Abstract: Based on Ulmus pumila phenophase and simultaneous extreme temperatures data in Wuchuan and Ongniud area of inner Mongolia during 1985-2012,the change characteristics of Ulmus pumila phenophase and its response to extreme temperatures were investigated using linear tendency estimation and Pearson correlation coefficient methods.The study will play an important role in guiding forest productive practice.The results show that the extreme maximum temperature fluctuates inconspicuously in the two studied areas during 1985-2012.On the contrary,the extreme minimum temperature indicates a dramatic and different variation in the two areas.The extreme minimum temperature in Wuchuan increases with a tendency rate of 0.617℃/10 a and that in Ongniud decreases significantly with a tendency rate of -0.678℃/10 a,respectively.In addition,the Ulmus pumila florescences in the two areas show a starting earlier trend,but the end dates of leaf fall lag behind and bring forward significantly as well as the growth periods prolong relatively with a rate of 14.14 d/10 a and 2.37 d/10 a in Wuchuan and Ongniud,respectively,throughout the recent 28 years.In conclusion,the extreme maximum temperature is the key meteorological factor impacting the Ulmus pumila florescence while the end date of leaf fall of Ulmus pumila is more sensitive to the extreme minimum temperature.

Key words: Ulmus pumila, Phenophase, Extreme temperature, Climate tendency rate, Correlation analysis