Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2006. / Härtill 4 uppsatser.

Abstract Boreal urban forests are becoming more and more fragmented and, at the same time, are exposed to low-level but long-term nitrogen and sulphur deposition. Natural mid-boreal forests are dominated by few tree and shrub species, while herbs and grasses are rare. Soils in mid-boreal forests are rich in ectomycorrhizal (ECM) fungi, forming a symbiotic relationship with forest trees, which is important for the nutrient cycle especially in nutrient-poor ecosystems. Aims of this thesis were 1) to study differences between mid-boreal urban and rural forests in composition of macrofungi and structure of plant communities, 2) to explore whether responses of Scots pine seedlings to excess N are mediated via soil or via air, and 3) to study if partial removal of vegetation and humus layer alleviates the adverse effects of excess N on plant and fungal communities, and promotes performance and regeneration of Scots pine in urban forests. The growth responses of seedlings and their mycorrhizal colonization were studied in both field and greenhouse experiments. Peroxidase (POD) activity was used as a root stress indicator. Urban forests were poor in number of fruiting ECM fungal species, but rich in herbs and grasses in the field layer, as compared to rural forests. These differences were thought to result from changes in soil properties. ECM fungal colonization in Scots pine roots did not respond significantly to high nitrogen load in soil, but high root POD activity indicated changes in root physiology. ECM macrofungal diversity in urban forests was not markedly increased during a five-year survey after a partial humus removal treatment. On the other hand, fruiting of Cortinarius semisanguineus is a positive response to the treatment. Scots pine seedling emergence was poor due to rapid revegetation at the urban sites, but the treatment promoted both root and shoot growth of planted Scots pine seedlings in urban forests. Decreased root POD activity in Scots pine seedlings in the humus removal treatment possibly indicates lowered root stress. Soil manipulations may result in a risk of nutrient leakage, and a risk of invasion by non-typical plants. Also, small stand size with high recreation pressure causes a risk for tree regeneration in urban forest stands. These risks need to be considered when planning management of urban coniferous forests.

Abstract Mycorrhizal fungi are important contributors to the functioning of boreal forests, since they act in the bilateral carbon and nutrient transport between above- and belowground parts of the ecosystem. In ectomycorrhizal (ECM) symbiosis of woody host plants, both fungal and plant partners depend on resources provided by the other. A single tree may simultaneously host several ECM fungal partners, which greatly enhance the host's nutrient uptake. At the same time nearly 20% of host primary production is allocated to mycorrhizal fungi. Although fungi depend on host-derived carbon, it is poorly understood how reduced carbon availability, e.g., due to herbivory, affects the ECM fungal symbionts. In this thesis I studied the impact of simulated insect defoliation or mammal browsing on mycorrhizal fungi of boreal woody hosts. Quantitative and qualitative changes in biomass partitioning in different fungal compartments were detected. None of the experiments showed that defoliation or shoot clipping treatments reduced the intensity of ECM colonisation, while treatments often shifted fungal composition towards less biomass producing ECM morphotypes. Above- and belowground diversity in ECM symbionts tended to decrease due to shoot or foliar damage. In addition, in some cases defoliation also reduced fungal biomass in fine roots and decreased ECM sexual reproduction by reducing the number of sporocarps produced. Defoliation induced a similar response pattern in the host and in ECM fungi with a stronger response to increasing severity of treatment (e.g. degree of removed foliage or repeated years of defoliation). This was also confirmed when relating the effects of host and ECM fungal symbionts to defoliation using present and previously published data. The present results suggest that belowground adaptation of boreal trees to the changing environment is mediated by changes in fungal community or biomass partitioning. The lack of response in the intensity of ECM colonisation further emphasises the importance of the symbiosis to boreal trees.

Die exponierten Sandstein-Felsriffe im Nationalpark Sächsische Schweiz stellen einen Waldgrenzstandort dar. Erkenntnisse über das Baumwachstum unter diesen nährstoffarmen und trockenen Bedingungen können dazu beitragen, die Reaktionen normaler Bestände auf mögliche Klimaveränderungen besser vorherzusagen. Für die vorliegende Arbeit erfolgte die Anlage von insgesamt zwölf Versuchsflächen in den zwei Teilgebieten des Nationalparks Sächsische Schweiz, auf denen das Wachstum der Kiefern und die zuwachsbeeinflussenden Faktoren untersucht wurden. Die Auswertung der entnommenen Bohrspäne zeigt, dass Kiefern auch bei äußerst geringen Zuwachsraten jahrelang überleben können. Es wurden vielfach schmale Jahrringe aus lediglich zwei bis drei Zellreihen sowie Einzelbäume mit bis zu 29 vollständig ausgefallenen Jahrringen gefunden. Die Analyse der Zusammenhänge von Radialzuwachs, Höhenzuwachs, Bestandesdaten, Konkurrenzindizes, Standort- und Witterungsparametern nimmt einen großen Teil der Arbeit ein und mündet in der Darstellung entsprechender Wuchsmodelle.

Manufacturers of saw chains continuously strive to increase the performance of their products by reducing cutting times and minimising the energy consumption required for cutting. However, the evaluation process through testing is problematic as several uncontrollable factors impact the results. A large source of uncontrollable factors is the material used as a workpiece. Historically, wood has been used as a workpiece material since it is often what the end user will use it for. As a natural material, each stem contains a unique structure and can have a high variation in mechanical properties. Consequently, the analysis of older cutting efficiency is problematic since the result is linked to the specific stem being sawn, which is destroyed during the testing process. The current work aims to improve the repeatability of these tests by increasing the understanding of which material characteristics and material properties impact the variance during cutting efficiency measurements. An experiment was performed using pine as a workpiece material. It was found that the wood structure, density and hardness or moisture content could explain approximately 80% of the variation in the final tests. A more homogeneous material polyethylene was used to explore if a decrease in variation within these factors resulted in lower variance between cutting efficiency results. The variance between results was found to be lowest in pine when knots were excluded. The variance in polyethylene was slightly higher but showed promising evidence for being a suitable alternative material for long-term testing.