A set of field and laboratory methods that provides an assessment of the biological diversity and ecological functions of xylotrophic fungi in forest ecosystems is considered. They can be used to assess the biodiversity of this fungi group, its role in the biological cycle of forest ecosystems in Northern Eurasia, and to assess the transformation of fungal communities under the influence of climatic and anthropogenic factors. Methods for estimating the intensity of mineralization of wood residues can be used for ground-based monitoring of remote sensing data in the context of monitoring CO2 fluxes between forest cover and the atmosphere. Methods for assessing the wood-destroying activity of xylotrophic fungi, the external manifestation of which is the СО2-emission activity of wood debris, can be used to study the response of the emission constituent of the carbon cycle of forest ecosystems to climatic changes.