The objective of this thesis is to evaluate the ecological consequences of buffer strip retention on riparian and terrestrial biodiversity. Earlier studies on forest buffer strips have evaluated their effectiveness in relation to water quality and aquatic biota. However, forests along streams are species rich habitats for many organism groups. Buffer strip management is assumed to be important also for protecting such species. Current approaches to biodiversity-oriented forest management practices need to be scientifically evaluated. In this thesis the effects on bryophytes and land snails have been evaluated. A before-and-after experiment along 15 small streams in northern Sweden showed that buffer strips of 10 m on each side of the stream moderated the negative effects exhibited at the clear-cuts. The number of land snail species remained similar as to before logging and the number of vanished bryophyte species was lower in the buffer strips than in the clear-cuts. The ground moisture influenced the survival rate of land snails at the clear-cuts. At mesic sites many species vanished but at wet sites the snail fauna was unaffected by the logging. Many bryophyte species, most of them liverworts, decreased or disappeared in the buffer strips. These were mostly growing on substrates elevated from the forest floor, such as logs, stumps and tree-bases. A number of nationally red-listed species, sensitive for changes in microclimate, were among those decreasing most. Thus, for the species in most need of protection the buffer strips were too narrow. An experiment with bryophyte transplants followed over a season showed that wet ground moisture moderated the negative edge effects in narrow buffer strips. On the other hand, the growth in mesic and moist sites was almost as low as in comparable clear-cuts. Microclimatic edge effects are stronger at south facing than north-facing edges of forest clear-cuts. This was shown in an experiment using bryophyte growth as an indicator of differences in microclimate. However, the depth of edge influence seemed to be similar between north- and south-facing forest edges, >30 m for one species. An explanation for this could be that wind penetrates deeper into edges than solar radiation and has a more variable direction. In conclusion, narrow buffer strips consist entirely of edge habitat. For many species the environment in buffer strips is good enough for persistence. For others, most notably bryophyte species on convex substrates, wider buffer strips are needed to ensure long-term survival.

The presented thesis investigates the role of bryophytes in the deadwood and carbon (C) cycle of boreal black spruce forests in Labrador, Canada. All major forest C pools (live-tree, standing and downed deadwood, organic layer, mineral soil) were quantified for three old-growth, nine clearcut harvested, and three burned forest stands in order to characterize forest C dynamics of a high-latitude humid boreal forest ecosystem. Tree and aboveground deadwood C dynamics of Labrador black spruce forests were similar to those of drier or warmer boreal forests. However, due to bryophyte-driven processes such as woody debris (WD) burial and paludification, the studied forests contained high organic layer, mineral soil, and buried wood C stocks. The comprehensive field-measured data on C stocks was used to evaluate the CBM-CFS3, a Canadian national-scale C budget model, with respect to its applicability to Labrador black spruce and humid boreal forests elsewhere. After selected biomass estimation and deadwood decay parameters had been adjusted, the CBM-CFS3 represented measured live-tree and aboveground deadwood C dynamics well. The CBM-CFS3 was initially designed for well-drained upland forests and does not reflect processes associated with bryophytes and high forest floor moisture content, thus not capturing the large amounts of buried wood and mineral soil C observed in the studied forests. Suggestions are made for structural changes to the CBM-CFS3 and other forest ecosystem C models to more adequately represent the bryophyte-regulated accumulation of buried wood, organic layer, and mineral soil C. Accuracy of forest C models could be further improved by differentiating WD decomposition rates by disturbance history, because WD respiration reflects disturbance-induced changes in temperature and moisture regimes. In Labrador, WD respiration was limited by low WD moisture levels and high temperatures in burned stands, and by high WD moisture contents and low temperatures in old-growth stands. Following harvesting, residual vegetation prevents the desiccation of WD, resulting in significantly higher WD respiration compared to old-growth and burned stands. Moreover, the bryophyte layer recovers faster following harvest than following fire, which reduces WD desiccation due to moisture retention, water transfer, and moisture-induced cooling and results in higher WD decomposition rates. Bryophytes are thus a key driver of the deadwood and C cycle of humid boreal Labrador black spruce forests. The author recommends to classify these and similar boreal forests as a functional ecosystem group called “humid boreal forests”, preliminarily defined as “boreal forest ecosystems featuring a bryophyte-dominated ground vegetation layer associated with low soil temperatures, high moisture levels, low dead organic matter decomposition rates, and subsequently (in the absence of stand-replacing disturbances) an accumulation of buried wood embedded in a thick organic layer”. Bryophytes are also an integral component of many coniferous forests outside the boreal biome. Bryophyte-regulated processes such as WD burial or paludification are thus likely significant to the global C cycle. The potential climate change-induced release of large amounts of CO2 from buried wood and soil C pools necessitates an increased understanding of how bryophyte productivity and decomposition constraints will change with increasing temperature and varying moisture regimes. Ecosystems such as humid boreal forests with potentially high C losses to the atmosphere may thus be identified and counteractive forest management strategies can be developed and implemented. / Cette thèse de doctorat s’intéresse à l’influence qu’exercent les mousses sur les cycles du bois mort et du carbone (C) dans des pessières noires boréales humides du Labrador, Canada. Toutes les réservoirs majeurs de C (arbres vivants, bois mort sur pied et effondré, l’horizon de matière organique, sol minéral) de trois pessières vierges, neuf coupes à blanc et de trois pessières brûlées ont été quantifiés pour caractériser le cycle du C des forêts humides boréales du nord. Les dynamismes de C des arbres vivants et du bois mort supraterrestre ressemblaient à ceux des forêts boréales plus sèches ou aux températures plus chaudes. À cause des processus régulés par les mousses (l’enterrement du bois mort ou la paludification), les forêts étudiées contenaient des stocks élevés de C au sein de l’horizon de matière organique, le sol minéral et le bois enterré. Les données ont