S16 - Session O2 - Modelling fruit trees in agroforestry systems: an attempt to upscale from tree to system scale

Authors: Nicolas Barbault *, Christian Dupraz, Pierre-Eric Lauri , Marie Gosme

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 very 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 is able to simulate agroforestry systems in three dimensions according to interactions between trees and crops for water, nitrogen and light. However, this model was developed and is parameterised only for forest trees, not fruit trees for which the balance between the vegetative and the fruit compartment is crucial. For its adaptation to olive-based agroforestry systems, several processes occurring at tree scale must be taken into account to model the system's response to environmental conditions. Here, we focus on two important parameters: the maximum number of fruits per leaf area and the maximum daily carbon allocation to fruits, that are key for the fruit-setting module and the carbon allocation module, respectively. The maximum fruit load was estimated at 1356 fruits per m 2 leaf area. To determine the maximum daily carbon allocation to fruits, we hypothesized a cultivar effect. Nine olive trees with a low fruit load were selected from 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/day) varied significantly between 'Leccino' and 'Cypressino' (3.9 10 -3 and 4.3 10 -3 , respectively) and 'Manzanille' (7.3 10 -3 ). These first results are now integrated in the Hi-sAFe model (as either species or varietal parameters) with the objective to test innovative olive-based agroforestry systems optimizing resource sharing between olive and annual crops.