Effects of topography and crown-exposure on olive tree phenology

The importance of the olive tree phenology from agricultural and ecological point of view justifies the need to carry out phenological studies at local and regional scales. Furthermore, flowering phenology in the olive tree (Olea europaea L.) is an important indicator of climatic change in the Mediterranean region. In this paper, we study the effects of altitude and the exposure of crown-flowering branches on the flowering phenology of the olive tree. The study was carried out from 2009 to 2012 at eight sites of Cornicabra olive cultivar in central Spain (Toledo province, Castilla-La Mancha region), at altitudes between 440 and 875 m above sea level, since most olive groves in central Spain are to be found in this altitude range. Flowering phenology was also compared in two olive groves located at the same site and elevation; one in a flat area and the other on a north-facing hillside. Results revealed a significant correlation between altitude and flowering start-date: for each 100 m increase in altitude, flowering started 2.5 days later. Analysis of individual flowering branches of the same tree showed that preflowering and flowering started several days later on north-facing compared to south-facing branches. Olive trees growing on a north-facing hillside started the preflowering stage with some delay with respect to those growing in flat areas. Finally, taking onset of flowering as the variable, a hierarchical cluster analysis enabled olive-groves to be classified by flowering sequence across an altitudinal gradient.