mainly originating from terrestrial sources, in a set of Swedish lakes was found to determine the extent of sedimentation of particulate organic carbon. A major fraction of the settling particles were of allochthonous origin. This implies that allochthonous DOC was the precursor of the settling matter in these lakes. The gross sedimentation was of the same magnitude as the evasion of carbon dioxide to the atmosphere. Sunlight, especially in the photosynthetically active region, stimulated flocculation of DOC. The effect of light appeared to involve a direct photochemical reaction. Iron was involved in the flocculation but it could not be unravelled whether the iron catalyzes the flocculation or just co-precipitates with the settling matter. Microbial activity was identified as the main regulator of the flocculation rates. Accordingly, alteration of temperature, oxygen concentration and pH did not affect flocculation only indirectly, via their effects on microbial metabolism. A comparison of fluorescence characteristics of organic matter collected in sediment trap and in the sediment surface layer revealed that autochthonous organic carbon was preferentially lost in the sediments while allochthonous matter increased. The recalcitrant nature of the flocculated matter could favour sequestration of this matter in the lake sediment. Hence, the lakes will act as sinks of organic carbon due to a slower mineralization of the flocculated matter in the sediments.

No description available.

The environmental problems facing the world today are largely attributable to anthropogenic activities and landscape change. Addressing these challenges in an evidence-based way requires an understanding of precisely how species and ecosystems are responding to human impacts. Discerning linkages between stressors and their ecological repercussions, and using this to inform conservation, can be challenging due to the complexity and uncertainty of ecological research. I focused on the responses of five wide-ranging large mammal species – gray wolf (Canis lupus), Canada lynx (Lynx canadensis), coyote (Canis latrans), white-tailed deer (Odocoileus virginianus) and moose (Alces alces) – to human footprint (measure of human infrastructure and landscape change), using 12 years (2001-2013) of snowtrack surveys conducted across the boreal forest of Alberta. I explored three key challenges to discerning the linkages between ecological dynamics and management actions. First, I asked whether the direction and magnitude of species responses vary depending on the spatial extent and grain of the study. Second, I asked whether these species respond more strongly to individual footprint features or to the cumulative effects of footprint (measured as total footprint), and whether responses to footprint are consistent across species. Third, I evaluated the utility of thresholds for large mammal management and asked whether there is evidence for consistent threshold responses to total footprint across scales. In addressing the first two questions, I evaluated a set of generalized linear mixed effects models (GLMM) relating the relative abundance of each species to individual and cumulative effects of human footprint, using an information-theoretic approach. I compared the direction of species responses across our regional study area (approximately 400,000 km2) to those reported in previous smaller-extent studies (median 1,525 km2), and compared responses across three spatial grains (250m, 1500m, and 5000m transect buffers). In addressing the third question, I conducted a review on the utility of ecological thresholds, described as abrupt changes in the response to a continuous driver, for large mammal management. I further tested for thresholds in species responses to total footprint by comparing linear models (logistic regression) to piecewise regression models. I compared threshold values between two grains (approximately 33km2 - 1500m transect buffer, and 5500km2 - grouping transects into clusters), and across four regions (boreal forest extent, three landscape planning units). I found that the direction of species responses varied with spatial extent, but not grain, and that species responded strongly to a broad suite of footprint features, indicating the need to manage for cumulative effects. Despite the appeal of ecological thresholds, using these as targets is challenging and the success of doing so has rarely been evaluated. I found threshold models to be better supported than linear ones across species, but due to variability and uncertainty in threshold values, the results are more suited as guidelines or hypotheses to be further tested, as opposed to specific management targets. Translating research on complex ecological systems into management actions is a continuing challenge, yet, ongoing biodiversity monitoring and adaptive management may refine our existing tools, and ultimately lead to better environmental stewardship. / Graduate / 2017-09-05 / 0329

