investigation of vegetation changes under precipitation in semi-steppic rangelands of ardebil province (case study: arshagh rangeland research site)

a major part of the rangelands of iran are located in arid and semi-arid regions. in this climate, rainfall fluctuation is an important factor which affects vegetation and forage production. in dry years that rainfall decreases, surface vegetation and forage production is damaged. this study was conducted on semi-steppic rangelands of ardebil over nine years (1999-2007), to study of vegetation changes with rainfall fluctuation. the results showed that canopy cover of salsola gemmascens and noaea mucronata species was decreased but artemisia fragrans and kochia prostrata species were increased.generally density of shrub species was decreased about 40% and showed a positive correlation with seasonal precipitation (fall and winter). grass species showed different response to precipitation changes over nine years period and in general, no significant changes were observed. stipa hohenackeriana species was affected by winter precipitation but poa bulbosa and cynodon dactylon were correlated with spring precipitation. density of perennial forbs species was increased considerably (about seven times), but in dry years (2000-2002) forage production reduced.  forage production over nine years increased from  296 kg to 747 kg per hectare, which is approximately 2.5 times higher. meanwhile, proportion of plants in classes i, ii and iii, were respectively, 23.1, 51.9 and 25.2 percent of forage production. also, forage production in wet periods increased from 747 to 1968 kg per hectare which shows an increase of about seven times.