This dataset contains description of thinning, and forest and carbon stock inventory results of the forest stand surrounding SMEAR II research station located in Hyytiälä, Finland. The dataset consists of following files: 1. Description of thinning and inventory methods (Hyytiala site description.pdf) 2. Forest characteristics before and after the thinning, by measurement plot (Forest characteristics.xlsx) 3. Carbon stocks before and after the thinning, as well as carbon stocks in commercial removal, by measurement plot (Carbon stocks.xlsx) 4. Equations used for procuding estimates presented in products 2&3 (Equations.xlsx) 5. Readme-file explaining details regarding variants in products 2&3 (Readme.xlsx) 6. Plot map showing the locations of measurement plots (Plot map.xlsx) 7. Tree size distribution before and after the thinning (Tree size distribution.xlsx) 8. Cleaned tree-wise inventory data (Plot measurement data 2020.xlsx) from 2019 understorey measurement results 2020 measurement results Plot 1-24 detailed inventory measurement results