Most of fungal species inhabit forest areas, where they perform many important ecological functions that contribute significantly to the stability of entire ecosystems. The importance and extent of the influence of numerous environmental factors on the richness, composition, and functional diversity of fungal communities are poorly understood. In Croatia, the biodiversity of fungi in the Mediterranean region is the least studied and is therefore investigated by this project. The main objective is to determine the influence of environmental factors (soil chemical properties and microclimatic parameters - temperature, humidity) on spatial and temporal changes in biomass, diversity, and functional composition of soil and litter fungal communities in forest habitats of the Mediterranean region of Croatia. The research method used for the identification of fungal taxa in the project is DNA metabarcoding of environmental samples (eDNA) based on high-throughput sequencing technology. The project results will fill the gap in our knowledge of the fungal biogeography of forest ecosystems in Croatia and in southern Europe as a whole, and will provide a better overview of the environmental factors shaping fungal distribution patterns on a global scale. Knowledge of fungal biodiversity and the environmental factors that influence its distribution is one of the prerequisites for appropriate assessment, sustainable use and conservation of highly valuable forest resources for future generations.