fulltext - DiVA

12 HUGO SJORSrainfall, and in winter water flow is extremely lowexcept in the south-west, where maxima in lateautumn or winter are usual. The difference in flowis exceedingly great in those northern rivers whichhave not yet been regulated, with about 50 to lOOtimes greater flow at high waters than at the latewinter minimum. This also leads to great amplitudesin water-level of rivers and lakes, in extremecases nearly 6 m difference between highest andlowest water-level.LocAL CLIMATE.-Little is known about localvariation of Swedish climate. Among importantfactors for vegetation, warmth of insolation andfrequency of low minimum temperatures at night(including frosts) are known to be much affectedby situation and exposure. It should be observedthat Sweden (especially the north) is at such a highlatitude that the difference in insolation betweenslopes towards the south and those facing west oreast is diminished; contrary to true Polar conditions,however, north-facing slopes are still highlyinferior. Data by JIM LuNDQVIST (see his contribution)and others seem to show that the mostimportant climatic feature of an elevated strongslope, when compared with a valley situation, isthe higher temperature during cool nights, perhapsalso the early melting of the snow cover in favourablyexposed steeps.Lakeside situations in the north are characterizedby lower frequencies of frosts but also by lowertemperatures on bright summer's days. In combinationwith direct influence of wind and scarcity ofprotecting snow in winter, this leads, in the uppersubalpine region, to an "inversion" of the tree lineon islets and on the shores of certain lakes, andalso on small hills of mineral soil protruding overlarge mires. Similar effects are probably partlyresponsible for the poor growth of several woodyspecies on the outer islets in the Baltic archipelagos,but the extremely late spring and other factorsmay also be of importance. The reducing effect onprecipitation of large bodies of water has alreadybeen mentioned; an opposite, increasing effect isdue to the forest which slows down the wind andthus forces the air to rise.As elsewhere, the micro climate deviates oftenstrongly from the general and local climate treatedin this article, but few data are available.SoURcEs.-Data on which this article was basedwere taken from several works, the chief source being"ATLAS OVER SVERIGE", which has legends and summariesin English . A large handbook for internationaluse is "A GEOGRAPHY OF NORDEN". Pre-Quaternarygeology is treated by N. H. MAGNUSSON et al. (1960) andthe Quaternary by G. LUNDQVIST (1959a, 1961). Thebook on North Swedish soils by 0. TAMM occurs inan English translation (1950) as well as the Swedishoriginal (1940). For the soils, see also a short paperin German by ScHLICHTING (1955). Among works inSwedish, special reference is made to MAGNUSSON,G. LuNDQVIST & REGNELL (1963), to P. H. LuNDE­GARDH, JAN LUNDQVIST and M. LINDSTROM (1964),and to articles by JAN LUNDQVIST and T. TROEDSSONin "JORD" (1963) for geology and soils, to ANG­STROM (1958) for climatology, and to AGER (1964)regarding winter climate of the northern part; butmaps are also found in HULTEN (1950), SELANDER(1955), various atlases and encyclopaedias etc. Complementarydata for special areas will be found inseveral articles in this book. - The author is indebtedto Dr. B. COLLINI of Uppsala University for adviceon geology.Acta Phytogeog1·. Suec. 50