Long-term analysis of sap flow conditions in the trunk of Scots pine (Pinus sylvestris L.) in the old-growth phase in relation to air temperature

Studies on sap flow in the trunk of Scots pine were conducted in old-growth stands in the areas of strict protection
in the Kampinos National Park (Poland). The study’s main objective was to determine the changes in sap flow in the
pine trunk in correlation with the changing temperature measured under the canopy of the stand. Sensors were attached to the trees selected for the study at a height of 2 m above the ground to record the sap flow in the trunk and
the temperature under the canopy of the stand.
Based on the statistical models used and the analyses carried out, it was found that there was a high correlation
(0.913) between air temperature and sap flow in the tree trunk. The highest flow dynamics occurred at an average
daily temperature of 8.36°C. Below –5°C, the flux value began to approach the minimum values and disappeared.
At temperatures around 30oC, the trees reached maximum flow rates, which can be attributed to the physiological
characteristics of the trees. The photosynthetic processes taking place in Scots pine continue as long as the light and
temperature conditions are appropriate, which was evident in the flow rates recorded in all seasons. The method used
to measure sap flow in the tree trunk allows a thorough analysis of the physiological activity of the tree throughout
the year.