Thesis (M.N.R.M.)--University of Manitoba, 2001. / Includes bibliographical references (leaves 119-138).

Large amounts of carbon (C) are stored in tundra soils. Global warming may turn tundra ecosystems from C sinks into sources or vice versa, depending on the balance between gross primary production (GPP), ecosystem respiration (ER) and the resulting net ecosystem exchange (NEE). We aimed to quantify the summer season C balance of a 27 km2 tundra landscape in subarctic Sweden. We measured CO2 fluxes in 37 widely distributed plots across five tundra vegetation types and in 7 additional bare soil plots, to assess effects of abiotic and biotic components on C exchange. C fluxes in bare soils were low and differed to all vegetation types. Thus, accounting for differences between bare soils and vegetated parts is crucial for upscaling a C balance using a landcover classification map. In addition, we found that both NEE and ER, varied within and across different tundra vegetation types. The C balance model for the growing season 2016 revealed a net C loss to the atmosphere. Most vegetation types acted as CO2 sources, with highest source strength in dense shrub vegetation at low elevations. The only considerable C sinks were graminoid-dominated upland meadows. In addition, we found a shift in C balance between different heath vegetation types, ranging from C source in dense deciduous shrub vegetation (Mesic Heath and Dry Heath) to C sink in low growing shrub vegetation (Extremely Dry Heath). These results highlight the importance to account for differences between vegetation types when modelling C fluxes from plot to landscape level.

An inclined point frame was used to measure leaf area indicies in an alpine tundra Kobresia stand and Deschampsia meadow on Niwot Ridge, Colorado. Measurements were made throughout the summer of 1971 at vi various heights in the canopy and for each species in the two communities. Maximum leaf area indices of 2.2 and 2.0 occurred in the Kobresia and Deschampsia sites, respectively. The Kobresia site was characterized by a single dominant species, Kobresia myosuroides, and a predominance of vegetation within 2.5 cm of mean ground level. The Deschampsia site had no single dominant species. The region of maximum foliage shifted from the 2.5 to 5 cm height zone in June to the 5 to 10 cm zone in early August. Phenological observations revealed a greater number of vegetative contacts in the Deschampsia site on all sampling dates. Certain shared species varied in their phenological patterns. It is suggested that differences in the duration of snow cover and surface melt-water may be related to the variation in phenological patterns in the two sites. In both communities, maximum LAI occurred when flower and fruit production overlapped. Arctic tundra LAI values, measured using similar methods, were less than half the maximum LAI values reached in the alpine communities examined here.

<p> Evaporation was calculated for a subarctic beach ridge, near Churchill, Manitoba, using the energy balance approach. Energy balance calculations for the measurement season revealed an average Bowen ratio, β, of 0.68, with a value of 1.00 representing α' (the evaporability parameter). Fifty-seven percent of the net radiation was utilized by the evaporative heat flux over this tundra surface. Regressions were used to determine the most likely combination of environmental variables responsible for the behaviour of evaporation. Surface soil moisture remained relatively constant throughout the summer measurement period and soil temperatures appeared to be unrelated to evaporation. Air temperature proved to be insignificant to the evaporation flux, and net radiation alone could only account for 54% of the variability. The combination of the net radiation and the wet and dry bulb temperature depression at 1 m accounted for 88% of the variability of the evaoorative heat flux. The mean α' for a site is assumed to be controlled by the surface type in simplified variations of the combination model. The conclusion has been drawn from this study that the variability of α' can be accounted for by variable atmospheric humidities as well as net radiation. The importance of this atmospheric control on the rate of evaporation is emphasized.</p> / Thesis / Master of Science (MSc)

