Parametrization of an agroforestry model: from forest trees to olive trees

The conventional cultivation of olive trees can lead to environmental degradations such as soil erosion and loss of biodiversity. Agroforestry systems could bring solutions to these environmental degradations. A simulation model able to represent the growth and interactions between olive trees and annual crops would be useful to rapidly test and evaluate innovative olive-based agroforestry systems without the need for space and time-consuming field experiments. The Hi-sAFe model simulates agroforestry systems in three dimensions according to interactions between forest trees and annual crops for water, nitrogen and light. However, this model was developed and parameterised only for forest trees and not for fruit trees whose balance between the vegetative and the fruit organs is crucial. Two main adaptations were made to the model to simulate olive-based agroforestry systems: the addition of a fruit-setting module and the carbon allocation module adaptation. Here, we present the experimental estimation of two important parameters of these modules, both at tree scale: the maximum number of fruits m-2 leaf area and the maximum daily carbon allocation to fruits. The maximum fruit load per olive trees was estimated at 1356 fruits per m(2) leaf area using three genotypes of an ' Arbequina' x 'Oliviere' progeny. To determine the maximum daily carbon allocation to fruits, we hypothesized a cultivar effect. For these reason, nine olive trees, of three cultivars ('Leccino', 'Cypressino' and 'Manzanille'), with a low fruit load were selected from the three cultivars, and samples of fruits were dry-weighted every week for 12 weeks during fruit growth. The maximum daily carbon allocation to fruits (g carbon olive(-1) day(-1)) varied significantly between 'Leccino' and 'Cypressino' (3.9x10(-3) and 4.3x10(-3), respectively) and 'Manzanille' (7.3x10(-3)). The value of these two parameters not identifiable in the literature can be set to 1356 fruits m(-2) of leaf area (maximum number of fruits m-2 leaf area) and at 7.3x10(-3) g carbon olive(-1) day(-1) (maximum daily carbon allocation to fruits).