The understanding of how different parts of a landscape contribute to streamflow by storing and releasing water has long been a central issue in hydrology. Knowledge about what controls streamflow dynamics across landscapes can further our understanding of how catchments store and release water, facilitate predictions for ungauged catchments, and improve the management of water quality and resources. This thesis makes use of data from the Krycklan catchment in northern Sweden. Streamflow data from 14 catchments (0.12 - 68 km2) with variable landscape characteristics such as topography, vegetation, wetland cover, glacial till soils and deeper sediment soils were used to investigate spatial patterns and controls on runoff. The differences in specific discharge (discharge per unit catchment area) between nearby catchments were large at the annual scale, and have the same magnitude as predicted effects of a century of climate change or the observed effects of major forestry operations. This variability is important to consider when studying the effects of climate change and land use changes on streamflow, as well as for our understanding of geochemical mass balances. Streamflow from different catchments was strongly related to landscape characteristics. The distribution of wetland areas had a particularly strong influence, with an annual specific discharge 40-80% higher than catchments with high tree volume on till soils. During drier periods, catchments with deeper sediment soils at the lower elevations of Krycklan had a higher base flow compared to both forested till and wetland catchments. This pattern was reversed at high flows. The storages releasing water to streams in downstream sediment areas were able to maintain base flow for longer periods and were less influenced by evapotranspiration compared to the more superficial till and wetland systems. The results of this thesis have led to a better understanding of the landscape wide patterns of streamflow during different seasons and time scales. The strong associations to landscape characteristics and variable spatial patterns with season and antecedent conditions form the basis for a conceptual understanding of the processes and spatial patterns that shape the heterogeneity of streamflow responses in boreal catchments. / Hur olika delar av landskapet påverkar vattenbalansen och bidrar till avrinning har länge varit en central fråga inom hydrologin. Kunskap om vad som styr avrinningsdynamiken i ett landskap kan öka vår förståelse av hur olika delar av landskapet bidrar till avrinning, hur avrinningsområden lagrar vatten och bildar avrinning, underlätta prognoser för avrinningsområden utan vattenföringsmätningar och förbättra hanteringen av vattenkvaliteten och vattenresurser. Denna avhandling använder data från Krycklans avrinningsområde i norra Sverige. Vattenföringsdata från 14 delavrinningsområden (0.12 - 68 km2) med olika landskapskarakteristik såsom topografi, vegetation och jordarter, användes för att undersöka rumsliga mönster hos avrinningen över olika tidsperioder samt hur landskapet påverkar variabiliteten. Skillnaderna i specifik avrinning (avrinning per areaenhet) mellan närliggande avrinningsområden var stor för årliga värden, och är i samma storleksordning som effekterna av stora skogsavverkningar samt av förutspådda effekter av det kommande seklets förväntade klimatförändringar. Denna variation är viktig att ta hänsyn till när man studerar hur klimatförändringar och ändrad markanvändning påverkar avrinningen, liksom för vår förståelse av geokemiska massbalanser. Avrinning från olika områden var starkt relaterad till deras landskapsegenskaper. Förekomsten av våtmarker hade ett särskilt starkt inflytande. Områden med en stor andel våtmarker hade 40-80% högre årlig specifik avrinning än områden med hög trädvolym på moränjordar. Under torrare perioder hade områden med djupare sedimentjordar hög avrinning jämfört med både områden med skog på morän och med våtmarker. Under höga flöden var detta mönster omvänt. De vattenlager som bidrar till avrinning i sedimentområden kan upprätthålla basflöde under längre tidsperioder och påverkas mindre av evapotranspirationen än de ytligare flödessystemen i morän och våtmarker. Avhandlingen har givit en bättre förståelse av avrinningens rumsliga variation under olika årstider och i olika tidsskalor. Det starka sambandet mellan landskapskarakteristik och avrinningens varierande mönster under olika årstider och lagringsförhållanden utgör en grund för en begreppsmässig förståelse av de processer och rumsliga mönster som skapar heterogeniteten i flödesrespons i boreala områden.

