The rare and elusive wood-living beetle Tragosoma depsarium, once widespread all over Sweden, is associated with large, sun-exposed pine logs required for breeding. Due to modern forestry and fire suppression, this type of substrate has become so rare in the landscape that the beetles’ existence in Sweden is threatened. Recently, the female sex pheromone of this species was synthesised, providing a new method to monitor beetle populations using pheromone traps. Such a method was used in the current study to relate the presence-absence of T. depsarium with different landscape variables at different scales; 100, 500, 1000 and 2000 meters, respectively. The occurrence of T. depsarium in Östergötland County was associated with the amount of protected areas and clear-cuts at 500 and 1000 meters, respectively. Additionally, the amount of pine forest within 2000 m from the trap showed a weak, positive effect on the number of beetles. In the whole south-east boreo-nemoral zone of Sweden, a positive correlation between beetle occurrence and protected areas were found at 2000 m together with a negative correlation for volume pine wood within 100 m. Also, emergence holes on pine logs around each trap were strongly associated with beetle occurrences. To conclude, using pheromone traps were an easy way of detecting beetles. Although the number of caught T. depsarium varied greatly over time, the sampling period matched the flight period well. For long-term survival of this beetle, the forests must contain breeding substrates and be opened up through prescribed burning, selective cutting and active forestry.

The hemlock-silverbell (Tsuga canadensis-Halesia tetraptera) forest type is known to exist in only two places, the Great Smoky Mountains National Park (GRSM) and the Joyce Kilmer National Memorial Forest. The hemlock component of this forest type is currently threatened by the hemlock woolly adelgid (Adelgis tsugae), an invasive aphid-like insect native to Japan. This current status has given rise to the need to investigate the ecological resources of this rare forest type before the hemlock component dies out. The objectives of this study were to determine the nature of the plant/environment and plant/plant associations within this forest type. Within this forest type hemlock was negatively related to protection, aspect, and slope steepness and silverbell was positively related to aspect and slope steepness. This study also identified some interspecific associations such as the negative relationship in the understory between hemlock and striped maple, and provided evidence that understory stems are exhibiting a growth response to hemlock decline in these stands. The information obtained from this study characterizing the plant/environment interactions and even the structural and species components of this forest type will serve as a baseline of data from which to measure change and will provide insight into the mechanisms of species distribution and perhaps into short term scenarios of forest response to hemlock decline and mortality.

The spatial patterns of land surface and subsurface characteristics determine the spatial heterogeneity of hydrological processes. Soil depth is one of these characteristics and an important input parameter required by distributed hydrological models that explicitly represent spatial heterogeneity. Soil is related to topography and land cover due to the role played by topography and vegetation in affecting soil-forming processes. The research described in this dissertation addressed the development of statistical models that predict the soil depth pattern over the landscape; derivation of new topographic variables evaluated using both serial and parallel algorithms; and evaluation of the impacts of detailed soil depth representation on simulations of stream flow and soil moisture. The dissertation is comprised of three papers. In paper 1, statistical models were developed to predict soil depth pattern over the watershed based on topographic and land cover variables. Soil depth was surveyed at locations selected to represent the topographic and land cover variation at the Dry Creek Experimental Watershed, near Boise, Idaho. Explanatory variables were derived from a digital elevation model and remote sensing imagery for regression to the field data. Generalized Additive and Random Forests models were developed to predict soil depth over the watershed. The models were able to explain about 50% of the soil depth spatial variation, which is an important improvement over the soil depth extracted from the SSURGO national soil database. In paper 2, definitions of the new topographic variables derived in the effort to model soil depth, and serial and Message Passing Interface parallel implementations of the algorithms for their evaluation are presented. The parallel algorithms enhanced the processing speed of large digital elevation models as compared to the serial recursive algorithms initially developed. In paper 3, the impact of spatially explicit soil depth information on simulations of stream flow and soil moisture as compared to soil depth derived from the SSURGO soil database has been evaluated. The Distributed Hydrology Vegetation Soil Model was applied using automated parameter optimization technique with all input parameters the same except soil depth. Stream flow was less impacted by the detailed soil depth information, while simulation of soil moisture was slightly improved due to the detailed representation of soil depth.

L'urbanisation croissante de ces dernières décennies nécessite une connaissance approfondie de la dynamique de la biodiversité en milieu urbain afin d’aider à la mise en place de politiques de développement urbain favorisant le maintien de cette biodiversité. Ce travail de doctorat a évalué l'homogénéisation taxonomique et la composition fonctionnelle des communautés de flore spontanée le long d’un gradient d’urbanisation en prenant comme unité d’étude le jardin privatif, ainsi que la structure génétique d’une espèce de plante, Parietaria judaica.L'homogénéisation taxonomique varie le long du gradient d’urbanisation. Les jardins privatifs des centres villes étudiés seraient moins riches, mais favoriseraient la diversité taxonomique au regard de la composition spécifique des communautés de par leurs expositions, aménagements et pratiques. L'étude des traits des communautés met en évidence des variations de la composition fonctionnelle le long du gradient d’urbanisation. Les zones de forte densité de bâti filtrent des traits, notamment liés à la dispersion et à la persistance des espèces. L'endozoochorie pourrait permettre le franchissement des bâtis qui entourent les jardins.Enfin, l’absence de structure génétique de Parietaria judaica à l’échelle locale des villes suggère des échanges génétiques quelle que soit la densité de bâti, tandis qu’une structure génétique marquée est observée à l’échelle régionale, entre les trois sites.Le jardin privatif qui à l’instar des autres habitats du milieu urbain, présentent des communautés végétales qui peuvent participer aux dynamiques de la végétation urbaine. / Increasing urbanization in recent decades requires a thorough understanding of the dynamics of urban biodiversity to aid in the establishing of urban development policies to promote the biodiversity. This doctoral work evaluated the taxonomic homogenization and functional composition of spontaneous flora communities along a gradient of urbanization taking as the unit of study the private garden, and the genetic structure of a plant species, Parietaria judaica.Taxonomic homogenization varies along the urbanization gradient. The private gardens of the centers studied cities are less rich but would enhance taxonomic diversity in terms of species composition of communities through their exposure, planning and practices.The study of traits communities highlights changes in the functional composition along the urbanization gradient. High built-up density areas filter traits, in particular linked to the dispersion and persistence of species. The endozoochorie could allow the crossing of built around the gardens.Finally, the lack of genetic structure of Parietaria judaica at local scale suggests genetic exchange regardless of the built-up density, while a significant genetic structure was observed at the regional level between the three sites.The private gardens, which like the other green patchs in urban areas, have plant communities that can participate in the dynamics of urban vegetation.