The development of spruce forest on raw humus sites in Northern Finland and its ecology

Abstract

This very comprehensive study, based on the author's own researches as well as the literature (465 refs) is in two parts: (1) The development of Spruce forest on raw-humus sites in northern Finland [Cajander's HMT sites], and (2) The effect of the stands on microclimate and soil. In part 1, the author distinguishes two main types of stand, (a) primary, originating after fire, and (b) secondary, originating by natural regeneration from (a). Stand development (density, diameter distribution, height, volume distribution, mortality, and natural regeneration), development of associated vegetation, changes and development of root systems, and accumulation of raw humus, are described and discussed for both types. Birch plays an important part in the development of (a), diminishing as the stand ages; (b) stands are almost pure Spruce. The superiority of (a) over (b) in mean height, stand volume, and total production, is maintained throughout and the accumulation of raw humus is much greater under (b) than under (a). Part 2, largely based on the author's researches, deals with changes in illumination, temperature, wind velocity, snow melt, interception, and air humidity within the stand as it develops, and effects of stand development on soil moisture (with an investigation of transpiration by Birch and by Spruce), soil aeration, soil temperature, nutrient contents and acidity of soil, and development of CO2. In all these respects, the relatively more beneficial influence of Birch was confirmed. The practical applications of these findings are discussed and it is concluded that the restoration of the northern Spruce forests to their primary condition can be most simply and quickly effected by clear felling, burning over, and artificial regeneration. The deciduous seedling stand that will develop naturally on the burnt-over areas should be left until the planted Pine or Spruce is thinned, and at thinning a slight admixture of deciduous trees should be retained wherever competitive conditions permit. It is recommended that, wherever possible raw-humus Spruce stands should be converted to Pine.