The article gives a brief analysis of the concept of the forest biogeocoenotic cover mosaic. The elementary unit for investigation of soil-plant relationships – elementary biogeorange (EBGR), is suggested and substantiated. Numerous examples from boreal forests show that EBGR is an elementary provider of ecosystem functions such as soil fertility formation and biogeochemical cycle regulation. The example of soil fertility formation is used to demonstrate that the informative parameters for soil-plant relationships at the EBGR level are the soil dynamic properties (soil acidity, nitrogen, nutrient compounds available to the biota, etc.).