Afin de mieux appréhender l’ouverture actuelle de la forêt boréale au nord du Québec et d’identifier les facteurs qui en sont responsables, cette thèse a étudié la dynamique, la stabilité et la résilience des deux types d’écosystèmes forestiers en jeu dans la zone de transition, au cours du temps. Ces écosystèmes, les pessières à mousses, denses, et les pessières à lichens, beaucoup moins denses (dites « ouvertes »), partagent la même espèce ligneuse dominante (Picea mariana). La thèse s’est concentrée sur le développement d’outils géochimiques innovants en paléoécologie permettant de retracer la structure et la composition présentes et passées des écosystèmes terrestres, puis sur la reconstruction du régime des feux par analyses de charbons. Elle démontre dans un premier temps que les deux écosystèmes ont des sols aux propriétés physico-chimiques distinctes, et sont entretenus par les interactions sol-végétation-climat. Le deuxième volet montre que les enregistrements chimiques sont également différents dans les sédiments récents de lacs d’étude, selon s’ils sont entourés de pessières à mousses ou à lichens. Grâce aux proxys géochimiques calibrés, le troisième chapitre reconstruit l’histoire de la végétation et des feux au cours de l’Holocène. Il met en évidence une rupture majeure dans la structure des écosystèmes, observée vers 4500-4000 ans calibrés avant présent, et permet de conclure à une ouverture de la forêt boréale à cette période en raison d’une augmentation de la fréquence de feux. La stabilité précaire des états actuels est mise en perspective avec le contexte présent d’augmentation des feux dans la région et les mesures d’aménagement à adapter en conséquence. / In order to better figure out the ongoing transition of the boreal forest in northern Quebec and to identify the responsible factors, this thesis studied the dynamics, stability and resilience of the two forest ecosystems at stake, over time. These ecosystems, the closed-canopy dense moss forest and the open lichen woodland, share the same dominant tree species (black spruce, Picea mariana). The thesis focused on the development of innovative geochemical tools in palaeoecological studies that could track present and past terrestrial ecosystem structure and composition, and then focused on the reconstruction of past fire regimes through lacustrine charcoal analyses. A first step demonstrated that the soils of both ecosystems displayed distinct physical and chemical properties and are maintained by the feedback interactions in the soil-vegetation-climate system. The second step showed that modern sediments of study lakes recorded variations in their chemical composition depending on whether they were surrounded by moss forest or lichen woodland. Using the so calibrated geochemical proxies, the third chapter reconstructed the vegetation and fire histories during the Holocene. A major disruption in ecosystem structure was evidenced 4500-4000 years calibrated before present and led to the conclusion of a boreal forest opening at that time due to an increase in fire frequency. The precariousness of the present states stability is discussed in light with the current context of fire increase in the study region and suggests that forest management should be adapted consequently.

Le feu est la principale perturbation en forêt boréale mixte. La sévérité des feux n'est pas spatialement homogène et épargne souvent partiellement ou entièrement des parties de la forêt appelées îlots résiduels. Ces îlots forestiers résiduels après feux sont étudiés depuis de nombreuses années, et ces études se sont surtout intéressées aux facteurs déterminant leur occurrence à l'échelle du paysage. Cependant, les travaux réalisés en Fennoscandinavie et aux États-Unis ont révélé la présence de peuplements forestiers (appelés refuges) ayant la capacité de se maintenir dans le territoire pendant plusieurs millénaires. L'objectif principal de cette thèse était de caractériser la dynamique temporelle et la structuration d'îlots forestiers localisés au sein de la forêt boréale mixte de l'est du Canada. Treize îlots forestiers qui ont échappé au dernier feu ont été échantillonnés. Des carottes de sols ont été extraites dans chacun des sites pour réaliser des analyses paléoécologiques (charbons et macrorestes). Les caractéristiques stationnelles de chaque site ont été échantillonnées pour déterminer si les refuges se distinguent des autres îlots résiduels. La charge en combustible des îlots a également été mesurée. Les données ont également servi à alimenter des modèles numériques de comportement du feu (Fire Behavior Prediction System, BehavePlus, FlamMap3) qui ont été utilisés afin de déterminer les caractéristiques stationnelles qui permettent aux refuges d'échapper au feu de façon récurrente. Les résultats ont mis en évidence l'existence de deux types d'îlots résiduels en forêt boréale mixte : les refuges et les autres îlots résiduels. Les refuges sont moins susceptibles au feu comparativement aux îlots résiduels qui ont échappé uniquement au dernier feu, probablement de façon fortuite. Les refuges ont en revanche la capacité de persister dans le paysage forestier durant plusieurs millénaires, ne brûlant uniquement durant des feux particulièrement sévères. Les analyses macrofossiles des refuges soulignent des changements majeurs au sein de la végétation locale, avec comme événement remarquable le passage de formations dominées par Larix laricina/Picea sp. vers des formations dominées