Migratory animals face numerous challenges that are often exacerbated by climate change. In the Arctic, where climate change is occurring at 4x the average global rate, species must adapt rapidly to novel conditions. I studied four species of sea ducks (Long-tailed Ducks Clangula hyemalis and Steller’s Polysticta stelleri, Spectacled Somateria fischeri, and King Eiders S. spectabilis), of which Steller’s and Spectacled Eiders are federally Threatened, and all are well below historic population sizes. I conducted three studies to assess how female sea ducks interact with their habitats between arrival on the breeding grounds and nesting. First, I assessed patterns of occurrence within diverse tundra wetland types by female sea ducks, in relation to three metrics of wetland resource availability: wetland surface area and biomass in benthic cores and emergent sweeps separately. I also monitored activity budgets of female sea ducks. Wetlands containing the emergent grass Arctophila fulva were highly selected for by all species relative to the wetland surface area and biomasses of prey, while large lakes, streams, and wetlands lacking Arctophila were avoided. Most time was allocated towards foraging or loafing, emphasizing the importance of energy acquisition during this transitional time period following migration and prior to nesting. Wetlands selected for broadly across species are under threat as climate change reduces the prevalence of these wetland types on the landscape, requiring adaptation to such novel conditions. My second study assessed how sea ducks rely upon prey resources within tundra wetlands, and upon stored tissues acquired in marine habitats. Female sea ducks must both produce eggs and sustain themselves throughout a ~30-day period from egg-laying through hatch, with potentially different nutrient sources for each aspect of the reproductive process. I sampled stable isotopes of proteins in egg membranes (reproductive endpoint) and in red blood cells (body maintenance endpoint), which I modeled relative to stable isotopes in a suite of prey taxa from freshwater tundra ponds and marine habitats. Across all four species, most proteins came from tundra wetlands (≥ 89% of modeled protein sources) for egg production. Smaller-bodied long-tailed Ducks and Steller’s Eiders relied heavily on the local environment for body maintenance and survival (red blood cells) during incubation, but larger Spectacled and King Eiders only gained ~60% of proteins locally, relying on the remaining 40% from body tissues acquired previously from marine habitats. Local wetlands provided 60-99% of proteins for female sea ducks. Freshwater habitats in which sea ducks forage warrant protection, and conservation for some species requires interagency cooperation across tundra, freshwater wetlands, and marine habitats. My third study assessed patterns of nest site selection across species, years, and spatial scales. How females choose nest sites has major implications for population processes. Decisions integrate information across spatial scales for each component of habitat a hen considers. I used boosted regression trees (a machine learning technique) to model suitability of nesting habitat for 414 variables of habitat features at six spatial scales. Social association with other ducks were highly important in determining suitability. Suitable habitat varied spatiotemporally among species, but the relative amount of suitable habitat was consistent across years for each species. Conservation for suitable habitat must include broad areas to incorporate interannual variability. Through these three studies, I assessed the relative use of; importance of; and reliance upon various wetland types, the relative importance of marine versus freshwater nutrients for reproduction, and the factors driving nest site selection in a guild of sea ducks facing imminent climate change.

The relationship between soil temperature and CO₂ flux from undisturbed soil cores was examined during freeze-up of arctic tundra. Three habitats which dominate tundra topography, polygon trough, ridge and basin, produced significantly different amounts of CO₂ when soil temperatures were above 0 C. A significant positive correlation between soil temperatures between 10 to -7 C and CO₂ flux from each habitat was established. Substantial quantities of CO₂ were produced during freeze-up period when soil temperatures remained near 0 C for an extended period, and the CO₂ production continued at reduced levels as the soil temperature dropped below 0 C. When soil temperatures reached -7 C and the study was terminated, the CO₂ flux was reduced to a low level, but did not reach extinction. A maximum CO₂ flux of 2925 mg CO₂/m²/day from the trough habitat was observed when the soil temperature was 10 C, and the minimum CO₂ flux of 131 mg/m²/day was observed when the soil temperature was -7 C. These data are consistant with the hypothesis that soil microorganisms in arctic tundra are capable of physiological activity in the range of 0 to -7 C. / Master of Science

