Assessment of Within-Forest Variability in Albeluvisol Quality in an Urban Forest Ecosystem for the Northern Part of the Moscow Megalopolis

Abstract

Extremely high variability of urban soils is a serious problem for their environmental quality assessment, monitoring and prediction. The principal factors of their spatial variability include mesorelief. The effect of mesorelief on soil spatial patterns in underestimated so far, but necessary for environmental monitoring and environmental impact assessment purposes. Choosing a relevant reference (background) site is crucial for environmental monitoring, assessment and prediction. In a huge and heterogeneous territory of Moscow megalopolis the number and variety of reference sites shall correspond to the variability of environmental conditions. The central core of the Forest Experimental Station (FES) of the Russian State Agrarian University – Moscow Timiryazev Agricultural Academy (RSAU-MTAA) is a relevant reference site for the northern part of Moscow. The area includes forest ecosystems representative for the south taiga zone and historically dominated this territory. FES is the biggest urban forest of the Timiryazev municipal district, which is one of the least disturbed and the most environmentally friendly part of Moscow. The FES has well conserved natural vegetation dominated by pine communities (34% forested area) with participation of linden, oak, elm and maple in the better drained parts of the slopes. The average age of the stand is about 100 years. FES’ vegetation and soils are comparable with vegetation and soils in the Central Forest Preserve which is the principal reference site of the regional monitoring in southern taiga zone of the European part of Russia. These two areas have similar soil cover patterns and landscape organization, dominant soil profiles, their texture, lithological construction, soil feature and regimes, and even actual soil forming processes and successions. Typical for zonal forest ecosystems, the FES autonomous landscapes have soft mesorelief forms with 175 m maximum and 160 m minimum absolute heights above sea level and soil quaternary parent materials represented by low-power silty cover loams (up to 0.5 m), underlain by clay-loam moraine or sandy fluvio-glacial sediments. Their combinations particularly increase the within-forest variability of topsoil texture, hydro-physical and chemical features of the zonal Albeluvisols with soil cover patterns generally determined by the mesorelief slope forms. Albeluvisols in the summit and slopes have essential differences in the depth (almost in 2 times), propertied of humus-accumulative topsoil and principal subsoil horizons including the topsoil average moisture (up to 13% per season), temperature (up to 4.6 °C), Corg content (up to 1.5% in AY horizon), CO₂ fluxes (more than 2 times per season and 26.2 g m⁻² d⁻¹ in May) and heavy metal behavior (up to 5.8 g m⁻²Pb in topsoil, 4.9 mg m⁻²Pb in the yearly-spring snow cover, 10.5 mg m⁻²Pb in the background grassy vegetation cover). Mesorelief increases the spatial variability of soils at the reference sites and therefore may affect the environmental quality assessments of the urban soils which are compared to this reference. Mesorelief shall be considered for the man-changed soil quality assessment in the processes of landscape design, local environmental monitoring or impact assessment (EIA).