Würzburg, Universiẗat, Diss., 2008.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Aug. 26,2009). Includes bibliographical references.

Zugl.: Kiel, Universiẗat, Diss., 2004.

The intent of this study is to describe and analyze the interrelations of vegetation and environment in the east-central sector of the Mackenzie River Delta, Northwest Territories. It traces the sequence and function of the allogenic events which create varying habitat systems and determines whether environmental modification, once initiated on terra nova is directional - in either a physical or floristic expression. In determining the sequence and influence of physical environmental factors, the following parameters were measured, employing standard instruments and field investigation techniques: micro-relief; depth, areal extent, and duration of flooding; thickness, areal extent, and particle-size distribution of annual deposits of alluvium; magnitude and significance of erosion; patterns of microclimatic variation (including air temperature and humidity, evaporativity, precipitation, wind speed, solar radiation, and net radiation); lake and channel temperatures; soil pH, moisture (hygrotope class), and temperature; development of varying active layer depths; and freezeback of the active layer. To analyze the vegetation of the study area, the phytosociologic methods of the Braun- Blanquet (Zurich-Montpellier) school were applied. Nine seral associations and the climax ecosystem were studied; each was fitted into a successional category. Plant succession was analyzed by reconstructing the course of vegetative development from pioneer to climax community with the aid of successional transects. Results of this study indicate that environmental and floristic changes in the Mackenzie Delta are directional - that given the formation of new ground, such as on the slipoff slope of a shifting channel, ecologic variation will follow a predictable direction. As the seral sequence advances, autogenic influences become dominant over the allogenic initiators until in the climax association, relatively steady-state conditions of environment and vegetation are attained. / Arts, Faculty of / Geography, Department of / Graduate

Memoria para optar al Título Profesional de: Ingeniero en Recursos Naturales Renovables / En las últimas décadas, se ha observado un calentamiento a nivel global que ha afectado la dinámica ecosistémica en uno de los biomas más frágiles e importantes del mundo, la tundra ártica. Se han observado variaciones significativas en la cobertura de vegetación, las masas de hielo marino, la temperatura de superficie terrestre y otros elementos en la zona ártica. Para determinar la magnitud de los cambios ocurridos en la tundra ártica, esta investigación se centra particularmente en las variaciones de la cobertura vegetal y la temperatura de superficie terrestre, a partir del análisis no paramétrico de las tendencias de la temperatura de superficie terrestre (LST) y el Normalized Difference Vegetacion Index (NDVI) de MODIS en el periodo 2000-2012. Este análisis se realizó distribuido espacialmente en la tundra ártica y también de forma discreta en las subzonas bioclimáticas del Circumpolar Arctic Vegetation Map (CAVM). Adicionalmente, se analizaron los datos de Reanalysis de temperatura de superficie y temperatura del aire de ERA-Interim. Los resultados mostraron que la tundra ártica ha experimentado un importante incremento de la temperatura de superficie terrestre en gran parte de la superficie, principalmente en las zonas más septentrionales, con tasas de incremento mensuales mayores a 1,1°C por década. Al mismo tiempo el NDVI también ha mostrado incrementos de 0,003 unidades por década en la tundra ártica, pero no estadísticamente significativos (p-valor > 0,05). En las distintas escalas temporales de análisis, se obtuvo como resultado que al oeste de Alaska ocurrió el enfriamiento más importante en la última década, de la misma forma como se observó una importante disminución de NDVI en el mismo periodo. El análisis en conjunto de MODIS y ERA-Interim permitió establecer un reciente calentamiento de la tundra ártica, más acelerado que las últimas tres décadas y acentuado en las zonas más frías y septentrionales del área de estudio. Se concluye que los resultados de esta investigación serán importantes para entender en qué medida la tundra ártica responde al escenario actual de cambio climático. / In the last decades, global warming has affected the eco-systemic dynamics in one of the most important and fragile biomes of the world, the arctic tundra. Significant changes have been observed in vegetation cover, sea ice cover, land surface temperature and other elements over the Arctic in the last decade. To determine the magnitude of changes in arctic tundra, this research is particularly focused on the variations of vegetation cover and land surface temperature, from the non-parametric analysis trends of Land Surface Temperature (LST) and the Normalized Difference Vegetation Index (NDVI) from MODIS, for the period 2000-2012. This analysis was performed spatially distributed in arctic tundra and discreetly in bioclimatic subzones of Circumpolar Arctic Vegetation Map (CAVM). Additionally, Reanalysis data of surface temperature and air temperature from ERA-Interim was analyzed. Results revealed that the arctic tundra has experienced a significant increase in the Land Surface Temperature on most of the area that it covers, principally in the high latitude areas with monthly increase rates higher than 1.1°C per decade, while the NDVI has also shown an increase of 0.003 units per decade in the arctic tundra, but not statistically significant (p–value < 0.05). In the different time scales of analysis, was obtained that the most important cooling occurred in the last decade was in the west of Alaska, in the same way a significant decrease in NDVI for the same period was observed. The pooled analysis of MODIS and ERA-Interim allowed to establish a recent warming trend of the arctic tundra faster than the last three decades and pronounced in colder and northern areas of the arctic tundra. It is concluded that the results of this research will be important for understanding to what extent the arctic tundra responds to the current state of climate change.

