The Significance of Soil Conditions for Sap Flow of Scots Pine in the Boreal Environment

Abstract

Conifers growing at high latitude are seasonally subjected to freezing temperatures both in the air and soil. The depth and duration of soil frost as well as the persistence of low soil temperature varies spatially, influenced to a large degree by the snow cover distribution. Silvicultural practice affects the snow cover distribution and thus the dynamics of soil warming during spring. The importance of soil temperature for growth and vitality has been seen on seedlings and saplings in the laboratory. But we know very little about the effect of cold soils on larger trees in the field and the potential loss of forest production after a stand is established. The objective of this thesis was to examine the effects of soil conditions on sap flow during spring. Water dynamics were examined in the field on Scots pine trees (Pinus Sylvestris L.) exposed to different soil temperature regimes. One attempt to quantify the sensitivity of tree water use to soil and atmospheric conditions in the boreal forest environment was made by manipulating the soil thermal regimes on treescale soil plots. Soil temperature, soil moisture content, snow and frost depth as well as above ground climatic parameters were measured, together with sap flow, needle water potential, stem increment and shoot elongation. In this study, low soil temperatures restricted tree water uptake most after the growing season had started. Before the start of the growing season, low soil temperatures bad little apparent effect. Liquid water existed in the soil as soil frost successively thawed and snowmelt infiltrated. Water, however, was not available to the tree until the soil temperature in the upper rooting zone bad reached a threshold temperature above 0°C, even if the evaporative demand was large due to above ground climatic conditions. The study has confirmed the importance of low soil temperatures for tree water uptake when soil warming is delayed beyond the start of the growing season, as defined by air temperatures. Another approach to elucidating the effect of soil conditions on tree water uptake was to compare the above and below ground climate at a forest edge with that of the forest interior. Differences in tree water uptake and stem increment were found that could be associated with the difference in soil thermal regimes associated with the forest edge. The estimated water use was larger at the edge zone than in the stand interior. The results of both field studies suggest that the effect of soil temperatures on tree water uptake during spring, in conjunction with above ground conditions, is a factor to consider in forest management in areas susceptible to soil frost and low soil temperatures.

Published in

Rapport / Sveriges lantbruksuniversitet, Miljöanalys
2001, number: 2001:2
Publisher: Institutionen för miljöanalys, Sveriges lantbruksuniversitet

SLU Authors

• Mellander, Per-Erik

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Forest Science
Soil Science

Permanent link to this page (URI)

https://res.slu.se/id/publ/132746