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Fig. 13.4 Interrelation of typical fodder ( Artemisia diffusa ) and unpalatable species ( Peganum
harmala ) along a grazing gradient from a fixed watering point in Karnabchul
(Gaevskaya 1971 ;Salmanov 1986 ). This type of rangelands is characterized by
low forage productivity (0.15-0.36 t DM/ha 1 ) with high interannual variations
that is largely dependent on climatic conditions (Gaevskaya and Salmanov 1975 ).
The vegetation of Artemisia -ephemeral rangelands is the main source of forage for
livestock, and has been throughout history. Despite the low forage production of
these rangelands, they provide 95 % of total diet of livestock. Anthropogenic impact
is thus a part of the disturbance regime to which this area has been exposed since
time immemorial.
Throughout the 40 years since the well was established, A . diffusa has been
constantly overgrazed and trampled by livestock. Vegetation is usually absent
around the well within the radius of 60-80 m. This zone is characterized by a highly
compacted, flat surface with black or brown color as a result of intense trampling.
At the next 1,000 m from the well invader plant P . harmala dominates. This plant
is recognized as an indicator of overexploited-overgrazed rangelands and is not
touched by livestock because of its toxicity, strong characteristic smell and high
content of alkaloid in green leaves and seeds (Gintzburger et al. 2003 ). P . harmala
thus dominates the first 1,000 m from the well (Fig. 13.4 ). A rise in the number of
unpalatable plants in vegetation composition results in decreased qualitative values
of the rangelands. Presence of P . harmala can be used as a sign of beginning of
severe changes in vegetation structure under the intense grazing.
The shift towards dominance of unpalatable plants in vegetation composition
has resulted in very low quality of grazing rangelands in term of fodder value of
plants. As a function of increased distance away from the watering point, available
grazing area for animals increases and stocking pressure on the this area decreases
(Andrew and Lange 1986 ). This is reflected in the appearance of A . diffusa in the
area of 2,000 m from the well (Fig. 13.4 ). Relatively high grazing pressure promotes
P. harmala to remain in the vegetation cover consisting of 31 % of total vegetative
cover and 18 % of the density in plant composition. In contrast, 56 % of the total
perennial biomass of vegetation community in the distance of 2,000 m consists of
P . harmala . Beyond 2,000 m, A . diffusa becomes more abundant and at a distance
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