aussi été utilisées pour évaluer le MBC-SFC3, un modèle national canadien du bilan du C, concernant son applicabilité aux pessières boréales humides de Labrador et d’ailleurs. Suite à l’ajustement de quelques paramètres, p.ex. des taux de décomposition, le MBC-SFC3 reproduisait bien le dynamisme mesuré des arbres vivants et du bois mort supraterrestre. Le MBC-SFC3 a initialement été développé pour les sites bien drainés et ne considère pas les processus associés avec les mousses ou l’humidité élevée du sol. Conséquemment, le MBC-SFC3 ne représentait pas les stocks élevés de C mesurés pour le bois enterré et pour le sol. Les modifications structurelles du MBC-SFC3 et d’autres modèles du C forestier sont nécessaires pour représenter adéquatement l’accumulation du C au sein de ces réservoirs. La précision des modèles du C forestier pourrait encore être améliorée par une différenciation des taux de décomposition selon le régime de perturbations, parce que la respiration du bois mort reflète les changements de la température et d’humidité associés avec une perturbation spécifique. Dans les pessières brûlés du Labrador, la respiration du bois mort était limitée par a faible humidité du bois et des températures élevées; dans les pessières vierges, par l’humidité élevée du bois et des températures basses. Dans les coupes à blanc, la végétation résiduelle empêchait le dessèchement du bois mort. Il s’y ensuivit que la respiration du bois mort y est nettement plus élevée en comparaison avec des pessières brûlés ou vierges. La décomposition du bois mort après coupe à blanc est aussi favorisée par la récupération plus rapide de la couche de mousses, diminuant conséquemment le dessèchement du bois mort par la conservation d’humidité, les transports vertical et horizontale d’eau et le refroidissement induit par l’humidité. Ainsi, les mousses sont les facteurs clés dans les cycles du bois mort et du C des pessières noires boréales au Labrador. L’auteur préconise la classification de ces pessières et des forêts semblables comme un groupe fonctionnel d’écosystèmes nommé : « pessières boréales humides » ; provisoirement définies comme « des écosystèmes forestiers avec une végétation terrestre dominée par les mousses et par conséquent associée avec des températures basses du sol, une humidité élevée, des taux de décomposition faibles et (en l’absence de perturbations) l’accumulation du bois enterré dans des couches organiques epaisses ». En outre, les mousses sont des éléments principaux des nombreuses forêts résineuses n’appartenant pas au biome boréal. Les processus régulés par les mousses tels l’enterrement du bois mort ou la paludification sont probablement importants pour le cycle global de C. La libération potentielle de grandes quantités de CO2 des réservoirs « bois enterré » et « sol » à la suite des changements climatiques exige une meilleure compréhension des transformations de la productivité des mousses et des limitations de la décomposition dues aux températures plus élevées et au taux d’humidités variables. Ainsi, les écosystèmes aux pertes potentielles de C élevées (p.ex. les pessières boréales humides) peuvent être identifiés et des mesures d’aménagement antagonistes peuvent être développées et implémentées. Traduction assistée par : Karl-Heinrich von Bothmer, Géry van der Kelen / Die vorliegende Arbeit untersucht die Einflüsse von Moosen auf den Totholz- und Kohlenstoff-(C)-Kreislauf in borealen Schwarzfichtenwäldern in Labrador, Kanada. Um den C-Kreislauf dieses humiden borealen Waldökosystems zu charakterisieren, wurden alle bedeutenden C-Speicher (lebende Bäume, stehendes und liegendes Totholz, organische Auflage, Mineralboden) von drei Primärwald-, neun Kahlschlags- und drei Brandflächen quantifiziert. Die C-Dynamiken der Bäume und des oberiridischen Totholzes der Untersuchungsflächen ähnelten denen von trockeneren und/oder wärmeren borealen Wäldern, während die organische Auflage, der Mineralboden und das begrabene Totholz bedingt durch von Moosen regulierte Prozesse wie Totholzeinlagerung und Paludifizierung besonders hohe C-Vorräte aufwiesen. Mit dem umfangreichen C-Datensatz wurde das CBM-CFS3, das nationale kanadische C-Modell, am Beispiel Labradors im Hinblick auf seine Anwendbarkeit in humiden borealen Wäldern evaluiert. Nach Anpassung ausgewählter Parameter, z.B. der Totholzabbauraten, wurden die gemessenen C-Dynamiken der Bäume und des oberiridischen Totholzes vom Modell abgebildet. Das CBM-CFS3 wurde ursprünglich für staunässefreie, terrestrische Waldstandorte entwickelt und berücksichtigt keine mit Moosen oder hoher Bodenfeuchte assoziierten Prozesse, so dass es die hohen C-Vorräte des begrabenen Totholzes und des Bodens nicht widerspiegelte. Eine adäquate Abbildung der Akkumulation von C in diesen Speichern erfordert strukturelle Änderungen des CBM-CFS3 und anderer Wald-C-Modelle. Die Genauigkeit von Wald-C-Modellen könnte darüber hinaus durch eine Differenzierung der Totholzabbauraten in Abhängigkeit vom Störungsregime verbessert werden, da störungsspezifische Veränderungen von Temperatur und Feuchte von der Totholzatmung widergespiegelt werden. Im Untersuchungsgebiet limitierten geringe Holzfeuchten und hohe Holztemperaturen die Totholzatmung auf Brandflächen. In Primärwäldern wirkten dagegen hohe Holzfeuchten und geringe Holztemperaturen hemmend. Auf Kahlschlägen verhinderte die verbleibende Vegetation die Austrockung des Totholzes, was zu signifikant erhöhten Atmungsraten im Vergleich zu Brand- und Primärwaldflächen führte. Zudem wird der Totholzabbau auf Kahlschlen durch eine schnellere Erholung der Moosdecke als auf Brandflächen gefördert, da Moose durch ihr hohes Wasserspeichervermögen, vertikalen und horizontalen Wassertransport und feuchte-induzierte Kühlung der Austrockung des Totholzes entgegenwirken. Moose sind somit ein Schlüsselfaktor im Totholz- und C-Kreislauf der humiden borealen Schwarzfichtenwälder Labradors. Die Autorin empfiehlt die Klassifikation dieser und ähnlicher borealer Wälder als eine funktionelle Ökosystemgruppe namens “humid boreal forests”; vorläufig definiert als “boreale Waldökosysteme mit durch Moose dominierter Bodenvegetation und damit assoziierten niedrigen Bodentemperaturen, hohen Bodenfeuchten, geringen Abbauraten und (in Abwesenheit großflächiger Störungen) der Akkumulation von begrabenem Totholz in mächtigen organischen Auflagen”. Auch außerhalb des borealen Bioms sind Moose ein wesentlicher Bestandteil vieler Nadelwälder. Durch Moose regulierte Prozesse wie Totholzeinlagerung und Paludifizierung sind daher wahrscheinlich relevant für den globalen C-Kreislauf. Die durch den Klimawandel bedingte potentielle Freisetzung von großen Mengen CO2 aus begrabenem Totholz und dem Boden macht ein besseres Verständnis der zu erwartenden Veränderungen von Mooswachstum und Abbauhemmnissen als Folge erhöhter Temperaturen und variabler Feuchteverhältnisse erforderlich. Somit können Ökosysteme mit potentiell hohen C-Verlusten, wie z.B. humide boreale Wälder, identifiziert und diesen entgegenwirkende Bewirtschaftungsmaßnahmen entwickelt und umgesetzt werden.

