Study the Growth degree days requirement for phenological stages of important Range species in Homand

The phenological stages of five species Festuca ovina, Koeleria macrantha, Koeleria phleoides, Melica cupani and Melica jacquemntii were studied for three years(2003-2005) in Homand-e-abesard rangeland research station, in 70 km east of Tehran. Annual life cycle of plants were divided into two large periods, more active and less active phases. data were recorded in the first phase every 7 days and in the second phase every 15 days. The Growth degree-days(GDD) were calculated for each phenological stages. 20 stands of each species were studied. The phenological stages include: growth initiation(gi), vegetative growth(vg), heading out(ho), full flowering(ff), seed ripening(sr), seed maturity(sm), temporary dormancy(td) and regrowth. The result showed that the five species started their growth from early March and dried in late July. There was dormancy for late August to early October and a regrowth stage from late November to late December. The Growth degree days were calculated for each phenological stage of 5 species in the different years. The result showed no GDD variation for the same phenological stages between years.