Determining the humus formation index of forest soils of the Vologda Region Yliya Duryagina, Ludmila Voropay, Svetlana Hamitova, Ilfir Galiullin and Olga Kuztetsova BIO Web Conf., 37 (2021) 00062 Published online: 27 October 2021 DOI: 10.1051/bioconf/20213700062