Abstract
Climate change is expected to greatly alter and modify the ecological conditions of plant growth and distribution, particularly in the Mediterranean Basin, considered as one of the most vulnerable zone to global warming in the world. In this chapter, we look at the biogeography of the olive tree, an emblematic species of the Mediterranean Basin, represented in Morocco by two wild subspecies: Olea europaea subsp. europaea var. sylvestris, the ancestor of all the olive varieties and widely distributed in the country, and Olea e. subsp. maroccana, endemic in a restricted southwestern area. We hypothesis, within the context of future warming, an increase of O. e. subsp. e. var. sylvestris distribution area is expected, while for O. e. subsp. maroccana, an alteration of its distribution is predicted, increasing seriously the risk of extinction. In order to assess the current and future potential geographic distribution of the two wild olive species in Morocco, a species distribution based-modelling was performed to understand the relationships between species distributions and climatic factors, on the basis of field data and 19 climatic variables. Two representative concentration pathways, RCP4.5 and RCP8.5, were used to forecast the future distribution of the two wild olive subspecies in 2050 and 2070. To avoid multicollinearity, the highly correlated climatic variables (r > 0.9, Pearson correlation coefficient) were deleted from the independent variables list. The Jackknife test was carried out to evaluate the relevance of the climatic variables for predictive modeling. The maximum entropy model for the current distribution of both species provides a satisfactory result, with a high value of the Area Under Curve equal to 0.980 (±0.001) for Olea europaea subsp. europaea var. sylvestris and equal to 0.997 (±0.001) for Olea europaea subsp. maroccana. Jackknife test indicates that precipitation and temperature variables play a significance role in wild olive species biogeographical dynamics in Morocco. The study results confirm our hypothesis of an expansion of O. e. subsp. e. var. sylvestris suitable area and the threatened aspect of Olea e. subsp. maroccana under climate change scenarios. The approach used in this study is promising to predict the potential distribution of wild olive species, and can be an effective tool to support conservation and restoration programs