par Abies balsamea/Thuja occidentalis. Ce changement de végétation s'est produit à différentes périodes selon les sites, soulignant un processus endogène dans cette transformation de la végétation. Le développement de Larix laricina s'est accompagné dans certains assemblages macrofossiles de taxons typiques de milieux humides (tels que les characées). L'importante couche de matière organique qui caractérise les refuges semble entraver le développement d'espèces de début de succession telles que Betula papyrifera et Populus tremuloïdes. Les îlots refuges doivent leur persistance dans le paysage forestier à un certain nombre de facteurs biotiques et abiotiques qui limitent le passage du feu. Les résultats issus des simulations du comportement du feu, suggèrent un rôle mineur des coupe-feu (lacs, tourbières, et monticules rocheux essentiellement), de la charge en combustible et de la topographie dans l'occurrence des refuges. L'humidité semble être le seul facteur déterminant leur développement au sein de la mosaïque paysagère. Les refuges se mettent en place au sein de faibles dépressions humides qui favorisent l'accumulation de la matière organique. La structure des refuges et des autres îlots résiduels révèle deux principales caractéristiques permettant de les distinguer sur le terrain : le diamètre moyen des arbres et l'épaisseur de la matière organique. Les arbres des refuges ont un plus petit diamètre que ceux des autres îlots résiduels. L'importante épaisseur de la matière organique des refuges affecte négativement la croissance des arbres. Ces caractéristiques pourront être utilisées comme outils d'aide à la décision dans les stratégies d'aménagement forestier. / Fire is the main natural disturbance shaping boreal forest landscapes. In North American boreal ecosystems, wildfires contribute to the creation of a complex mosaic of stands of varying age, composition, and structure, within which other disturbances and processes can interact. A burned area usually includes tree patches that partially or entirely escaped fire, called post-fire residual patches. The spatially occurrence of post-fire residual patches has been extensively described. However, the presence of fire refuges has been reported in Fennoscandia and in United-States, which can escape fire for several millennia. The aim of this study was to characterize temporal dynamics in post fire residual patches in mixedwood boreal forest of eastern Canada. The analyses concern the reconstruction of fire and forest dynamics history though Holocene and identify characteristics features of these patches. This research aimed to contribute significantly to the objectives of ecosystemic management to preserve biological diversity in the forest mosaics.Thirteen post-fire residual patches which escaped the last fire have been sampled. At each stand, cores and monoliths were extracted for paleoecological analyses. The reconstitution of fire history and forest dynamics were studies by using macroscopic charcoals and macroremains. The characteristics features of stands were also sampled, to differentiate fire refuges from other post-fire residual patches. The fuel load was also measured, and all these data were used as inputs for fire behavior modeling (Fire Behavior Prediction System, BehavePlus, FlamMap3), to identify stand characteristics prevent fire refuges to burn in comparison with other residual stands and forest matrix.The results showed the presence in the landscaped of two types of post-fire residual patches in mixedwood boreal forest: fire refuges and other post-fire residual patches. The fire refuges present less fire susceptibility than other post-fire residual patches, which escape only the last fire probably by chance. On the other hand, fire refuges can persist in the landscape for several millennia, burning in the most severe fires. The forest dynamics reconstruction in fire refuges, highlight major shift in the vegetation from Larix laricina/Picea sp. to late successional species Abies balsamea/Thuja occidentalis. Occuring at all stands, but at different periods of Holocene, these changes can be attributed to internal processes. The presence of Larix laricina was associated to the occurrence of aquatic taxa (e.g. Characear). The late successional species (Abies balsamea/Thuja occidentalis) can persist in the landscape for several centuries due to moisture conditions. The thickness of organic matter recorded in fire refuges seems to inhibit the recruitment of early successional species such as Betula papyrifera et Populus tremuloïdes.The fire refuges owe their persistence in the landscape to abiotoc and biotic factors that limit fire occurrence. Then results obtained from fire behavior simulations, suggest a minor role of fire breaks (lakes, rocks), fuel load and topography in persistence of fire refuges. Local moisture condition seems to be key factor in their occurrence in the landscape. The fire refuges occur likely in depressions, which favor organic matter accumulation. The structure of fire refuges and other residual patches revealed two main characteristics, which distinguish between the two types of residual patches: Mean diameter of trees and thickness of organic matter. The trees of fire refuges present smaller tree diameter than other post-fire residual patches. The thickness of organic matter accumulation in fire refuges affects negatively the growth of trees. These features can be used as tools for decision support in forest management strategies.