Temperature is commonly suggested to be the most important regulating factor for the position of the treeline. But also other abiotic and biotic processes may influence. To understand treeline shifts, it is necessary to improve the knowledge about the treeline forming species and their establishment, growth and survival. What are the drivers behind the shifts? The abundance of other vegetation is previously reported to facilitate growth of seedlings above treeline and also warmer temperatures are commonly observed to improve growth.   This study observed growth of mountain birch seedlings during one growing season. The relative importance of environmental factors in relation to the amount of growth and abundance was investigated. The study was conducted in the area of Abisko, Northern Sweden, using 4 sites, where transects were established just above the treeline. The sites differed in the amount of mean precipitation and aspect of the slopes. The vegetation composition around the seedlings and at the average treeline was observed, soil temperatures measured and the aspect of the slope estimated   Seedling growth was observed at all sites, with the highest amount in the sites with most precipitation, Pålnoviken and Katterjåkk. The observed soil mean and maximum temperatures were consistently highest in the southern facing slopes of Jiebrenjåkk and Pålnoviken. The vegetation was mostly dominated by dwarf shrubs, herbaceous plant cover, mosses and bare ground, and did not differ between the seedlings and the average treeline. The best model for growth was found to be the combination of the factors site, herbaceous plant cover, litter and soil mean temperature. Herbaceous plant cover was observed to improve the amount of growth in the drier sites of Pålnoviken and Jiebrenjåkk.   The finding of mountain birch seedlings growing in all vegetation types along the treeline, indicates that they have no preference of vegetation type for establishment. However, the negative influence of bare ground on growth supports the theory that abundance of vegetation facilitates growth of seedlings. The highest amount of growth was found in the sites with most precipitation, suggesting this to be an important factor for growth. In contrast to the expectations, warmer soil temperatures and the south facing slopes did not affect growth positively. This could be explained by the extremely high temperatures of the summer that may have induced drought. Finally, the improved growth by herbaceous plant cover in the drier sites may be because of their preference of moisture and nutrient rich soils, that could also support the growth of mountain birch seedlings.

No description available.

Diss. (sammanfattning) Uppsala : Univ., 2005. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Felipe Voloch. Vita. Includes bibliographical references. Also available from UMI.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2005. / Appendix includes papers co-authored with others. Includes bibliographical references. Issued also electronically via World Wide Web in PDF format; online version lacks appendix.

The use of alkali and alkaline earth metals as reducing agents in liquid ammonia solvent for aromatic and conjugated systems has been investigated by chemists at least since the early 1900's, e.g., Lebau and Picon (1). By subsequent additions of a proton source, the system yielded the first successful partial reduction of a monobenzenoid system, as reported by Wooster and Godfrey (2), in 1937. As a result of that success a patent was issued to Wooster for the process (3). Little additional work was reported until Birch and his co-workers picked up the investigation in the early 1940's. It was through his vigorous study and development of this reduction system that Birch's name came to be associated with reductions of organic compounds by alkali metals in liquid ammonia, hence, the Birch reduction. In this thesis the Birch reduction of cinnamic acid is investigated.

It has been previously shown that benzenesulfonamide gives thiophenol and diphenyldisulfide upon Birch reduction. The sulfonamide group is easily reduced. Probably the electron deficient sulfur atom in sulfonamide can accommodate an electron easily. The present study involved the Birch reduction of benzenesulfonamide, N,N-dimethylbenzenesulfonamide, N,N-diisobutylbenzenesulfonamide and 2-mesitylenesulfonamide.

This thesis is (1) an investigation in the identity of the unknown material Qazi (20) obtained when benzamide was reduced at the boiling point of ammonia with 3.3 equivalents of sodium and ethanol, (2) characterization of the components of the brown liquid obtained when m-methoxybenzamide was reduced with a large excess of sodium (8 equivalents of more), and (3) characterization of the compound formed when the latter is subjected to sudden heat.

No description available.

No description available.