Biological Activity of Mountain Soils of the Western Caucasus after Deforestation

A study of a set of indicators characterizing the ecological state of forest soils in the mountains of the North-Western Caucasus under broad-leaved and mixed forests has been conducted. The aim of the study has been to assess changes in the biological activity of soils of different genesis after deforestation. The objects of the study have been rendzina, gray forest and gray forest-steppe soils of forest and disturbed ecosystems of the Republic of Adugeya at altitudes from 500 to 1635 m above sea level. Logging plots of different ages (from 10 to 40 years old) after deforestation have been considered. The analyzed indicators have included: the content of total and active carbon, the activity of soil enzymes (catalase, invertase, dehydrogenase, urease, phosphatase), the number of bacteria, as well as an integral index of the biological properties of the soil. The correlation of these indicators with hydrothermal conditions, density of soil structure, penetration resistance, medium reaction, hydrolytic acidity, total absorbed bases and other soil parameters has been evaluated. The level of biological activity of soils in logging areas in the low mountains of Adygea depends on the relief and the timing of restoration after deforestation. Even after several decades of restoration of woody vegetation on the slopes of 12–15° there is no complete return of biological activity to the values of Greyic Phaeozem Eutric of the background forest area. 40 years after logging, the integral index of biological properties of gray forest soil is still 17 % lower than in the control plot. The biological activity of post-forest soils can change in three main directions. On steep slopes, with severe disturbance of the soil and vegetation cover due to the operation of heavy machinery, the integral index of the biological properties of soils decreases by 25–40 % or more without a tendency to recovery. At an average level of disturbance in plots with slight slopes, after an initial decrease, the soils are restored to control values. Restorative successions with intensive development of herbaceous flora and the turf process with slight disturbance can lead to an increase in biological activity above the control values in just 2–3 years. Comprehensive biodiognostic studies using an integral index of the biological state of the soil have revealed, in general, increased stability of low-mountain terrain soils (gray forest and forest-steppe) compared to the soils of the middle mountains of Adygea (rendzina soils). The main degradation factor that reduces the biological activity of soils disturbed by logging is erosion.