<p>Within Yekaterinburg (Middle Urals, Russia), remnants of old-growth pine forests of natural origin have been preserved. Traditional urban management practices—landscape redevelopment, tree felling and planting, grass cutting, mechanical soil disturbance, and forest litter removal—are not applied in these forests. The case of Yekaterinburg provides a unique opportunity to study the impact of other agents of urbanization—chemical and thermal pollution, the naturalization of adventive flora, and recreational loads—in their “pure” form. We analyzed humus forms, types of the morphological structure of topsoils, whose diversity within a given area is determined by the composition and abundance of decomposers, primarily macro- and mesofauna. Humus forms in urban forests within the city were compared with their suburban counterparts. The identification of humus forms was based on the European morpho-functional classification of humus systems and forms. The direction of changes in humus forms depends on the balance of various urbanization factors at different scales. These factors include city-wide influences (thermal pollution, eutrophication from atmospheric deposition and other sources, invasion of deciduous trees and shrubs into coniferous forests) and local factors (trampling due to recreational activities). Under low recreational loads, the spectrum of humus forms shifts towards more zoogenic variants, with Oligomull and Mesomull replacing Dysmull. In contrast, high recreational pressure shifts the spectrum towards less active humus forms, where Hemimoder, Eumoder, Hemimor, Humimor, and Eumor replace Dysmull. These transformation pathways can have opposite effects on the carbon cycle under urbanization conditions: in the first case, carbon is primarily accumulated in the organic-mineral horizons, while in the second case, it is deposited in the forest litter.</p>