Phenology study of Astragalus chaborasicus، Poa sinaica وStipa hohenackeriana calculated by Growing Degree Days (GDD) in Khoshkrood saveh Region

Information on phenology of the range species is important to manage the plans of plant utilization, control of the livestock entry and exit, seed collection, and understanding of the nutritive value of plant species in different phenology stages. In this study, phenology of three important rangeland species namely Astragalus chaborasicus, Poa sinaica and Stipa hohenackeriana was studied in Khoshkehrood saveh region. Vegetative and reproductive data of the mentioned species were recorded once a week for two years (2007 and 2008). Growing Degree Days (GDD) were determined using climate data (temperature and precipitation) collected from the nearest station to Saveh. The results showed that start and end of the phonological stages differed in two different years while GDD was almost same for phonological stages. In other words, phenological stages have constant temperature requirement which after obtaining the required temperature the emergence of the stages are observed and thus GDD is applied for prediction of phenological stages.