Pure Sn and Sn-alloys are widely used in electrical and microelectronic devices as protective layer to prevent oxidation of Cu conductors and also as a component of Pb-free, Sn-based solders. Sn coatings, typically 0.5-10 μm thick, deposited on substrates, e.g., Cu, brass, etc., are prone to spontaneous growth (i.e., without any external stimuli) of Sn whiskers under ambient conditions. The growth of whiskers from Sn plating has caused numerous failures in micro-electronic devices, mainly due to short-circuiting, leading to failure of components or devices. Whisker growth is, thus especially very critical in aviation, space and defines applications, where the electronic components are designed for longer life span. Furthermore, due to miniaturization of electronic devices, the spacing between adjacent conductors or interconnects can be as small as a few hundred nanometres to a few micrometres, making them more prone to whisker induced short-circuiting. Minor alloying of Sn with Pub was the principle way for mitigating the whisker growth in Sn plated components; however, due to the recent worldwide acceptance of European Union’s Restriction of Hazardous Substances (RoHS) act, enforcing Pub-free manufacturing, whisker growth has re-emerged as a reliability issue in Pub-free solders and the Sn plating finishes. Even after decades of research, a universal whisker growth mechanism and hence effective mitigation technique is still not available in the public domain. This is mainly due to the fact that large number of factors that affect the whisker growth directly or indirectly, making it difficult to devise an experimental procedure, which allows studying effect of one factor at a time while keeping other factors constant. Although many mechanistic models for Sn whispering have been proposed in the past, the experimental evidences to support them are lacking. For example, recrystallization of whisker grain was proposed by various researchers; however, a direct observation confirming whisker grain is indeed a recrystallized grain has never been reported. Nevertheless, it is well understood that whisker growth is a form of stress relaxation process and diffusion plays important role in the formation of whiskers. Since Sn is extremely anisotropic with tetragonal crystal structure, the stress state of Sn coatings, as well as the diffusion needed for mass transport of atoms, varies drastically depending upon the direction of interest. Therefore, it is important to study the role of crystallographic texture (both macroscopic and microscopic) on whisker propensity by systematically varying the crystallographic texture of Sn coating while keeping thickness, grain size, substrate material, and post-deposition storage conditions the same. Better understanding of role of macro- and micro- texture is very crucial before any whispering mechanism can be proposed. Furthermore, recent studies indicate that role of stresses in Sn coatings driving whisker growth is not fully understood. It is generally accepted that compressive stress in Sn coating is the main factor that drives the whisker growth. However, whiskers were also observed when Sn coating was under tensile stress, making the role of stress controversial. Again, the stresses in Sn have multiple origins and need a systematic approach to understand their origin, quantify them and then relate it to whisker growth. Such systematic approach was never adopted in previous works. Hence, the current thesis aims to address the role of macro- and micro- crystallographic texture, stress regeneration mechanism, nature (i.e., magnitude and sign) of stress and stress gradient in the Sn coatings via systematic variation of texture, post-deposition storage conditions and substrate composition, including deposition of an interlayer in between Sn coating and the brass or Cu substrate. Whisker growth was studied from electro-deposited Sn coatings. The deposition parameters were optimized for producing different thickness and grain orientations. X-Ray diffraction (XRD) techniques were used to extract macro-texture of the coatings. The macro-texture measurement using XRD and micro-texture measurement using electron backscatter diffraction (EBSD) showed the same dominant and the second dominant orientations. It was observed that current density and deposition temperature, which are the two main electro-deposition parameters, significantly influence the crystallographic orientation of the grains. Thus, the global or macro-texture can be manipulated by changing the deposition parameters systematically. It was observed that whisker propensity increases drastically by growth of low index planes, such as (100) and (110), during deposition. Hence, proper selection of deposition parameters that lead to growth of high index planes can be used to suppress the whisker growth. Furthermore, micro-texture surrounding whisker grain was studied using EBSD technique by observing the same set of grains surrounding a whisker grain before and after whispering. Orientation imaging microscopy (OIM) maps of several whisker regions clearly indicate that whiskers preferentially grow from low index planes, such as (100), etc. Furthermore, using orientation dependent stiffness mapping (in-plane and out-of-plane), it was noticed that whiskers preferentially grew from regions of soft oriented grains (low modulus) surrounded by hard orientations. In addition, grain boundary disorientation analysis revealed presence of high fraction of high angle grain boundaries (HAGBs) in the vicinity of whisker grain. It was observed that overall fraction of HAGBs in the whispering region was 0.7 while the fraction of HAGBs surrounding and leading to whisker grain was 0.85. In addition, it was observed that whisker grew from pre-existing grain and not from the recrystallized grain. Also, grain boundary sliding was not observed as a pre-requisite for whisker growth in Sn coatings on brass substrate. The local stress field around the whisker grain also plays a crucial role in whisker growth. Therefore, local stress field around whisker site was simulated using crystal plasticity simulation by incorporating grid resolved spatial description of orientation in terms of Euler’s angles. The crystal plasticity model included slip systems of Sn and other material parameters, such as anisotropic elastic stiffness constants, critical