Abstracts

Soil Ecosystems

Grassland resources are important on a world-wide basis. Intensified grazing is one of the main causes of ecological change of meadows and steppes. Almost all steppes are grazed and represent different stages of succession. Heavy grazing impact generally initiates a retrogressive succession (degradation) including a decrease in above-ground net primary production and phytomass as well as a change in species composition, especially in dominant structure. Removal of grazing pressure leads to a progressive succession (restoration) with an increase in phytomass and production and replacement of degraded pasture community by the original plant association. Stocking rate is one of the most important factors affected a steppe ecosystem dynamics.

In this paper we focus on the influence of grazing impact on phytomass stores in Inner Asia dry steppes including steppes of Tuva and Trans-Baical (Russia) and Mongolia. The following variables of the plant biomass structure are used: Gmax – maximal standing crop of green phytomass, D – standing dead phytomass, L – litter, B – living below-ground organs, V – dead below-ground phytomass (Table 1).

Table 1
Above and below-ground standing crops in dry steppes. Mean annual g/m2 dw, 0-20 cm soil layer. LG – lightly grazed, MG – moderately grazed, OG – overgrazed

Maximal standing crop of green phytomass, standing crop of above dead phytomass (D+L) and living below-ground organs (B) decrease with the increase of grazing pressure. The pattern of dead and total below-ground phytomass change is different. The standing crop of V in Tuva varies about 1200 gm-2 and is not influenced by grazing, whereas in Trans-Baical steppes the stores of V decrease under the grazing impact. It is clear that grazing results in a decrease of living phytomass standing crop (Gmax+B) and may cause a dynamics of plant biomass structure in different steppes.

Note. Abstracts are published in author's edition

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