Linking the measurement data of the substance flows of the SMEAR Estonia measuring station with the place of growth

The SMEAR Estonia is an important step towards understanding how forest ecosystem and the atmosphere affect each other. The station provides long-term continuously measured eddy-covariance CO2 flux data. Parameters such as wind speed and direction are not controllable by human, but forest management methods are, thus the flux tower helps to assess how human activities affect forest ecosystem-atmosphere relationship as well as to assess natural processes. In this study, the footprint for years 2015–2020 was calculated with Kljun model according to wind speed and direction. Measurements were taken from 30 m and 70 m height. Data was obtained by continuous high frequency (10 Hz) measurements by the eddy-covariance method and averaged over half-hour intervals. Results showed that the footprint area measured from 30 m over six-year period differed only by 5%. From 70 m this difference was only 1.2% over the six-year period. Average area for both 30 m and 70 m FFP was 61,5 ha and 4029,7 ha respectively. The growing stock of the forest was affected by forest management, but in general it grew by 3,2% for 30 m FFP. The main tree species growing in the area of the footprint are Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and Silver birch (Betula pendula) with some small amount of aspen and alder species. The dominant wind directions were ranging from west to south in 2015–2017 and in 2018–2020 from south-west to south-east. The footprint area is affected mainly by wind speed and direction, and by forest management activities like harvesting and clear-cutting. Such measurements help to understand how human activity and natural processes affect formation of the footprint.