resolved shear stresses for different slip systems, etc. Thus, the slip in individual grain was accounted following homogenization to maintain compatibility at grain boundaries. The simulated stress field shows that both in-plane and out-of-plane stresses were highly inhomogeneous without any unique condition around whisker grain. It has been observed that high compressive hydrostatic stresses develop in the vicinity of the whisker grain, while whisker grain is slightly tensile. Therefore, the gradient of hydrostatic stress around the whisker suggests whisker growth is mainly controlled by vacancy transport phenomenon. The stress in Sn coatings may originate from many factors, such as residual stress inherent to electro-deposition, diffusion of substrate atoms (Cu, Zn, etc.) into the coating, formation of interfacial intermetallic compound (IMC) layer, segregation of impurities at Sn grain boundaries, formation of surface oxide layer, and coefficient of thermal expansion (CTE) mismatch between in Sn and substrate as well as between differently orientated grains of Sn. Therefore, it is important to understand the dominant stress regeneration mechanism responsible for whisker growth. To identify dominant mechanism, which can continuously regenerate the compressive stress in Sn, samples deposited under fixed electro-deposition conditions were exposed to different post-deposition storage conditions, such as isothermal aging at room temperature, 50 °C, 150 °C, and thermal cycling from -25 to 85 °C with and without hold time at the highest temperature. It has been observed that Cu6Sn5 IMC growth due to the inter-diffusion of Cu and Sn atoms is the dominant mechanism responsible for whisker growth. Both growth kinetics and morphology of IMC have a significant impact on whisker growth. The role of CTE mismatch in regenerating compressive stresses in Sn coatings on brass substrate for whisker growth is highly limited. The substrate composition as well as the under layer metallization affects the inter-diffusion between Sn and the substrate atoms and therefore IMC growth, which is mainly responsible for whisker growth in Sn coatings on brass or Cu substrates. The effects of substrate composition on whisker growth was studied by using pure Cu, brass (65 wt. % Cu 35 wt. % Zn) and Ni (bulk and electro-deposited under layer) as substrate. Whisker growth was more rapid if brass substrate was used instead of pure Cu. Whiskers were not observed when Sn was deposited on either bulk Ni or when Ni under layer was electro-deposited on brass or Cu substrates prior to Sn deposition. Ni under layer effectively stops the diffusion of Cu into Sn, thus avoiding the growth of Cu6Sn5 (which places Sn coatings under compressive stress). Thus, it is clear that continuous formation of Cu6Sn5 at the interface provides the long-term driving force for whisker growth. Since the whisker growth is a stress driven phenomenon, it is important to understand the stress evolution in Sn coatings. Stress state of the Sn coatings was studied using custom-built laser curvature set-up with multi-beam optical stress sensor (MOSS). This allowed monitoring of curvature change of the coating-substrate system in real time and the bulk average stress was calculated using Stoney’s equation. For multi-layer system such as Sn deposited on pre-deposited Ni under layer on brass substrate modified Stoney’s equation was used. In case of Sn deposited on brass without any under layer, it is known that the Cu6Sn5 IMC do not form a continuous layer at the interface between Sn and substrate under aging at ambient conditions, therefore, the curvature change due to IMC can be neglected. In addition, glancing angle X-ray diffraction was employed to analyse stress in the top surface region of the coating. The variation of glancing angle allowed probing strain at different penetration depths. Both the bulk stress and the stress in only near surface region evolve with time. The residual bulk stresses in Sn coatings are tensile immediately after deposition. The residual stresses relax very quickly upon room temperature aging and become compressive. The bulk of Sn coatings on brass substrate progressively become more compressive upon continued aging. However, stresses in Sn coatings deposited on brass substrate with Ni under layer saturate quickly at low compressive stress. Surprisingly, stress in the top-most region of Sn coating measured using XRD evolve differently. The surface of Sn coating deposited on brass substrate is compressive initially and progressively become more tensile (less compressive), while the initial compressive stress in the sample with Ni under layer saturated at a higher compressive stress than the bulk stress value recorded from curvature measurement. Therefore, the surface of the Sn coatings with Ni under layer is always more compressive than the bulk stress in the Sn coating. Therefore, a negative stress gradient for the diffusion of Sn atoms towards surface is never established and whiskers do not grow in these Sn coatings. Interestingly, through thickness voids are observed in the Sn coatings on Ni. Contrarily, in Sn coatings without Ni under layer after 170 h of aging, the surface stress becomes more tensile than the bulk of the Sn coating, favouring continuous migration of atoms from the highly compressed region near Cu6Sn5 IMC layer to the stress-free whisker root. Aforementioned observation indicates the crucial role of negative stress gradient in the mass transport of atoms required for whispering. The importance of stress and stress gradient was further studied by analysing the effect of externally imposing stress and stress gradient on whisker growth. The stresses were applied using a three-point bend setup. It has been observed that externally applied stress accelerates the whisker growth. This is mainly because applied stress alters the diffusion kinetics and growth of Cu6Sn5 IMC at the interface. However, the coating under tensile stress shows more whisker growth as compared to the coating under high compressive stress. This is attributed to the fact the coating under tensile stress is under higher negative stress gradient. Therefore, it is proposed that out-of-plane stress gradient is more important rather than the sign and the magnitude of stress in determining the propensity of whisker growth in Sn coatings.

