Uzbekistan: Rehabilitation of Desert Rangelands Affected by Salinity, to Improve Food Security, Combat Desertification and Maintain the Natural Resource Base - Combating Desertification in Asia, Africa and the Middle East - page 247

last states of vegetation succession, some dominant ephemerals disappeared from
the vegetation community because of high trampling by livestock animals, but not
because of overgrazing. Besides trampling and grazing pressure, another important
factor of vegetation change is over-supply of natural fertilizers and moisture (e.g.
animal dung and urine) in topsoil around water wells due to high animal density and
intensive utilization of water points. This, apparently, transforms soils around water
sources into more mineralized conditions and consequently affects underground
micro-flora and aboveground vegetation.
Increased grazing-driven disturbance has resulted in replacement of ephemeroids
by undesired annuals. The radial symmetry of grazing pressure around the well
has resulted in more rapid changes in vegetation structure than around the village
where the grazing intensity is distributed around the elongated village area. Different
edaphic factors played a key role in the formation of vegetation structure. Such
vegetation changes of rangelands under the impact of grazing are distinctively
described by integration of the S&T model. Piosphere analyses helped to identify
states and transitions of vegetation communities and their shifts over time under
grazing-induced disturbances. Application of such ecological concepts in range
assessment helps to understand the driving factors of vegetation changes and
to provide a framework for solution of degradation problems and sustainable
management of natural resources.

3.2 Vegetation Changes Along a Salinity Gradient

Dryland salinity and associated water quality are recognized to be among most
severe natural resource degradation problems in the marginal desert belt of Aral
Sea Basin. The annual losses in Uzbekistan due to salinization have been estimated
at US$ 31 million, while withdrawal of highly salt affected lands out of agricultural
production costs an estimated US$ 12 million annually. Most of the irrigated lands
in Aral Sea Basin are subjected to salinity due to sharp continental arid climate with
aridity coefficient from 0.12 to 0.3. Initial sources of the accumulated salts in soil
profiles are irrigation water. The risk of salinization is further increased due to the
rising water table associated with poorly managed drainage systems.
Salt affected lands in desert areas of Uzbekistan demonstrate the most charac-
teristic features of natural continental (not marine/coastal) salinization and alka-
linization. Low organic matter ( 1.0 %) and high accumulation of salts and poor

water holding capacity render these soils unproductive. The predominant salinity
type is sulfate-chloride. Sodium and magnesium are the dominating cations. Total
nitrogen (N 2 ) and phosphorus (P) contents usually ranged between 0.7-5.5 and
10.0-18.26 mg/kg, respectively. Available potassium (K C ) content is classified as
low or moderate. The dominant cation is Na C and the dominant anion is SO 4 2 .
Focusing on countrywide soil chemistry of surveyed salt -affected areas with
shallow water table we found out that the predominant salinity type is chloride-
sulphate, while sulfate -chloride type is also described. Ground water salinity

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