This paper presents the results of studying the ash content of twig and leaf debris from forest plants of primary midmountain tropical forests of Central Vietnam (Bidoup Núi Bà National Park) in order to identify and clarify the elements that enter the soil during their decomposition. The difference in the ratio of twig and leaf debris in mortmass samples collected in different landscape conditions is shown. At the same time, the influence of periodical and stagnant moisture conditions on the conduct of migratory soil processes is considered. The sampling points of the twig and leaf debris correspond to the locations of the soil catena within the structural ridge and its top, slope, and foothill. This allows us to relate the results obtained on the elemental composition of the twig and leaf debris to the geochemical migration of chemical elements in different geochemical landscape conditions, from automorphic to accumulative. An attempt has been made to establish the volumes of matter migrating from the mortmass into the soil together with the aqueous solution. Differences in the accumulation of ash elements in the twig and leaf debris depending on the position in different landscape conditions are revealed. The composition of elements entering the soil with twig and leaf debris and involved in geochemical migration is established, and the contribution of leaves and twig debris to the accumulation and migration of elements under different moisture conditions is evaluated. The dependence of geochemical migration processes on the position of the elementary geochemical landscape facies in the catena is pointed out, which manifests itself in a change not only in the total ash content of the twig and leaf debris, but also in the ratio of ash content of twig debris to that of leaf debris.

Expeditionary studies of the functioning of landscapes of mid-mountain monsoon (including fog) forests have been being conducted within the landscape and ecological station in the territory of the Bidoup-Nui Ba National Park and the adjacent Hon Giao since 2018 and are currently underway. One of the research objectives is to clarify the biogeochemical migrations of the material composition of soils in the “leaf debris–soil” system. We have consistently studied natural objects for their material composition as well as the intensity and rate of involvement of chemical elements in physicochemical migration processes in the “leaf debris–soil” system. Our findings indicate an active influx of a select group of examined elements (Se, Pd, Ag, Cd, Sn, Bi), particularly Bi, Pd, Se, and Cd, through the leaf debris and the detachment of aboveground plant organs, warranting their integration into organogenic soil horizons. Subsequently, lateral migration (Pd, Cd, Se) ensues. Slope processes within subordinate landscape facets, in addition to soil moisture and aeration processes, contribute to the subsequent redistribution of elemental volumes introduced into organogenic soil horizons.