Use of arsenic-rich groundwater for crop irrigation can increase the arsenic (As) content in food crops and act as a carcinogen, compromising human health. Using aquatic plant based phytofiltration is a potential eco-technique for removing arsenic from water. The aquatic moss species Warnstorfia fluitans grows naturally in mining areas in northern Sweden, where high concentrations of arsenic occur in lakes and rivers. This species was selected as a model for field, climate chamber and greenhouse studies on factors governing arsenic removal and arsenic phytofiltration of irrigation water. The arsenic and silicon (Si) concentrations in soil, water and plant samples were measured by AAS (atomic absorption spectrophotometry), while arsenite and arsenate species were determined using AAS combined with high pressure liquid chromatography (HPLC) with an anion exchange column. The arsenic content in grains of hybrid and local aromatic rice (Oryza sativa) cultivars with differing arsenic accumulation factor (AF) values was investigated in an arsenic hotspot in Bangladesh. The results showed that arsenic AF was important in identifying arsenic-safer rice cultivars for growing in an arsenic hotspot. The study based on silicon effect on arsenic uptake in lettuce showed that arsenic accumulation in lettuce (Lactuca sativa) could be reduced by silicon addition. The aquatic moss had good phytofiltration capacity, with fast arsenic removal of up to 82% from a medium with low arsenic concentration (1 µM). Extraction analysis showed that inorganic arsenic species were firmly bound inside moss tissue. Absorption of arsenic was relatively higher than adsorption in the moss. Regarding effects of different abiotic factors, plants were stressed at low pH (pH 2.5) and arsenic removal rate was lower from the medium, while arsenic efflux occurred in arsenate-treated medium at low (12°C) and high (30°C) temperature regimes. Besides these factors, low oxygenation increased the efficiency of arsenic removal from the medium. Finally, combining W. fluitans as a phytofilter with a lettuce crop on a constructed wetland significantly reduced the arsenic content in edible parts (leaves) of lettuce. Thus W. fluitans has great potential for use as an arsenic phytofilter in temperate regions. / <p>QC 20170323</p>

The presented thesis investigates the role of bryophytes in the deadwood and carbon (C) cycle of boreal black spruce forests in Labrador, Canada. All major forest C pools (live-tree, standing and downed deadwood, organic layer, mineral soil) were quantified for three old-growth, nine clearcut harvested, and three burned forest stands in order to characterize forest C dynamics of a high-latitude humid boreal forest ecosystem. Tree and aboveground deadwood C dynamics of Labrador black spruce forests were similar to those of drier or warmer boreal forests. However, due to bryophyte-driven processes such as woody debris (WD) burial and paludification, the studied forests contained high organic layer, mineral soil, and buried wood C stocks. The comprehensive field-measured data on C stocks was used to evaluate the CBM-CFS3, a Canadian national-scale C budget model, with respect to its applicability to Labrador black spruce and humid boreal forests elsewhere. After selected biomass estimation and deadwood decay parameters had been adjusted, the CBM-CFS3 represented measured live-tree and aboveground deadwood C dynamics well. The CBM-CFS3 was initially designed for well-drained upland forests and does not reflect processes associated with bryophytes and high forest floor moisture content, thus not capturing the large amounts of buried wood and mineral soil C observed in the studied forests. Suggestions are made for structural changes to the CBM-CFS3 and other forest ecosystem C models to more adequately represent the bryophyte-regulated accumulation of buried wood, organic layer, and mineral soil C. Accuracy of forest C models could be further improved by differentiating WD decomposition rates by disturbance history, because WD respiration reflects disturbance-induced changes in temperature and moisture regimes. In Labrador, WD respiration was limited by low WD moisture levels and high temperatures in burned stands, and by high WD moisture contents and low temperatures in old-growth stands. Following harvesting, residual vegetation prevents the desiccation of WD, resulting in significantly higher WD respiration compared to old-growth and burned stands. Moreover, the bryophyte layer recovers faster following harvest than following fire, which reduces WD desiccation due to moisture retention, water transfer, and moisture-induced cooling and results in higher WD decomposition rates. Bryophytes are thus a key driver of the deadwood and C cycle of humid boreal Labrador black spruce forests. The author recommends to classify these and similar boreal forests as a functional ecosystem group called “humid boreal forests”, preliminarily defined as “boreal forest ecosystems featuring a bryophyte-dominated ground vegetation layer associated with low soil temperatures, high moisture levels, low dead organic matter decomposition rates, and subsequently (in the absence of stand-replacing disturbances) an accumulation of buried wood embedded in a thick organic layer”. Bryophytes are also an integral component of many coniferous forests outside the boreal biome. Bryophyte-regulated processes such as WD burial or paludification are thus likely significant to the global C cycle. The potential climate change-induced release of large amounts of CO2 from buried wood and soil C pools necessitates an increased understanding of how bryophyte productivity and decomposition constraints will change with increasing temperature and varying moisture regimes. Ecosystems such as humid boreal forests with potentially high C losses to the atmosphere may thus be identified and counteractive forest management strategies can be developed and implemented. / Cette thèse de doctorat s’intéresse à l’influence qu’exercent les mousses sur les cycles du bois mort et du carbone (C) dans des pessières noires boréales humides du Labrador, Canada. Toutes les réservoirs majeurs de C (arbres vivants, bois mort sur pied et effondré, l’horizon de matière organique, sol minéral) de trois pessières vierges, neuf coupes à blanc et de trois pessières brûlées ont été quantifiés pour caractériser le cycle du C des forêts humides boréales du nord. Les dynamismes de C des arbres vivants et du bois mort supraterrestre ressemblaient à ceux des forêts boréales plus sèches ou aux températures plus chaudes. À cause des processus régulés par les mousses (l’enterrement du bois mort ou la paludification), les forêts étudiées contenaient des stocks élevés de C au sein de l’horizon de matière organique, le sol minéral et le bois enterré. Les données ont aussi été utilisées pour évaluer le MBC-SFC3, un modèle national canadien du bilan du C, concernant son applicabilité aux