Global climate models predict that the current trend of warming in the Arctic will continue over the next century. The productivity of arctic plants is often limited by short growing seasons with relatively low temperatures such that a warmer climate could have large impacts on plants and plant communities. This study characterised alpine plant responses to changes in temperature at an alpine tundra site near Whitehorse, Yukon, Canada. I examined relationships between plant productivity and natural temperature variations and assessed responses of plants exposed to an experimental warming treatment. Non-destructive measurements of reproductive and growth characteristics of four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum, and Salix arctica) were taken annually from 1999 to 2008. There was no significant effect of the warming treatment (OTCs) on average daily mean temperatures as midday warming of up to 1.4 °C was largely offset by night time cooling in the OTCs. Vegetative measurements of target species showed no significant responses to OTC treatments. However, peduncles of D. octopetala and sections of P. viviparum inflorescences that produced bulbils were an average of 34.6 % and 64.7 % longer in OTCs than in controls, respectively. These treatment responses were likely due to plants responding to a factor other than temperature that was modified by the chamber. One vegetative and five reproductive characteristics were significantly related to annual variation in temperature. The summer of 2004 was exceptionally hot, and some species that did not respond to smaller fluctuations in temperature showed large changes in growth or reproduction in this year, perhaps indicating a non-linear response to temperature. Among the larger responses to the warm summer of 2004 was a shift in P. viviparum allocation from predominantly asexual to sexual means of reproduction. Measurements of plant community composition assessed at five-year intervals showed no differences in community composition between experimental plots and controls, and changes in composition over the study period were not uni-directional. In general, both individual plants and community composition were highly resilient to observed variation in summer temperatures. Other factors, such as nutrient availability, may be more important in determining plant responses to environmental change at this site than the direct effects of summer temperature variation.

Global climate models predict that the current trend of warming in the Arctic will continue over the next century. The productivity of arctic plants is often limited by short growing seasons with relatively low temperatures such that a warmer climate could have large impacts on plants and plant communities. This study characterised alpine plant responses to changes in temperature at an alpine tundra site near Whitehorse, Yukon, Canada. I examined relationships between plant productivity and natural temperature variations and assessed responses of plants exposed to an experimental warming treatment. Non-destructive measurements of reproductive and growth characteristics of four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum, and Salix arctica) were taken annually from 1999 to 2008. There was no significant effect of the warming treatment (OTCs) on average daily mean temperatures as midday warming of up to 1.4 °C was largely offset by night time cooling in the OTCs. Vegetative measurements of target species showed no significant responses to OTC treatments. However, peduncles of D. octopetala and sections of P. viviparum inflorescences that produced bulbils were an average of 34.6 % and 64.7 % longer in OTCs than in controls, respectively. These treatment responses were likely due to plants responding to a factor other than temperature that was modified by the chamber. One vegetative and five reproductive characteristics were significantly related to annual variation in temperature. The summer of 2004 was exceptionally hot, and some species that did not respond to smaller fluctuations in temperature showed large changes in growth or reproduction in this year, perhaps indicating a non-linear response to temperature. Among the larger responses to the warm summer of 2004 was a shift in P. viviparum allocation from predominantly asexual to sexual means of reproduction. Measurements of plant community composition assessed at five-year intervals showed no differences in community composition between experimental plots and controls, and changes in composition over the study period were not uni-directional. In general, both individual plants and community composition were highly resilient to observed variation in summer temperatures. Other factors, such as nutrient availability, may be more important in determining plant responses to environmental change at this site than the direct effects of summer temperature variation.

