Document Type : Research Paper
Authors
Abstract
Study of vegetation changes of ungrazed rangelands is important. It is supposed that ungrazed areas tends toward climax and range condition to be improved. The major portion of our rangelands are laied in arid and semi-arid regions. For that precipitation is the major influential factor on vegetation changes. In dry years as rainfall decreases, the vegetation cover are damage. This study were conducted on Rudshur rangelands for nine years (1996-2004), with the aim of rainfall variation and ungrazed condition effects on vegetation changes. Plant parameters as canopy cover, density and seedling numbers were estimated on permanent plots each year. A dry period were started in 1997 in the region and continued for five years. Results showed, in a period of nine years, total canopy cover declined 40 percent. Decline of canopy cover varied from 26 to 95 percent for different species. Only canopy cover of the Poa sinaica increased about three times, due to earliest vegetative period in growing season. Decline in canopy cover was greatest in forbs, and grasses had lower decline. Regeneration was high in the rainy years and 81 percent of total seedlings belonged to grasses especially to Stipa hohenackeriana. Density of most species decreased in the study period especially in dry years.
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