Assessing agroclimatic requirements and modeling olive phenophase events in warm and sub-arid climate areas

Forecasting phenological events has important uses in warm Mediterranean area, where olive is one of the oldest cultivated species.Thus, continuously-recorded phenological observations for the main olive cultivar Chemlali widely spreading in warm and sub-arid area were achieved during 2005–2019 in central Tunisia. Gathered climatic and phenological data were used to: i) delineate the chill and heat accumulation periods and the thermal requirements using Partial Least Squares (PLS) approach; and to ii) develop statistical models predicting budburst and flowering dates. Results revealed significant yearly variations in budburst and flowering dates related to the climatic conditions. PLS analysis delineated two chill accumulation periods spanned from November 19th to January 12th and from the end of March to the beginning of April, respectively. Stepwise regression revealed that the best indicator of the budburst date was the mean temperature in pentad-6 of November followed by the minimum and the mean temperature during pentad-2 of February. Based on these two statistical analyses, chilling requirements seemed to be linked to the first delineated chill accumulation period. Average chilling and heat requirements of ‘Chemlali’ olive cultivar were 17 CP and 24892 GDH, respectively. A forecasting linear model was generated displaying mean absolute error of 1.6 and 2.4 days between simulated and observed budburst and start flowering dates, respectively. These proposed models will be very helpful for orchard management and the high number of independent factors determining the critical periods necessary for flowering may explain the adaptive plasticity of ‘Chemlali’ cultivar growing in sub-arid and warm areas.