The Arctic tundra, covering approx. 5.5 % of the Earth’s land surface, is one of the last ecosystems remaining closest to its untouched condition. Remote sensing is able to provide information at regular time intervals and large spatial scales on the structure and function of Arctic ecosystems. But almost all natural surfaces reveal individual anisotropic reflectance behaviors, which can be described by the bidirectional reflectance distribution function (BRDF). This effect can cause significant changes in the measured surface reflectance depending on solar illumination and sensor viewing geometries. The aim of this thesis is the hyperspectral and spectro-directional reflectance characterization of important Arctic tundra vegetation communities at representative Siberian and Alaskan tundra sites as basis for the extraction of vegetation parameters, and the normalization of BRDF effects in off-nadir and multi-temporal remote sensing data. Moreover, in preparation for the upcoming German EnMAP (Environmental Mapping and Analysis Program) satellite mission, the understanding of BRDF effects in Arctic tundra is essential for the retrieval of high quality, consistent and therefore comparable datasets. The research in this doctoral thesis is based on field spectroscopic and field spectro-goniometric investigations of representative Siberian and Alaskan measurement grids. The first objective of this thesis was the development of a lightweight, transportable, and easily managed field spectro-goniometer system which nevertheless provides reliable spectro-directional data. I developed the Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS). The outcome of the field spectro-radiometrical measurements at the Low Arctic study sites along important environmental gradients (regional climate, soil pH, toposequence, and soil moisture) show that the different plant communities can be distinguished by their nadir-view reflectance spectra. The results especially reveal separation possibilities between the different tundra vegetation communities in the visible (VIS) blue and red wavelength regions. Additionally, the near-infrared (NIR) shoulder and NIR reflectance plateau, despite their relatively low values due to the low structure of tundra vegetation, are still valuable information sources and can separate communities according to their biomass and vegetation structure. In general, all different tundra plant communities show: (i) low maximum NIR reflectance; (ii) a weakly or nonexistent visible green reflectance peak in the VIS spectrum; (iii) a narrow “red-edge” region between the red and NIR wavelength regions; and (iv) no distinct NIR reflectance plateau. These common nadir-view reflectance characteristics are essential for the understanding of the variability of BRDF effects in Arctic tundra. None of the analyzed tundra communities showed an even closely isotropic reflectance behavior. In general, tundra vegetation communities: (i) usually show the highest BRDF effects in the solar principal plane; (ii) usually show the reflectance maximum in the backward viewing directions, and the reflectance minimum in the nadir to forward viewing directions; (iii) usually have a higher degree of reflectance anisotropy in the VIS wavelength region than in the NIR wavelength region; and (iv) show a more bowl-shaped reflectance distribution in longer wavelength bands (>700 nm). The results of the analysis of the influence of high sun zenith angles on the reflectance anisotropy show that with increasing sun zenith angles, the reflectance anisotropy changes to azimuthally symmetrical, bowl-shaped reflectance distributions with the lowest reflectance values in the nadir view position. The spectro-directional analyses also show that remote sensing products such as the NDVI or relative absorption depth products are strongly influenced by BRDF effects, and that the anisotropic characteristics of the remote sensing products can significantly differ from the observed BRDF effects in the original reflectance data. But the results further show that the NDVI can minimize view angle effects relative to the contrary spectro-directional effects in the red and NIR bands. For the researched tundra plant communities, the overall difference of the off-nadir NDVI values compared to the nadir value increases with increasing sensor viewing angles, but on average never exceeds 10 %. In conclusion, this study shows that changes in the illumination-target-viewing geometry directly lead to an altering of the reflectance spectra of Arctic tundra communities according to their object-specific BRDFs. Since the different tundra communities show only small, but nonetheless significant differences in the surface reflectance, it is important to include spectro-directional reflectance characteristics in the algorithm