Importance value changes in various plant life forms during growing season (Case study: Nodushan Steppe Rangelands Yazd Province)

Change detection in plant production, canopy cover and importance value of dominant plant life forms during growing season can assist range managers to select appropriate management practices. This research carried out during 2008-2009 in Nodushan rangelands in Yazd province. Random sampling with one m2 plots was used to determine importance values of available plant life forms including grasses, shrubs and forbs. The measurements were conducted in early, mid and late stages of growing season. According to the results, shrubs had higher importance value than grasses and forbs during the growing season. The importance value of shrubs was increased during growing season but this index was decreased for grasses and forbs. Canopy cover and forage yield of all studied plant life forms had significant correlation during growing season (P<0.05) and R square value were 0.84, 0.78 and 0.67 for forbs, shrubs and grasses respectively. Therefore in spite of minor changes of importance value during growing season, significant relationships between plant cover and production justifies the estimation of range production from vegetation cover data.