Temperature requirements of Alnus pollen in Spain and Italy (1994-1998)

Woody plants in temperate regions, in order to prevent the water in their c ells fi om freezing, interrupt their growth entering into a physiological s tate called "dormancy". Trees also have a heat requirement that must be ful lfilled before actual growth is resumed and pollination occurs. The objective of this study is to ascertain the influence that a climatic p arameter such as temperature exerts on Alnus, in order to identify the star t of the dormancy period, its duration and the consequent heat requirement that triggers flowering in three European regions located at the same latit ude. In this regard, we chose two areas in Spain (Vigo and Santiago dr Comp ostela) and one in Italy (Perugia), since they have different temperature p atterns, ranging from mild in the case of Vigo to cold in that of Perugia, including an intermediate temperature pattern (Santiago). Monitoring in the three stations was carried out by means of a 7-day Lanzon i VPPS 2000 pollen trap. Alnus began its pollen season between the second and third week of January in Spain, while in Italy it began during the first week of February. During the four years under study, in order to overcome the dormancy period , Perugia needed an average of 962 chilling hours (CH), Santiago 622 CH. an d Vigo had the smallest chilling accumulation with only 460 CH. In the case of heat accumulation, we found that Perugia had the smallest requirement a nd Vigo the largest, thus Perugia needed an average of 42 (growth degree da ys) GDD, Santiago around 50 GDD and Vigo 61 GDD.