Applying thermal index to predict the phonological stages of Thymus growth in natural habitats

Given the variation in climate conditions in a region, predicting the phenological stages of growth based on time calendar is not sufficiently accurate. In this regard, the use of thermal index can provide a more accurate estimate for the phenological stages of the plant growth. In order to study the phenological stages of various Thymus species, a research was implemented in the natural habitats of west Azerbaijan, Isfahan, Tehran, North Khorasan and Qazvin. First of all, the habitats of each study species were determined. Then, using the data obtained from the nearest meteorology station, the climate condition was specified for each habitat. After determining the study sites, the factors including altitude from sea level, geological situation, slope percentage and direction, and other features of the area were specified. In each site, plant and soil sampling was performed in a randomized systematic method using 25 square meter plots. In addition, for each Thymus species in each habitat, phenological data were recorded based on time calendar and thermal index (growth degree day, GDD). According to the results, Th. pubescens, in HAJI BEYK region of west Azerbaijan and DEHDAR region of Alborz province, reached the flowering stage at 770 and 775 GDD, and reached the seeding stage at 1923 and 1810 GDD, respectively. Thymus kotschyanus, in GHOOSHCHI region of west Azerbaijan, DEHDAR TALEGHAN of Alborz province and QOSTINLAR of Qazvin province, reached the flowering stage at 770.5, 762 and 750 GDD, and reached the seeding stage at 1680, 1541 and 1512 GDD, respectively. Thymus daenensis, in ESKANDARI region of Isfahan province and ABEGARM region of Qazvin province, reached the flowering stage at 662 and 629 GDD, and reached the seeding stage at 1404 and 1465 GDD, respectively. Thymus carmanicus, in KHANSAR region of Isfahan province, reached the flowering stage at 848 GDD, and reached the seeding stage at 1354 GDD. Thymus transcaspicus, in ASADLI region of north Khorasan, reached the flowering stage at 772 GDD, and reached the seeding stage at 1172 GDD. Using the thermal index, the exact time to collect the plant organs like flowers and seeds could be predicted based on prediction and decision models. Even, determining the time of reaching each phenological stage could be possible in controlled agricultural systems with high precision.