The tundra is currently warming twice as rapidly as the rest of planet Earth, which is thought to be leading to widespread vegetation change. Understanding the drivers, patterns, and impacts of vegetation change will be critical to predicting the future state of tundra ecosystems and estimating potential feedbacks to the global climate system. In this thesis, I used plant traits - the characteristics of individuals and species - to investigate the fundamental structure of tundra plant communities and to link vegetation change to decomposition across the tundra biome. Plant traits are increasingly used to predict how communities will respond to environmental change. However, existing global trait relationships have largely been formulated using data from tropical and temperature environments. It is thus unknown whether these trait relationships extend to the cold extremes of the tundra biome. Furthermore, it is unclear whether approaches that simplify trait variation, such as the categorization of species into functional groups, capture variation across multiple traits. Using the Tundra Trait Team database - the largest tundra trait database ever compiled - I found that tundra plants revealed remarkable consistency in the range of resource acquisition traits, but not size traits, compared to global trait distributions, and that global trait relationships were maintained in the tundra biome. However, trait variation was largely expressed at the level of individual species, and thus the use of functional groups to describe trait variation may obscure important patterns and mechanisms of vegetation change. Secondly, plant traits are related to several key ecosystem functions, and thus offer an approach to predicting the impacts of vegetation change. Notably, understanding the links between vegetation change and decomposition is a critical research priority as high latitude ecosystems contain more than 50% of global soil carbon, and have historically formed a long-term carbon sink due to low decomposition rates and frozen soils. However, it is unclear to what extent vegetation change, and thus changes to the quality and quantity of litter inputs, drives decomposition compared to environmental controls. I used two common substrates (tea), buried at 248 sites, to quantify the relative importance of temperature, moisture and litter quality on litter decomposition across the tundra biome. I found strong linear relationships between decomposition, soil temperature and soil moisture, but found that litter quality had the greatest effect on decomposition, outweighing the effects of environment across the tundra biome. Finally, I investigated whether tundra plant communities are undergoing directional shifts in litter quality as a result of climate warming. Given the importance of litter quality for decomposition, a shift towards more or less decomposable plant litter could act as a feedback to climate change by altering decomposition rates and litter carbon storage. I combined a litter decomposition experiment with tundra plant trait data and three decades of biome-wide vegetation monitoring to quantify change in community decomposability over space, over time and with warming. I found that community decomposability increased with temperature and soil moisture over biogeographic gradients. However, I found no significant change in decomposability over time, primarily due to low species turnover, which drives the majority of trait differences among sites. Together, my thesis findings indicate that the incorporation of plant trait data into ecological analyses can improve our understanding of tundra vegetation change. Firstly, trait-based approaches capture variation in plant responses to environmental change, and enable prediction of vegetation change and ecosystem function at large scales and under future growing conditions. Secondly, my findings offer insight into the potential direction, rate and magnitude of vegetation change, indicating that despite rapid shifts in some traits, the majority of community-level trait change will be dependent upon the slower processes of migration and species turnover. Finally, my findings demonstrate that the impact of warming on both tundra vegetation change and ecosystem processes will be strongly mediated by soil moisture and trait differences among vegetation communities. Overall, my thesis demonstrates that the use of plant traits can improve climate change predictions for the tundra biome, and informs the fundamental rules that determine plant community structure and change at the global scale.

