Abstract <p>The litter–bag technique was applied to study decomposition processes of plant residues in urban forest biogeocenoses in the Arboretum of Moscow State University Botanical Garden. The study was performed in various zonal biogeocenoses starting with the zone of mixed forest (Moscow oblast) to dry steppes (Volgograd oblast) in order to determine the leading factors of decomposition of the test materials. Standardized samples of wood, cellulose, tea, and native forest litters were placed on the soil surface (into or under the forest floor) and then sampled at different time intervals. The dynamics of mass loss was estimated for each test plot, and some zonal and local decomposition patterns related to the decomposition factors were described. It was shown that the leading decomposition factors were particular for different materials. The decomposition of wood and cellulose was mainly controlled by temperature and moisture. The tea decomposition rate at the initial stages depended on temperature and moisture, but differed in deciduous and coniferous forests. The decomposition rate of native litters was not controlled by climate in the studied zones. Wood decomposition in the Botanical Garden of Moscow State University was slowed down to the rates typical for zonal forests located 320–440&#xa0;km to the south. The native litters in coniferous forests of Botanical Garden, on the contrary, were decomposed faster than in natural biogeocenoses, which corresponded to previous data on litterfall input and litter reserves. The specificity of the use of some test materials to study decomposition factors and processes in human-affected biogeocenoses, of wood as a test material in particular, is shown.</p>