development for remote sensing products. / Die arktische Tundra ist mit circa 5,5 % der Landoberfläche eines der letzten großen verbliebenen fast unberührten Ökosysteme unserer Erde. Nur die Fernerkundung ist in der Lage, benötigte Informationen über Struktur und Zustand dieses Ökosystems großräumig und in regelmäßigen Zeitabständen zur Verfügung zu stellen. Aber fast alle natürlichen Oberflächen zeigen individuelle anisotrope Reflexionsverhaltensweisen, welche durch die bidirektionale Reflektanzverteilungsfunktion (englisch: BRDF) beschrieben werden können. Dieser Effekt kann zu erheblichen Veränderungen im gemessenen Reflexionsgrad der Oberfläche in Abhängigkeit von den solaren Beleuchtung- und Blickrichtungsgeometrien führen. Zielstellung dieser Arbeit ist die hyperspektrale und spektro-direktionale Charakterisierung der Oberflächenreflexion wichtiger und repräsentativer arktischer Pflanzengesellschaften in Sibirien und Alaska, als Grundlage für die Extraktion von Vegetationsparametern und die Normalisierung von BRDF-Effekten in Off-Nadir und multi-temporalen Fernerkundungsdaten. In Vorbereitung auf die bevorstehende nationale EnMAP Satellitenmission ist ein Grundverständnis der BRDF-Effekte in der arktischen Tundra von wesentlicher Bedeutung für die Erstellung von hochqualitativen, konsistenten und damit vergleichbaren Datensätzen. Die in dieser Arbeit genutzten Daten beruhen auf geländespektroskopische und geländespektro-goniometrische Untersuchungen von repräsentativen Messflächen in Sibirien und Alaska. Die Entwicklung eines leichten, transportablen und einfach anzuwendenden Geländespektro-Goniometers, welches dennoch zuverlässig Daten liefert, war die erste Aufgabe. Hierfür habe ich ein Gerät mit der Bezeichnung ManTIS („Manual Transportable Instrument platform for ground-based Spectro-directional observations“) entwickelt. Die Ergebnisse der geländespektro-radiometrischen Messungen entlang wichtiger ökologischer Gradienten (regionales Klima, pH-Wert des Bodens, Bodenfeuchte, Toposequenz) zeigen, dass die Pflanzengesellschaften sich anhand ihrer Nadir-Reflektanzen unterscheiden lassen. Insbesondere die Möglichkeit der Differenzierung im sichtbaren (VIS) blauen und roten Wellenlängenbereich. Die Nah-Infrarot (NIR) Schulter und das NIR-Reflektanzplateau sind trotz ihrer niedrigeren Reflektanzwerte eine wertvolle Informationsquelle, die genutzt werden kann um die Pflanzengesellschaften entsprechend ihrer Biomasse und der Vegetationsstruktur voneinander zu unterscheiden. Im Allgemeinen zeigen die verschiedenen Pflanzengesellschaften der Tundra: (i) eine niedrige maximale NIR-Reflektanz; (ii) ein schwaches oder nicht sichtbares lokales Reflektanzmaximum im grünen VIS-Spektrum; (iii) einen schmalen „red-edge“ Bereich zwischen dem roten und NIR-Wellenlängenbereich und (iv) kein deutliches NIR-Reflektanzplateau. Diese gemeinsamen Nadir-Reflektanzeigenschaften sind entscheidend für das Verständnis der Variabilität der BRDF-Effekte in der arktischen Tundra. Keine der untersuchten Pflanzengesellschaften wies isotrope Reflektanzeigenschaften auf. Im Allgemeinen zeigt Tundravegetation: (i) die höchsten BRDF-Effekte in der solaren Hauptebene; (ii) die maximalen Reflexionsgrade in den rückwärts gerichteten Blickrichtungen; (iii) höhere Grade an Anisotropie im VIS-Spektrum als im NIR-Spektrum und (iv) schüsselförmige Reflexionsgradverteilungen in den längeren Wellenlängenbereichen (>700 nm). Die Analyse des Einflusses von hohen Sonnenzenitwinkeln auf die Anisotropie der Rückstrahlung zeigt, dass sich mit zunehmenden Sonnenzenitwinkeln die Anisotropie-Eigenschaften in azimutal-symmetrische schüsselförmige Reflexionsgradverteilungen ändern. Auch ergeben die spektro-direktionalen Analysen, dass Fernerkundungsprodukte wie der NDVI oder die relative Absorptionstiefe stark von BRDF-Effekten beeinflusst werden. Die anisotropen Eigenschaften der Fernerkundungsprodukte können sich erheblich von den beobachteten BRDF-Effekten in den ursprünglichen Reflektanzdaten unterscheiden. Auch lässt sich aus den Ergebnissen ableiten, dass der NDVI relativ gesehen die blickrichtungsabhängigen BRDF-Effekte minimieren kann. Für die untersuchten Pflanzengesellschaften der Tundra weichen die Off-Nadir NDVI-Werte nie mehr als 10 % von den Nadir-NDVI-Werten ab. Im Resümee dieser Studie wird nachgewiesen, dass Änderungen in der Sonnen-Objekt-Sensor-Geometrie direkt zu Reflektanzveränderungen in den Fernerkundungsdaten von arktischen Pflanzengesellschaften der Tundra entsprechend ihrer objekt-spezifischen BRDF-Charakteristiken führen. Da die verschiedenen Arten der Tundravegetation nur kleine, aber signifikante Unterschiede in der Oberflächenreflektanz zeigen, ist es wichtig die spektro-direktionalen Reflexionseigenschaften bei der Entwicklung von Algorithmen für Fernerkundungsprodukte zu berücksichtigen.

