The Effects of Clear-Cutting a Hemiboreal Forest on Local CO2 Fluxes in Norunda, Sweden

As CO2 builds up in the atmosphere causing global climate change (IPCC, 2022) trees have become an international symbol of combatting this, and for good reason. Trees take up CO2 which as a result combats these changes, and when these trees are cut down fewer individuals remain to take up the CO2 that we humans emit (Chapin et al., 2011). This means that clear-cut areas don’t act as the carbon sinks they once were, for many years to come (Grelle et al., 2023; Peichl et al., 2022). If forestry and timber production is not done sustainably it results in an increase of CO2 in the atmosphere, which has global consequences (Chapin et al., 2011; Smith et al., 2021) if it is done on a large scale as it is today.. In this study the impact of clear-cutting a forest has on local CO2 fluxes was studied by comparing such fluxes between the years 2022 and 2023, one year prior to and one year after a complete clear-cut of a hemiboreal forest. It was investigated whether there were any changes in flux between the two years as well as whether any major spatial variation in flux was present. The chosen study site is a Swedish flux and exchange measurement station, Norunda, owned by the Swedish research agency ICOS. The study was performed by sorting CO2 flux data into eight sectors depending on the wind direction of the measurement. A simplified flux footprint-proxy, being the lateral extent of the 70% flux footprint, was used to determine how far from the measurement tower the flux readings originated from. From this data, only the fluxes with a footprint length of 300 metres or less were used due to the extent of the clear cut. Eight means were then computed for each year, which were compared to each other and between the two years. An increasing trend in NEP was observed in the first half of 2022, and a significant decrease in NEP, i.e. an increased uptake of CO2, was found between the years 2022 and 2023. This confirmed the initial hypotheses and agreed with previous research. It was furthermore observed that a remarkable spatial variation in flux means was present in 2022, where the most productive quadrant was observed to be the East-facing. Aside from this, the spread of the data across all sectors in 2022 was much wider than in 2023, further underlining the conclusion that the clear-cutting did have a significant impact on the forest’s NEP. Future studies could now have the goal to investigate what could be causing this spatial difference in flux means in order to possibly define guidelines as to how a forest can be managed more sustainably from a CO2 flux perspective. Another future study would keep looking into the evolution of the forest’s NEP over the next decades to gain insight in how well this clear-cut forest regains its property as a carbon sink.