Abstract
The calibration of a reliable phenological model for olive grown in areas characterized by great environmental heterogeneity, like Italy, where many varieties exist, is challenging and often suffers from a lack of observations, especially on budbreak. In this study, we used a database encompassing many phenological events from different olive varieties, years, and sites scattered all over Italy to identify the phases in which site-enlarged developmental rates can be well regressed against air temperature (Developmental Rate function, DR) by testing both linear and nonlinear functions. A K-fold cross-validation (KfCV) was carried out to evaluate the ability of DR functions to predict phenological development. The cross-validation showed that the phases ranging from budbreak (BBCH 01 and 07) to flowering (BBCH 61 and 65) and from the beginning of flowering (BBCH 51) to flowering can be simulated with high accuracy (r2 = 0.93–0.96; RMSE = 3.9–6.6 days) with no appreciable difference among linear and nonlinear functions. Thus, the resulting DRs represent a simple yet reliable tool for regional phenological simulations for these phases in Italy, paving the way for a reverse modeling approach aimed at reconstructing the budbreak dates. By contrast, and despite a large number of phases explored, no appreciable results were obtained on other phases, suggesting possible interplays of different drivers that need to be further investigated.
Highlights
Olive (Olea europaea, L.) is a long-lived, drought-tolerant species strongly adapted to the Mediterranean climate [1], where it is counted among the oldest and most important tree crop species [2]
Temperature is the most influencing driver controlling the phenology of olive trees, especially flowering, for which a positive, mostly linear, relationship has been confirmed by a large number of studies [4,5,6,7,8,9]
We argued that if the temperature is the most influencing driver controlling the phenology of olive trees, an approach that explores its predictive power over many phases embracing a heterogenic pool of data could help overcome the problems arising from the environmental and genotypic diversity
Summary
Olive (Olea europaea, L.) is a long-lived, drought-tolerant species strongly adapted to the Mediterranean climate [1], where it is counted among the oldest and most important tree crop species [2]. In this region, temperatures lower than −8 ◦ C limit its northward distribution, whereas annual rainfalls lower than 350 mm y−1 limit its distribution in arid regions [1,3]. Temperature is the most influencing driver controlling the phenology of olive trees, especially flowering, for which a positive, mostly linear, relationship has been confirmed by a large number of studies [4,5,6,7,8,9]. In different bioclimatic areas, large variability in the likely chilling period could emerge [11]
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