Modelling leaf gas exchanges to predict functional trends in Mediterranean Quercus Ilex forest under climatic changes in temperature

A simple model based on the “big leaf” assumption and calibrated with field eco-physiological measures of gas exchanges is used to simulate the effects of temperature increase on net primary production, total canopy transpiration and the dimensionless decoupling coefficient Ω of Holm oak forests. Two different annual average air temperatures: 14.6 and 18.0 °C are considered, they are respectively the average current temperature and the one expected in the next 50 years in the Mediterranean area if the trend of global warming will continue. The model simulates the behaviour of the three parameters by assuming no changes in the effects of water constraints at both the temperatures. The model has been implemented by STELLA® II software. According to the model, the increase of air temperature affects both the net primary productivity (6.3%) and the water losses by canopy transpiration (37.2%). The model predicts an average decoupling factor, Ω, of about 0.26 at both temperatures of 14.6 and 18.0 °C. This value is in the range between Heathlands and Forest, suggesting that at the average annual temperature of 18.0 °C the Holm oak forest will start to respond in a similar way to more xeric plant communities.