pessières boréales humides de Labrador et d’ailleurs. Suite à l’ajustement de quelques paramètres, p.ex. des taux de décomposition, le MBC-SFC3 reproduisait bien le dynamisme mesuré des arbres vivants et du bois mort supraterrestre. Le MBC-SFC3 a initialement été développé pour les sites bien drainés et ne considère pas les processus associés avec les mousses ou l’humidité élevée du sol. Conséquemment, le MBC-SFC3 ne représentait pas les stocks élevés de C mesurés pour le bois enterré et pour le sol. Les modifications structurelles du MBC-SFC3 et d’autres modèles du C forestier sont nécessaires pour représenter adéquatement l’accumulation du C au sein de ces réservoirs. La précision des modèles du C forestier pourrait encore être améliorée par une différenciation des taux de décomposition selon le régime de perturbations, parce que la respiration du bois mort reflète les changements de la température et d’humidité associés avec une perturbation spécifique. Dans les pessières brûlés du Labrador, la respiration du bois mort était limitée par a faible humidité du bois et des températures élevées; dans les pessières vierges, par l’humidité élevée du bois et des températures basses. Dans les coupes à blanc, la végétation résiduelle empêchait le dessèchement du bois mort. Il s’y ensuivit que la respiration du bois mort y est nettement plus élevée en comparaison avec des pessières brûlés ou vierges. La décomposition du bois mort après coupe à blanc est aussi favorisée par la récupération plus rapide de la couche de mousses, diminuant conséquemment le dessèchement du bois mort par la conservation d’humidité, les transports vertical et horizontale d’eau et le refroidissement induit par l’humidité. Ainsi, les mousses sont les facteurs clés dans les cycles du bois mort et du C des pessières noires boréales au Labrador. L’auteur préconise la classification de ces pessières et des forêts semblables comme un groupe fonctionnel d’écosystèmes nommé : « pessières boréales humides » ; provisoirement définies comme « des écosystèmes forestiers avec une végétation terrestre dominée par les mousses et par conséquent associée avec des températures basses du sol, une humidité élevée, des taux de décomposition faibles et (en l’absence de perturbations) l’accumulation du bois enterré dans des couches organiques epaisses ». En outre, les mousses sont des éléments principaux des nombreuses forêts résineuses n’appartenant pas au biome boréal. Les processus régulés par les mousses tels l’enterrement du bois mort ou la paludification sont probablement importants pour le cycle global de C. La libération potentielle de grandes quantités de CO2 des réservoirs « bois enterré » et « sol » à la suite des changements climatiques exige une meilleure compréhension des transformations de la productivité des mousses et des limitations de la décomposition dues aux températures plus élevées et au taux d’humidités variables. Ainsi, les écosystèmes aux pertes potentielles de C élevées (p.ex. les pessières boréales humides) peuvent être identifiés et des mesures d’aménagement antagonistes peuvent être développées et implémentées. Traduction assistée par : Karl-Heinrich von Bothmer, Géry van der Kelen / Die vorliegende Arbeit untersucht die Einflüsse von Moosen auf den Totholz- und Kohlenstoff-(C)-Kreislauf in borealen Schwarzfichtenwäldern in Labrador, Kanada. Um den C-Kreislauf dieses humiden borealen Waldökosystems zu charakterisieren, wurden alle bedeutenden C-Speicher (lebende Bäume, stehendes und liegendes Totholz, organische Auflage, Mineralboden) von drei Primärwald-, neun Kahlschlags- und drei Brandflächen quantifiziert. Die C-Dynamiken der Bäume und des oberiridischen Totholzes der Untersuchungsflächen ähnelten denen von trockeneren und/oder wärmeren borealen Wäldern, während die organische Auflage, der Mineralboden und das begrabene Totholz bedingt durch von Moosen regulierte Prozesse wie Totholzeinlagerung und Paludifizierung besonders hohe C-Vorräte aufwiesen. Mit dem umfangreichen C-Datensatz wurde das CBM-CFS3, das nationale kanadische C-Modell, am Beispiel Labradors im Hinblick auf seine Anwendbarkeit in humiden borealen Wäldern evaluiert. Nach Anpassung ausgewählter Parameter, z.B. der Totholzabbauraten, wurden die gemessenen C-Dynamiken der Bäume und des oberiridischen Totholzes vom Modell abgebildet. Das CBM-CFS3 wurde ursprünglich für staunässefreie, terrestrische Waldstandorte entwickelt und berücksichtigt keine mit Moosen oder hoher Bodenfeuchte assoziierten Prozesse, so dass es die hohen C-Vorräte des begrabenen Totholzes und des Bodens nicht widerspiegelte. Eine adäquate Abbildung der Akkumulation von C in diesen Speichern erfordert strukturelle Änderungen des CBM-CFS3 und anderer Wald-C-Modelle. Die Genauigkeit von Wald-C-Modellen könnte darüber hinaus durch eine Differenzierung der Totholzabbauraten in Abhängigkeit vom Störungsregime verbessert werden, da störungsspezifische Veränderungen von Temperatur und Feuchte von der Totholzatmung widergespiegelt werden. Im Untersuchungsgebiet limitierten geringe Holzfeuchten und hohe Holztemperaturen die Totholzatmung auf Brandflächen. In Primärwäldern wirkten dagegen hohe Holzfeuchten und geringe Holztemperaturen hemmend. Auf Kahlschlägen verhinderte die verbleibende Vegetation die Austrockung des Totholzes, was zu signifikant erhöhten Atmungsraten im Vergleich zu Brand- und Primärwaldflächen führte. Zudem wird der Totholzabbau auf Kahlschlen durch eine schnellere Erholung der Moosdecke als auf Brandflächen gefördert, da Moose durch ihr hohes Wasserspeichervermögen, vertikalen und horizontalen Wassertransport und feuchte-induzierte Kühlung der Austrockung des Totholzes entgegenwirken. Moose sind somit ein Schlüsselfaktor im Totholz- und C-Kreislauf der humiden borealen Schwarzfichtenwälder Labradors. Die Autorin empfiehlt die Klassifikation dieser und ähnlicher borealer Wälder als eine funktionelle Ökosystemgruppe namens “humid boreal forests”; vorläufig definiert als “boreale Waldökosysteme mit durch Moose dominierter Bodenvegetation und damit assoziierten niedrigen Bodentemperaturen, hohen Bodenfeuchten, geringen Abbauraten und (in Abwesenheit großflächiger Störungen) der Akkumulation von begrabenem Totholz in mächtigen organischen Auflagen”. Auch außerhalb des borealen Bioms sind Moose ein wesentlicher Bestandteil vieler Nadelwälder. Durch Moose regulierte Prozesse wie Totholzeinlagerung und Paludifizierung sind daher wahrscheinlich relevant für den globalen C-Kreislauf. Die durch den Klimawandel bedingte potentielle Freisetzung von großen Mengen CO2 aus begrabenem Totholz und dem Boden macht ein besseres Verständnis der zu erwartenden Veränderungen von Mooswachstum und Abbauhemmnissen als Folge erhöhter Temperaturen und variabler Feuchteverhältnisse erforderlich. Somit können Ökosysteme mit potentiell hohen C-Verlusten, wie z.B. humide boreale Wälder, identifiziert und diesen entgegenwirkende Bewirtschaftungsmaßnahmen entwickelt und umgesetzt werden.

