Investigation of plant production potential on sand dune systems of Iran using water balance model

Sand dunes as a feather of desert regions are very important from different aspects. Considerable area of Iran's sand dunes (about 4.5 million hectares) are sensitive to wind erosion. There have been many sandstorms in the study areas that have caused huge losses of arable soil and threatened the vegetated area and living environment of local people. Water is the most important restrictive factor for vegetation growth in arid and desert areas particularly in sand dune systems. For development and establish of vegetation cover such as rangeland, forest and agronomy, it is necessary to investigate and monitor the fate of water and water balance on sand dunes. A conceptual water balance model for the dune system of Khuzestan, Kashan and Khorasan (Dolat- Abad sand dunes) was considered based on the principles of hydrologic cycles of water in soil. Inputs include rainfall, any flow from groundwater capillary rise or water vapor due to condensation process and watering such as irrigation. Outputs are the losses of water out of the sand profile by percolation to water table by, evaporation from sand surface areas, evapotranspiration from grasses, bushes and trees. Storage change is the difference in the amount of water in the dune system. This water can be held in the dunes as water holding capacity of the dune sand and, in the soil moisture zone where plant roots extract water. Changes in storage in the saturated sand are visible as changes in the water table level. Moisture content of the sand dune for the selected sites both for bare and vegated dune were measured monthly using TDR device or by taking sand samples and gravimetric method. Meteorological data such as daily precipitation, temperature, potential evaporation from adjacent meteorological station were collected and evaluated with weekly or monthly recorded moisture content using general water balance equation. Results showed that Dovlat-Abad bare sand dunes could be classified as semi infiltrative sand dunes group in which, deep percolation is negative for summer and autumn periods, therefore rainfall can not recharge water table but in winter time the water balance for percolation is positive and rainfall can replenish underground water. It is concluded that in a natural condition of desert ecosystem it appears that in the investigated are natural rainfall is sufficient to establish xerophytes shrub and trees such as Haloxylon and other native shrubs. It seems that, precipitation is the only major source water requirement of dune plants in Khorasan and Kashan except in Khuzestan sand dune that the role of water table both directly or in the form of vapor condensation is important.