Comparative assessment of impact of the pyrogenic factor on the vegetable cover of the steppe zone

Reducing in grazing pressure leads to gradual increasing of biomass and is a basic resource af-fecting pyrogenic factor. In the conditions of mead-ow steppes fire is more or less pernicious for her-baceous vegetation. In this case the fire burns litter, herbs with shallow root system, low growing trees and shrubs, destroys herbs with superficial root system, trees and bushes with low crown, leads to change of a ratio of different groups of plants, weakens the role of bushes and large herbs. For studying of features of restoration of vegetation af-ter action of the pyrogenic factor which occurred by the end of vegetation of 2012 the accounting of re-construction of the reravine (after the fire) and natu-ral herbage of the meadow steppe was carried out, on sites of a high terrace of the suburb of the city of Yakutsk with the frozen -inundated layered soils which are characterized by existence of cryogenic and post-cryogenic texture. Weather conditions of. Yakutsk are characterized by sharply continental and short, rather hot and droughty summer. The vegetative period is 155 days, a precipitation to-taled 162 mm. Weather conditions of the studied year favored the increase of dry biomass of the meadow steppe grass stand before the fire oc-curred. Taproot species, such as flax (Linum perenne L.) and gray speed well (Veronica incana L.) were damaged by fire since their dormant buds are situated above the ground. Re-newal of bichromatic euphorbia (Euphorbia discol-or), a Siberian cock's head (Onobrychis sibirica), restoration of these types on the experimental plot happened due to the amount of seeds in the soil. Total underground reserve (R) in the studied root mass made up 58.9 g/sq.m. at the depth of 0-30 cm. The portion of meadow transbaikal grass (Poa transbaicalica Roshev.) in the above-ground mass was 63 %. The portion of litter (0.4t/hectare) in the above-ground mass (1.6 t/hectare) did not exceed 30%. Underground productivity of steppe communi-ties after the fire was 9.4 t/hectare in autumn which is 2.8 times less than that of intact communities. Thus, the influence of pyrogenic factor caused the change of vegetation structure due to intensive re-newal of cereals, leguminous crops and losses of some types of meadow grass, and also influenced the reduction of underground efficiency of vegeta-ble substance.