Olive phenology as a sensitive indicator of future climatic warming in theMediterranean

Experimental and modelling work suggests a strong dependence of olive flowe ring date on spring temperatures. Since airborne pollen concentrations refl ect the flowering phenology of olive populations within a radius of 50 km, they may be a sensitive regional indicator of climatic warming. We assessed this potential sensitivity with phenology models fitted to flowering dates inferred from maximum airborne pollen data. Of four models tested, a therm al time model gave the best fit for Montpellier, France, and was the most e ffective at the regional scale, providing reasonable predictions for 10 sit es in the western Mediterranean. This model was forced with replicated futu re temperature simulations for the western Mediterranean from a coupled oce an-atmosphere general circulation model (GCM). The GCM temperatures rose by 4.5 degrees C between 1990 and 2099 with a 1% per year increase in greenho use gases, and modelled flowering date advanced at a rate of 6.2 d per degr ees C. The results indicated that this long-term regional trend in phenolog y might be statistically significant as early as 2030, but with marked spat ial variation in magnitude, with the calculated flowering date between the 1990s and 2030s advancing by 3-23 d. Future monitoring of airborne olive po llen may therefore provide an early biological indicator of climatic warmin g in the Mediterranean.