Revisiting Planting Density in Rainfed Olive: Yield, Water Productivity and Resilience in Different Mediterranean Regions.

Across the Mediterranean, most olive orchards are still rainfed and have traditionally been planted at low density on the assumption that wide spacing buffers the risk of crop failure in dry years. We tested this assumption with the process-based model OliveCan, simulating three planting densities (100, 204 and 408 trees ha-1) at three contrasting sites (Córdoba, Izmir and Pisa) on shallow and deep soils under a baseline climate and two perturbations (+2 °C and -10% rainfall). Increasing density raised both yield and water productivity (WPy, the yield-to-evapotranspiration ratio) in all studied scenarios. As density increases, soil evaporation (Es) and runoff are reduced, and more water can be used for transpiration (Ep). Our analysis suggests that yield gains overcome Ep rises when tree density increases, resulting in a better WPy. Deep soils out-yielded shallow ones and buffered climatic stress. Yields were robust to a moderate, evenly distributed rainfall reduction but were eroded by warming. A stability analysis showed the highest density to be the most productive across the studied site × climate scenario × simulation year × soil depth combinations, while the lowest planting density was more stable. The present work explores new possibilities for rainfed olive farmers. Fieldwork would help test the results presented here and tailor new tree densities for rainfed olive orchards.