This diploma thesis deals with the decomposition of fungal necromass in the Arctic tundra (Svalbard archipelago) under the factor of climate change (simulated by an increased temperature inside the Open Top Chamber). The dynamics of fungal necromass decomposition of two selected fungi, which differ in the level of melanin content and in C:N ratio - Laccaria laccata (hyaline, lower C:N ratio) and Phialocephala fortinii (melanized, higher C:N ratio), was compared. The aim of the work was to evaluate the influence of melanization level of fungal necromass and elevated temperature on the dynamics of fungal necromass decomposition and on the community composition of the decomposers (fungi, bacteria). The experiment focused on monitoring the dynamics of fungal necromass decomposition, changes in enzyme activity, changes in melanin content and C:N ratio during decomposition, as well as on the analysis of the microbial community composition on decomposing mycelium. Throughout the whole incubation, the necromass of P. fortinii decomposed more slowly than the necromass of L. laccata. The differences in the dynamics of decomposition were mainly due to the biochemical composition of the fungal necromass (C:N ratio and melanin content). The melanin content increased in both types of mycelium during...

Climate change is expected to have a large impact on northern ecosystems. Increased temperatures and altered precipitation and snow cover patterns will have a great impact on subarctic tundra. Bryophytes form an important component of tundra ecosystems because of their high abundance and their importance in many ecological processes. The effect of elevation and snow cover on freezing damage in shoots of three subarctic bryophytes: Ptilidium ciliare, Hylocomium splendens and Sphagnum fuscum, was studied in a snow manipulation field experiment at different elevations in Abisko, Sweden, during early spring. The treatments included snow addition, snow removal and control. In addition, bryophyte healthiness at the plot scale was determined by image analysis using colour selection, and soil temperature and moisture data were collected. Freezing damage differed significantly among bryophyte species with P. ciliare having the lowest freezing damage. There was a decrease in freezing damage over time due to the increase in temperature as spring progressed. Counter expectation, freezing damage was higher at low elevation although the mean daily minimum temperature was lower at higher elevation, which might be due to adaptation effects. Snow treatment had only a minor effect on freezing damage, but it did have an effect on proportion of undamaged tissue at the plot scale which increased with increasing snow cover at high elevation, but decreased with increasing snow cover at low elevation. Soil moisture content was also affected by snow treatment. The number of freeze-thaw cycles was less for S. fuscum and H. splendens compared to bare soil plots, which indicates insulating capacities of these bryophytes. Freezing damage could not be explained by the measured climate variables alone; therefore, it is likely the result of a complex set of factors, possibly including solar radiation and disturbance by herbivores.

