Estimating herbivore density is an important part of understanding their impact on vegetation.  Many studies have been carried out on the impact of reindeer and other herbivores on arctic and sub-arctic vegetation, but they are difficult to compare as they typically use different methods to estimate herbivore activities.  The aim of this study was to compare three methods that were based on the recent International Tundra Experiment herbivory protocol to measure the activities of three herbivore groups: reindeer, rodents and invertebrates. The robustness of the methods themselves was then evaluated.  Fieldwork was carried out at 12 sites in the Fennoscandian mountain area, with controls inside reindeer exclosures.  The results showed that the methods were the most robust when measuring reindeer activities.  The reindeer measurements were also well correlated with a reindeer-density estimate calculated from official reindeer population data.  This study recommends considering the use of photographs to increase the time-efficiency of pellet-counts.  The rodent activity estimates were good, but the patterns inside exclosures differed to the patterns outside exclosures.  The results for invertebrates were deemed to be less reliable as the measurements for one method were not recorded at an appropriate scale.  In conclusion, the findings of this study will help improve the comparability of future studies on the impact of reindeer herbivory and other herbivores, and gives suggestions for more accurate ways of measuring herbivore pressure in arctic and sub-arctic vegetation.

Craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100-1000Ma time scales. Here we show that the Fennoscandian Shield in southeastern Sweden experienced several episodes of burial and exhumation from similar to 1800Ma to the present. Apatite, titanite, and zircon (U-Th)/He ages from surface samples and drill cores constrain the long-term, low-temperature history of the Laxemar region. Single grain titanite and zircon (U-Th)/He ages are negatively correlated (104-838Ma for zircon and 160-945Ma for titanite) with effective uranium (eU=U+0.235xTh), a measurement proportional to radiation damage. Apatite ages are 102-258Ma and are positively correlated with eU. These correlations are interpreted with damage-diffusivity models, and the modeled zircon He age-eU correlations constrain multiple episodes of heating and cooling from 1800Ma to the present, which we interpret in the context of foreland basin systems related to the Neoproterozoic Sveconorwegian and Paleozoic Caledonian orogens. Inverse time-temperature models constrain an average burial temperature of similar to 217 degrees C during the Sveconorwegian, achieved between 944Ma and 851Ma, and similar to 154 degrees C during the Caledonian, achieved between 366Ma and 224Ma. Subsequent cooling to near-surface temperatures in both cases could be related to long-term exhumation caused by either postorogenic collapse or mantle dynamics related to the final assembly of Rodinia and Pangaea. Our titanite He age-eU correlations cannot currently be interpreted in the same fashion; however, this study represents one of the first examples of a damage-diffusivity relationship in this system, which deserves further research attention.

Afin d’étudier les changements hydrologiques passés du « lac Noir » (dernière phase lacustre de la mer Noire) et l’expression de la Dernière Déglaciation en Europe centrale, des techniques analytiques variées ont été mises en œuvre sur la carotte MD04-2790 : modélisation, développement de méthodes statistiques, géochimie élémentaire et isotopique. La reconstitution de l’évolution des âges réservoir du « lac Noir » au cours des 30 derniers millénaires a permis de mieux comprendre les réponses hydrologiques du bassin aux changements climatiques (variations du niveau du plan d’eau, phases de stratification, possible déstabilisation d’hydrates de gaz). L’âge de la dernière reconnexion du « lac Noir » avec la mer Méditerranée a été révisé à 9 000 ans BP. L’interprétation des isotopes du Nd en termes de provenance des sédiments a permis de mettre en évidence que les pulses d’eaux de fonte arrivant dans le « lac Noir » au cours de l’événement de Heinrich 1 provenaient de la désintégration de la calotte fennoscandinave. Un mécanisme régional d’interactions climatiques entre lacs proglaciaires et atmosphère a été proposé pour expliquer l’organisation temporelle particulière des pulses d’eaux de fonte. Nos résultats renforcent le paradigme de Denton qui suggère que des stades prolongés sont nécessaires au passage du mode climatique glaciaire au mode interglaciaire. / In order to study the past hydrologic changes of the Black Sea “Lake”, various analytical techniques were applied to study the core MD04-2790: modelling, development of statistical approaches, elemental and isotopic geochemistry. The reconstructed reservoir age changes of the Black Sea “Lake” were interpreted in terms of the hydrologic responses of the lake to glacial/deglacial climate changes (water level change, water column stratification, possible chlatrate dissociation). Calendar age of the Black Sea “Lake” last reconnection to global ocean was also revised to 9,000 yr BP. Finally, drastic changes in εNd values strongly suggest that sediments deposited in response to Deglacial Water Pulses (DWP) during Heinrich Event 1 (HE1) originated from the Fennoscandian Ice Sheet (FIS), providing the first direct evidence that the Black Sea “Lake” recorded the collapse of the FIS. The peculiar temporal organisation of DWPs suggests outbursts of proglacial lakes into Dniepr catchment as well as regional climatic interactions between proglacial lakes and atmosphere. The HE1-timing of the DWPs occurrence would indicate that FIS was involved in the N-Atlantic circulation reduction that shifted Earth climatic machine towards interglacial conditions in accordance with Denton’s paradigm.

Research Doctorate - Doctor of Philosophy (PhD) / The original contribution of this thesis is to demonstrate the use of a generalised and parsimonious approach to building individual-based computer models of ecological systems with the objective of advancing our mechanistic understanding of these systems. Two models are presented; the first, a model of predator-prey interaction, produces the expected non-linear dynamics and illustrates the importance of the timing of variable updating and individual variation for the persistence of the populations. This model is applied to two near-exclusive, cycling predator-prey systems, those of the Canadian lynx and snowshoe hare and the Fennoscandian mustelid predators and their microtine prey. The reproduction of the patterns found in the empirical data of these systems by the model suggests that the underlying mechanism of these predator-prey systems may be more simple than is suggested by other more complex models reported in the literature. The second model describes a system similar to that of a grazing herbivore in a two-dimensional space. The emergence of complex behaviour resulting from the use of space in the model, including metapopulation-like local extinction and re-population and the effects of corridors and edge qualities on the species are demonstrated. The inclusion of a graphical display of the two-dimensional space in the computer interface to the model reveals important details of system behaviour not evident in the population means, including herding behaviour. The latter is dependent on herbivore mobility and the re-growth of resources in an heterogeneous environment, and emerges in the absence of social behaviour. The problem of detecting herding behaviour automatically is addressed, including the development of qualitative and quantitative definitions of herding in the model.