Regularities of spruce-fi r and oak forests distribution over the Udyl’ State Nature Reserve (the lower Amur River region)

The identification of relationships between forest spatial distribution and relief features is among the main objectives in studying the structural and functional organization of forest ecosystems. The revealed patterns of forest distribution make it possible to predict their response to external environmental changes. In the Lower Amur River region, such studies are quite insufficient. The study objective is to identify relationships between spruce-fir and oak forests’ distribution and relief parameters in the region. For this purpose nine sampling plots were placed and described in 2014–2017 in spruce-fir and oak forests of the Udyl’ State Nature Reserve located in the Lower Amur River region. The relief matrix was obtained from the digital model of the NASA SRTM3 project, and morphometric values of relief parameters were calculated for each sample plot. It was found that there is a thermal inversion in soils of the region under study coming from the occurrence of permafrost in depressions and its absence on mountain slopes. As a result the altitudinal distribution of forests is disrupted – the oak forests grow higher on the slopes than the spruce-fir ones, thus producing the inversion of forest types. Spruce forests more often occupy the northern and eastern gentle slopes, while the oak forests grow on the southern and western steep slopes. Light intensity in the spruce-fir forests ranges from 20 to 22 %, being from 34 to 37 % in the oak forests. Light intensity in the oak forests increases with increasing azimuth and reaches the maximum when the Sun is in the southwest. Spruce-fir forests occupy negative topographic forms, growing in the zones of weak accumulation. Oak forests often occupy positive topographic forms, such as medium-convex and crest ones, located in the denudation zones of water and lithodynamic flows. Slopes with spruce-fir forests have larger catchment areas of liquid and solid substances, higher flow intensity index and topographic humidity in comparison with the oak forests.