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Einige wenig bekannte Aspekte der Biologie der Peloridiidae (Verhalten, intraspezifische Kommunikation, Wirtspflanzenassoziationen, Feinmorphologie usw.) wurden untersucht. Die gewonnenen Informationen wurden benutzt, um eine phylogenetische Hypothese zu Verhältnissen der Peloridiidae untereinander und zu anderen Hemiptera aufzustellen. Wirtspflanzen der Peloridiidae wurden in Australien, Chile und Neuseeland systematisch besammelt. Peloridiidae als Familie scheinen keine Präferenz für ein Taxon der Bryophyta zu haben, auch wenn sie eine Affinität zu einigen Gruppen der Moose zeigen. Unterschiedliche Arten und Gattungen der Peloridiidae können sich aber in ihrer Selektivität unterscheiden. Vibrationssignale von vier Arten der Peloridiidae wurden zum ersten Mal untersucht. Einige Eigenschaften dieser Signale variierten zwischen den Arten: australische und südamerikanische Vertreter waren einander ähnlich, die neuseeländischen unterschieden sich aber von ihnen beiden. Detaillierte Informationen zu feinen morphologischen Merkmalen der Antennen, Labiumspitze, Tarsen, Integumentaldrüsen usw. in 21 Arten der Peloridiidae und einigen Außengruppen wurden zum ersten Mal präsentiert. Die erarbeiteten Merkmale wurden zur Herstellung einer phylogenetischen Hypothese herangezogen. Die Peloridiidae erwiesen sich da als ein Monophylum, dessen Schwestergruppe die Auchenorrhyncha waren. Dieses Verhältnis wird anhand von Daten aus Literatur und anderen Untersuchungen diskutiert und etwas in Frage gestellt. Die intrafamiliären Verhältnisse der Peloridiidae sind nach der erarbeiteten phylogenetischen Hypothese denen aus Literatur bekannten ähnlich; der wichtige Unterschied ist die basale Position der Gattung Peloridium. In einer Analyse mit zusätzlichen drei verhaltensökologischen Merkmalen ändert Peloridium aber seine Position, was das Potential der integrativen Ansätze illustriert, aber vorsichtig interpretiert werden muss, da solche Merkmale schwer zu homologisieren sind. / Some insufficiently studied aspects of Peloridiidae biology such as behavior, intraspecific communication, host plant preferences and fine morphology were investigated. The newly acquired information was used for production of a phylogenetic hypothesis on Peloridiidae relationships and critical evaluation of the existing ones. Host plants of Peloridiidae were studied systematically in Australia, Chile and New Zealand. Peloridiidae as a whole were found not to be bound to particular bryophyte taxa, although they regularly occurred in species of Dicranaceae, Hypopterygiaceae, Polytrichaceae and Sphagnaceae. Still, different species and genera could vary in their host plant specificity. Vibrational signals of four Peloridiidae species were studied for the first time. Features of these signals varied between species, the Australian and South American ones being similar to each other and the New Zealand species different from both of them. Detailed information on fine morphology of antennae, genae, labium tip, tegminal sculpture, tarsi, abdominal sculpture and integumental glands in 21 Peloridiidae species and some sister groups was presented for the first time. The findings were formalized as a matrix of 93 characters and analyzed phylogenetically with methods of maximum parsimony. A monophyletic Peloridiidae resulted, with significant support of the sister-group relationship to Auchenorrhyncha. This relationship was discussed on the background of other studies and literature data. The intrafamiliar structure of Peloridiidae in the present study was quite similar to previously published works, with the major exception of the genus Peloridium branching off most basally in the phylogenetic tree. Three additional bioacoustic and behavioral characters, when integrated into the matrix, change the position of Peloridium and demonstrate the potential of integrative approaches, although this result must be treated with care due to complicated homologization of behavioral traits. / В данной работе исследуется ряд недостаточно изученных ранее аспектов биологии семейства Peloridiidae: поведение, внутривидовая коммуникация, трофические связи с растениями и тонкие детали морфологии. Полученная информация используется для создания новой филогенетической гипотезы о родственных связях Peloridiidae и для критической оценки существующих гипотез. Кормовые растения семейства систематически изучены в Австралии, Новой Зеландии и Чили. Peloridiidae в целом, как выяснилось, не привязаны к отдельным таксонам мохообразных, хотя они регулярно встречались на представителях Dicranaceae, Hypopterygiaceae, Polytrichaceae и Sphagnaceae. Однако, трофическая специфичность отдельных родов и видов может сильно различаться. Впервые изучены вибрационные сигналы четырех видов пелоридиид. Черты сигналов различались внутри семейства: сигналы южноамериканских и австралийских видов были похожи, в то время как новозеландские виды от них отличались. Впервые представлена подробная информация о морфологии антенн, кончика хоботка, лапок, скульптуры тегменов, брюшка и покровных желез для 21 вида пелоридиид и некоторых внешних групп. Эти находки были организованы в матрицу из 93 признаков и проанализированы филогенетически с помощью методов минимизации изменений. В результате монофилетические Peloridiidae оказались сестринской группой монофилетических Auchenorrhyncha, с неплохим статистическим подтверждением. Эта группировка обсуждается в свете других работ и данных литературы. Внутренняя структура семейства в настоящей работе оказалась довольно похожей на данные литературы, за важным исключением рода Peloridium, который оказался на самом нижнем ответвлении филогенетического древа. Когда к анализу были привлечены три дополнительных признака (биоакустические и поведенческие), позиция Peloridium изменилась. Этот результат иллюстрирует потенциал интегративных методов, хотя и требует осторожного к себе отношения из-за сложностей гомологизации поведенческих признаков.