Rapid climate change in Arctic regions is of concern due to important feedbacks between the Arctic land surface and the global climate system. A large amount of organic carbon (C) is currently stored in Arctic soils; if decomposition is stimulated under warmer conditions additional release of CO2 could result in an accelerating feedback on global climate. The strength and direction of Arctic C cycle - climate feedbacks will depend on the growth response of vegetation; if plant growth increases some or all of the extra CO2 emissions may be offset. Currently the Arctic is thought to be a small net sink for CO2, the expected balance of terrestrial C sinks and sources in the future is unknown. In this thesis I explore some of the critical unknowns in current understanding of C cycle dynamics in Arctic vegetation. Quantifying gross primary productivity (GPP) over regional scales is complicated by large spatial heterogeneity in plant functional type (PFT) in Arctic vegetation. I use data from five Arctic sites to test the generality of a relationship between leaf area index (LAI) and canopy total foliar nitrogen (TFN). LAI and TFN are key drivers of GPP and are tightly constrained across PFTs in Low Arctic Alaska and Sweden, therefore greatly simplifying the task of up-scaling. I use data from Greenland, Barrow and Svalbard to asses the generality of the LAI-TFN relationship in predicting GPP at higher Arctic latitudes. Arctic ecosystems are unique among biomes in the large relative contribution of bryophytes (mosses, liverworts and hornworts) to plant biomass. The contribution of bryophytes to ecosystem function has been relatively understudied and they are poorly represented in terrestrial C models. I use ground based measurements in Northern Sweden to fill an existing data gap by quantifying CO2 fluxes from bryophytes patches in early spring and summer, and develop a simple model of bryophyte GPP. Using the model I compare bryophyte GPP to that of vascular plants before, during and after the summer growing season, finding that productive bryophyte patches can contribute up to 90 % of modelled annual GPP for typical vascular plant communities at the same site, and that the relative magnitude of bryophyte GPP is greatest in spring whilst the vascular plant canopy is still developing. Understanding how GPP relates to plant growth is important in relating remotely sensed increases in Arctic ‘greenness’ to changes in plant C stocks. I use a 13C pulselabelling techniques to follow the fate of recently fixed C in mixed vascular and bryophyte vegetation, with a focus on quantifying the contribution of bryophytes to ecosystem carbon use efficiency (CUE). I show that bryophytes contribute significantly to GPP in mixed vegetation, and act to increase ecosystem CUE. I highlight the importance of including bryophytes, which do not have roots, in aboveground: belowground partitioning schemes in C models. To further explore C turnover in bryophytes, I use the results of a second 13C labelling experiment to develop a model of C turnover in two contrasting Arctic mosses (Polytrichum piliferum and Sphagnum fuscum). I find significant differences in C turnover between Polytrichum piliferum which respires or translocates about 80 % of GPP, while Sphagnum fuscum respires 60 %. This analysis is the first to explicitly model differences in C partitioning between Arctic bryophyte species. Finally, I discuss the implications of each chapter for our understanding of Arctic C dynamics, and suggest areas for further research.

Observational and modelling studies show that the warming of the Arctic is leading to shrub expansion. This shift in vegetation cover is expected to significantly alter the distribution of snow across the landscape and the interactions between the land surface and the atmosphere. Shrubs capture wind-blown snow, increasing snow depth and decreasing winter water loss through sublimation, and bend beneath the weight of snow, affecting albedo. Snow is highly insulative and affects the soil hydrological and thermal properties. Therefore, as the snow-vegetation-soil interactions is expected to be at the core of feedback loops leading to further shrub expansion, there is a need for models to be able to simulate these processes accurately. Initially using the community land surface model JULES (Joint UK Land Environment Simulator) this study investigates the effects of shrub-tundra on snow and runoff. Alternative formulations of soil processes are proposed, which are better adapted to the representation of subgrid heterogeneity in cold regions than the current model formulation, and evaluated over the Abisko and Torne-Kalix river basins. In addition, a high resolution shrub bending model, which calculates the exposed winter shrub fraction, is developed and parameterised for use alongside the snow cover parameterisation in JULES in order to provide a better representation of shrub-specific processes. This revised JULES more than doubles the efficiency coefficient and halfs the negative bias between modelled and observed runoff in the shrub-tundra Abisko basin. However, the current structure of the model is found to be inadequate for use in investigating the effect of shrub-tundra expansion because it calculates a single energy balance for the snow-free and the snow-covered areas. To address this issue, a distributed three-source (snow-shrub-ground) model (D3SM) is developed. D3SM is evaluated against snow and energy ux measurements from a shrub-tundra basin in the Yukon, Canada, and is found to reproduce snowmelt energetics well. The effects of shrub expansion on the energy balance of the basin during snowmelt are then investigated by increasing the vegetation fraction and canopy height of the current shrub distribution, which is found to be positively correlated with topography. D3SM shows that the most significant effects of shrub expansion in the basin are to reduce the spatial variability of snow depth and to increase the sensible heat flux from the surface to the atmosphere.