Impact of climatic conditions on the reproductive phenological phases of European hazel (Corylus avellana L.) in Slovakia

The work presents the results of phenological observations of flowering and fruit ripeness of the European hazel (Corylus avellana L.) in Slovakia in two time periods: 1964-1983, and 1994-2013. The phenological stations at elevations from 100 to 875 m a.s.l. were grouped to 7 elevation zones, each 100 m wide. In the first studied period, flowering started on 19 March on average, while in the second period it started 5 days earlier. The average duration of flowering equal to 7-9 days did not depend on the elevation, but on the air temperature and weather patterns in the different elevation zones. During the first period, the average elevation gradient of flowering was 5.6 days per 100 elevation meters, while in the second period it was reduced to 3.5 days in the entire elevation profile. In the elevation zones between 300 and 500 m, a high correlation (P < 0.01) between the onset of flowering and elevation was reduced to a moderate level of correlation due to changing environmental conditions. In 1994-2013, the ripeness of hazel nuts started on average on 30 August in Slovakia, showed low variability and moderate correlation with elevation. The phenological elevation gradient was 2.9 days per 100 m of elevation.