Dans la forêt boréale, l’augmentation de la fréquence et de la superficie d’îlots de pessières à lichens sur le territoire québécois a déjà été observée et pourrait résulter en une migration vers le sud de la limite nordique des pessières à mousses. Ce phénomène survient après des échecs de régénération, qui ont lieu lorsque le milieu est préalablement fragilisé lorsqu’une nouvelle perturbation affecte le peuplement. Avec la possibilité de détecter ce stress en analysant les propriétés spectrales de la végétation, les zones perturbées pourraient alors être identifiées. L’objectif principal de la présente étude est d’établir des liens entre d’une part, les informations extraites des signatures spectrales et d’autre part, les indices de végétation et les différents types de stress affectant les écosystèmes boréaux. Cela permettra de savoir s’il est possible d’identifier les pessières à mousses à risque de subir un accident de régénération en étudiant les propriétés spectrales de la végétation comme indicateur de stress. Pour répondre à cet objectif, des sites d’échantillonnage ont été positionnées aux 51e, 52e et 53e parallèles le long de la route de la baie James. Les placettes ont été regroupées en paires afin de faire des tests appariés et ainsi comparer les deux types de peuplements. Sur le terrain, les signatures spectrales ont été prises sur les feuilles aléatoirement prélevées sur cinq épinettes noires. Ces mesures ont été prises tout au long de la saison de croissance (3 campagnes d’échantillonnage). Quatre indices de végétation (NDVI, NDWI, PRI et SIPI) ont été extraits des signatures spectrales, et la pente moyenne du red-edge a été calculée. Les résultats obtenus ont permis de déterminer que certaines des pessières à mousses ont des valeurs très proches de celles des pessières à lichens, qui sont considérées comme des écosystèmes stressés. À partir de ces résultats, il est possible de supposer que le stress peut également être identifié à l’échelle du paysage (sur les images satellitaires) et ainsi permettre un suivi et une gestion après les feux et les épidémies afin de limiter les pertes de ce précieux écosystème. / In the boreal forest of northern Québec, the size and quantity of lichen woodlands patches is increasing, and taking over the spruce-moss forest territory. The phenomenon has been observed, and scientists now believe that the northern limit of the spruce-moss forest will slowly move south. This shift of ecosystem happens when the forest stand is already fragilized, and a perturbation occurs. Vegetation’s spectral properties can be used as a tool to assess and identify disturbed forest areas The main objective of this study is to establish relations between data extracted from spectral signatures, vegetation indexes and different types of stress that could affect boreal ecosystems. The identification spruce-moss woodlands prone to regeneration failure could be achieved with the study of spectral properties as stress indicators. In order to achieve this objective, sites from 3 latitudes (51, 52 and 53) have been sampled on James Bay Road. Plots have been regrouped in pairs for subsequent pairwise statistical tests to compare results from both forest stand types. Spectral signatures have been measured on 5 randomly chosen black spruces. These measurements were taken throughout the growing season (3 sampling campaigns). Four vegetation indexes have been extracted from spectral signatures (NDVI, NDWI, PRI and SIPI), and the mean slope of the red-edge area have been calculated. Results have shown that some of the spruce-moss stands have had very similar values to those from the lichen woodlands, that are considered as stressed ecosystems. From these results, it is possible to assume that stressed ecosystems can be detected at landscape level (on satellite images). Monitoring vegetation stress can help improve forest management after forest fires and insect’s epidemics to prevent the loss of this beautiful ecosystem.

Northern Canadian peatlands contain vast deposits of carbon. It is with growing urgency that we seek a better understanding of their assimilative capacity. Assimilative capacity and peat accumulation in raised bogs are linked to primary productivity of resident Sphagnum species. Understanding moisture-mediated photosynthesis of Sphagnum spp. is central to understanding peat production rates. The relationship between depth to water table fluctuation and spectral reflectance of Sphagnum moss was investigated using multispectral imaging at a recovering raised bog on the southwest coast of British Columbia, Canada. Burns Bog is a temperate oceanic ombrotrophic bog. Three ecohydrological indicator species of moss were chosen for monitoring: S. capillifolium, S. papillosum, and S. cuspidatum. Three spectral vegetation indices (SVIs) were used to characterize Sphagnum productivity: the normalized difference vegetation index 660, the chlorophyll index, and the photochemical reflectance index. In terms of spectral sensitivity and the appropriateness of SVIs to species and field setting, we found better performance for the normalized difference vegetation index 660 in the discrimination of moisture mediated species-specific reflectance signals. The role that spatiotemporal scale and spectral mixing can have on reflectance signal fidelity was tested. We were specifically interested in the relationship between changes in the local water table and Sphagnum reflectance response, and whether shifting between close spatial scales can affect the statistical strength of this relationship. We found a loss of statistical significance when shifting from the species-specific cm2 scale to the spectrally mixed dm2 scale. This spatiospectral uncoupling of the moisture mediated reflectance signal has implications for the accuracy and reliability of upscaling from plot based measurements. In terms of species-specific moisture mediated reflectance signals, we were able to effectively discriminate between the three indicator species of Sphagnum along the hummock-to-hollow gradient. We were also able to confirm Sphagnum productivity and growth outside of the vascular growing season, establishing clear patterns of reflectance correlated with changes in the local moisture regime. The strongest relationships for moisture mediated Sphagnum productivity were found in the hummock forming species S. capillifolium. Each indicator Sphagnum spp. of peat has distinct functional traits adapted to its preferred position along the ecohydrological gradient. We also discovered moisture mediated and species-specific reflectance phenologies. These phenospectral characteristics of Sphagnum can inform future monitoring work, including the creation of a regionally specific phenospectral library. It’s recommended that further close scale multispectral monitoring be carried out incorporating more species of moss, as well as invasive and upland species of concern. Pervasive vascular reflectance bias in remote sensing products has implications for the reliability of peatland modelling. Avoiding vascular bias, targeted spectral monitoring of Sphagnum indicator species provides a more reliable measure for the modelling of peatland productivity and carbon assimilation estimates. / Graduate