Temporal Variation of Evapotranspiration and Growth in Finnish Forest in Relation to Climate

• Main Author: Reijo Solantie
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2006
• Subjects: Arctic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.539.1906; http://www.geophysica.fi/pdf/geophysica_2006_42_1-2_035_solantie.pdf

In the boreal zone, the annual amounts of evapotranspiration in forests Ef (mma–1) and the growth of growing stands G (m–3ha–1a–1) are practically determined by climate; the spatial variation of both of them can be largely explained by the effective temperature sum L (°Cd–1) and the maximum soil frost depth in winter F (cm); the latter, in its turn, is a function of snow depth and frost sum. In the southern boreal regions, particularly on sandy glacial tills, drought in early summer is also noticeable. This, which somewhat counterbalances the effect of L, was roughly estimated. The partial derivatives of G with respect to the effective temperature sum L and winter’s maximum soil frost depth F were approximated by those obtained earlier by the author from spatial analysis. Applying the relation between Ef and the volume of growing stands K as obtained by Hyvärinen et al. (1995) and the mean ratio G/K on the basis of forest inventories, as well as the derivatives of Ef with respect to L and F, the temporal standard deviations of G and Ef could be roughly approximated for various regions south of the Arctic Circle in Finland. The results were verified by the actual temporal standard deviations of G found in ring-width studies, and evaporation observed by the Class–A pan. The results of this study, albeit rough, were of the right magnitude. It was also shown that the mean snow depth during winter more affected the soil frost depth, Ef and G, than did the frost sum. The correlations between G and the precipitation during winter months, as well as between G and monthly mean temperatures, obtained by ring-width studies, agree well with the influence of snow depth and frost sum obtained in this study. Key words: variation of forest growth, variation of evapotranspiration, growth of boreal forests, evapotranspiration in boreal forests 1.