Dataset of understory reflectance spectra and fractional cover in a boreal forest area in Finland

The dataset includes forest floor spectral reflectance factors at wavelengths of 350–2500 nm, fractional cover data of forest floor, forest inventory data, and data on the light availability at forest floor (diffuse non-interceptance, DIFN) and tree canopy structure (effective plant area index, PAIe). The data were collected near peak growing seasons 2018–2019 in situ in total of 36 forest stands in Hyytiälä, Finland (61°50’N, 24°17’E). Each study stand represents a forest site (fertility) type: OMT (herb-rich), MT (mesic), VT (sub-xeric), or CT (xeric), based on Cajander’s theory of forest types [1]. The first spread sheet contains descriptions of the variables, second spread sheet the stand characteristics, and third the spectral data. Version history: This is Version 3 of the dataset, which was used, together with data from [6], in the study of Forsström et al. [2]. If using Version 3, please cite Forsström et al. [2, 3]. Version 2 had an indexing error that caused the spectral data to be in the wrong order. Do not use Version 2. Version 1 was used in Forsström et al. [4]. It did not include canopy structure data and applied slightly different preprocessing of the spectra. If using Version 1, please cite Forsström et al. [4, 5]. We thank Lauri Korhonen, Ville Ranta, and Daniel Schraik for collaboration. Data collection and preparation was supported by the Academy of Finland [BOREALITY, grant number 286390; and DIMEBO, grant number 3323004]; and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme [grant agreement No 771049]. The article reflects only the authors’ view and the Agency is not responsible for any use that may be made of the information it contains. [1] Cajander, A.K., 1926. The theory of forest types. Acta Forestalia Fennica. doi:10.14214/aff.7193 [2] Forsström, P.R., Hovi, A., Juola, J., Rautiainen, M., 2023. Links between light availability and spectral properties of forest floor in European forests. Agricultural and Forest Meteorology. doi:10.1016/j.agrformet.2023.109481 [3] Forsström, P.R., Juola, J., Hovi, A., Rautiainen, M., 2024. Dataset of understory reflectance spectra and fractional cover in a boreal forest area in Finland. Mendeley Data, V3. doi:10.17632/2g9nkcdj53.3 [4] Forsström, P.R., Juola, J., Rautiainen, M., 2021. Relationships between understory spectra and fractional cover in northern European boreal forests. Agricultural and Forest Meteorology. doi:10.1016/j.agr