عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Studying the phenology of range species is an important factor in management actions for optimal utilization of these species. On the other hand, drought and stresses arising from it cause to the changes in plant growth stages, affecting forage yield. Bromus kopetdaghensis ، Festuca arundinacea ، Stipa arabica and Poa bulbosa are the main elements of semi-steppe areas to dry forests of Khorasan rangelands as relatively palatable species, grazed by livestock. In the current research, phenology of the mentioned species was studied during 2007-2010. Moisture conditions and drought classes were also studied by Standardize Precipitation Index (SPI) in rangelands of Binalood, Khorasan Razavi province in a twenty-year period. Effects of different drought periods were investigated on emergence of plant organs and the period length of vegetative and reproductive stages. Results showed that reproductive growth was shorter during drought period. Under drought conditions of 2008, vegetative growth was started earlier compared to other years and the change from vegetative to reproductive stage occurred in a shorter period. Results of growth degree-day showed that the range was from 2814.12 in 2010 to 2406.95 centigrade degree in 2008. Consequently, GDD model could be used with relatively high accuracy in determining the appropriate time for livestock entry and exit.