In recent years, concern has grown over the consequences of global warming. The arctic region is thought to be particularly vulnerable to increasing temperatures, and warming is occurring here substantially more rapidly than at lower latitudes. Consequently, assessments of the state of the Arctic are a focus of international efforts. For the terrestrial Arctic, large datasets are generated by remote sensing of above-ground variables, with an emphasis on vegetation properties, and, by association, carbon fluxes. However, the terrestrial component of the carbon (C) cycle remains poorly quantified and the below-ground distribution and stocks of soil C can not be quantified directly by remote sensing. Large areas of the Arctic are also difficult to access, limiting field surveys. The scientific community does know, however, that this region stores a massive proportion (although poorly quantified, soil C stocks for tundra soils vary from 96 to 192 Gt C) of the global reservoir of soil carbon, much of it in permafrost (900 Gt C), and these stocks may be very vulnerable to increased rates of decomposition due to rising temperatures. The consequences of this could be increasing source strength of the radiatively forcing gases carbon dioxide (CO2) and methane (CH4). The principal objective of this project is to provide a critical evaluation of methods used to link soil C stocks and fluxes at the usual scales spanned by the field surveys (centimetre to kilometre) and remote sensing surveys (kilometre to hundreds of kilometres). The soil C distribution of two sub-arctic sites in contrasting climatic, landscape/geomorphologic and vegetation settings has been described and analysed. The transition between birch forest and tundra heath in the Abisko (Swedish Lapland) field site, and the transition between mire and birch forest in the Kevo (Finnish Lapland) field site span several vegetation categories and landscape contexts. The natural variability of below-ground C stocks (excluding coarse roots > 2 mm diameter), at scales from the centimetre to the kilometre scale, is high: 0.01 to 18.8 kg C m-2 for the 0 - 4 cm depth in a 2.5 km2 area of Abisko. The depths of the soil profiles and the soil C stocks are not directly linked to either vegetation categories or Leaf Area Index (LAI), thus vegetation properties are not a straightforward proxy for soil C distribution. When mapping soil or vegetation categories over large areas, it is usually necessary to aggregate several vegetation or soil categories to simplify the output (both for mapping and for modelling). Using this approach, an average value of 2.3 kg C m-2 was derived both for soils beneath treeless areas and forest understorey. This aggregated value is potentially misleading, however, because there is significant skew resulting from the inclusion of exposed ridges (with very low soil C stocks) in the ‘treeless’ category. Furthermore, if birch trees colonise tundra heath and other ‘open’ plant communities in the coming decades, there will likely be substantial shifts in soil C stocks. This will be both due to direct climate effects on decomposition, but also due to changes in above- and below-ground C inputs (both in quantity and quality) and possibly changes in so-called root ‘priming’ effects on the decomposition of existing organic matter. A model of soil respiration using parameters from field surveys shows that soils of the birch forest are more sensitive to increases in mean annual temperature than soils under tundra heath. The heterogeneity of soil properties, moisture and temperature regimes and vegetation cover in ecotone areas means that responses to climate change will differ across these landscapes. Any exercise in upscaling results from field surveys has to indicate the heterogeneity of vegetation and soil categories to guide soil sampling and modelling of C cycle processes in the Arctic.