First phenological and aerobiological assessment of olive orchards at the Northern limit of the Mediterranean bioclimatic area

An increase in the cultivation of olive trees was prompted in the Northwestern Spain during recent years favored by the agricultural politics in the region. The aim of this study is to know the phenological and aerobiological behavior of the olive trees at the northern limit of the Mediterranean bioclimatic area in order to determine their thermal requirements for the development of predictive agro-phenological models for two varieties (Arbequina and Frantoio) of the new olive cultivated areas. The BBCH scale was used for the phenological observations. Chill accumulation during dormancy and heat requirements to overcome the successive phenological stages were calculated following different methods. To complete the phenology predictive models, the Mitscherlich’s monomolecular equation was applied. The monitoring of the atmospheric pollen content was conducted by means a volumetric pollen Hirst trap placed in the middle of the plot. The period of chilling accumulation was completed during the first fortnight of January with an average of 654 chilling hours and a base temperature of 7.5 °C. Considering the duration of the vegetative olive cycle around 2390°GDD (growing degree days) was necessary to overcome the ripening of berries. The proposed model for the prediction of the successive ecological events showed a deviation between 1.5 and 3.5 days on the phenological scale. The presence of Olea pollen grains in the atmosphere of the olive grove was registered during stage 5 and stage 6 (flowering). The Hybrid Single Particle Lagrangian Integrated Trajectory Models confirmed that pollen peaks during the previous days to the flowering stage came from the extensive olive groves of the Northern Portugal which flowers some days in advance.