Effect of air temperature on forecasting the start of Cupressaceae pollen type in Ponferrada [Leon, Spain]

In order to survive periods of adverse cold climatic conditions, plant requirements are satisfi ed by means of physiological adaptations to prevent cells from freezing. Thus, the growth of woody plants in temperate regions slows down and they enter into a physiological state called dormancy. In order to identify the chilling and heat requirements to overcome the dormancy period of Cupressaceae pollen type in the south of Europe, we have carried out our study with aerobiological data from a 10-year (1996- 2005) period in Ponferrada, León (Spain). For the chilling requirements the best result was with a threshold temperature of 7.1ºC and an average of 927 CH. Calculation of heat requirements was carried out with maximum temperature, with 490 growth degree days (GDD) needed, with a threshold temperature of 0ºC. We have used the 2002-2003, 2003- 2004 and 2004-2005 periods in order to determine the real validity of the model. We have not used these years in developing the models. The dates predicted differ in only a few days from those observed: in 2002-2003 there was a difference of 11 days, in 2003-2004 predicted and observed dates were the same, but in 2004-2005 the difference obtained was of 43 days