The main problems of ecology and fertility of soils in the aspect peculiarities of the nature of the mountain brown–carbonate soils of the Western Tien Shan. An analysis of own and available in the literature data of comprehensive studies that allow to determine the causes of erosion and loss of soil fertility, depending on the relief and exposure of the slope. The results of an assessment of the humus state of eroded soils formed in mountain conditions are considered. The article deals with the humus condition of the main types of soils of vertical belts. In general, our studies show that these ratios of Сga:Сfa correlate with soil susceptibility to erosion processes, depend on slope exposure and slope elements. The expansion of Сga:Сfa is accompanied by an increase in the optical density of humic acids. Differences in resistance to coagulation between humates of different soils, to varying degrees of susceptibility to erosion and anthropogenic factors, correspond to differences between them according to their optical properties.