Temperature influence on the flowering of Quercus in the South of Galicia (Ourense and Vigo, 1994-98)

Abstract

Plant requirements in order to survive periods of adverse climatic conditions are satisfied by means of physiological adaptions. Thus, woody plants in temperate regions, in order to prevent the water in their cells from freezing, slow their growth down almost to a standstill, entering into a physiological state called "dormancy". Many authors indicate that the end of the dormancy phase require a period of low temperatures followed by another of relatively warm temperatures. When the cold and the heat accumulations are fullfilled, pollination occurs. The objective of this study is to ascertain the influence that a climatic parameter such as temperature exerts on Quercus in the south of Galicia, in order to identify the start of the dormancy period, its duration and the consequents cold and heat requirements that triggers flowering. In this regard, we chose two arcas, since they have different temperature patterns, ranging from mild in the case of Vigo to cold in that of Ourense. Monitoring in the two stations was carried out by means of a 7-day LANZONI VPPS 2000 pollen trap, based on the Hirst pollen trap. Quercus began its pollination period in the month of March. In Vigo flowering took place during the first fifteen days and a few days later in Ourense. During the four years under study, in order to overcome the dormancy period, Ourcnse needed an average of 778 chilling hours (CH) and Vigo had a minor chilling accumulation with only 458 CH. In the case of heat accumulation, we found that Ourense had the smallest requirement and Vigo the largest, thus Ourense needed an average of 352 GDD (Growth Degree Days) and Vigo around 450 GDD.