Drivers of irrigated olive grove expansion in Mediterranean landscapes and associated biodiversity impacts

Over the last 30 years, olive farming has experienced a fast and large-scale intensification process across its Mediterranean range, that is reshaping Mediterranean farmland landscapes with associated impacts on biodiversity and ecosystem services. This study aims to analyze irrigated olive grove spatial expansion patterns across a 27–year period in a region of Southern Portugal, by exploring its drivers, describing the involved land-use dynamics, and to evaluating its potential biodiversity impacts. Land cover spatio-temporal dynamics were characterized by comparing recent land cover maps 2017 with those before the intensification upsurge (1990), using a grid of sampling points across the area. To investigate the drivers of intensification, these points were characterized using 10 variables reflecting policy context, previous land use (in 1990), biophysical features, and farm structure, which were used to model land cover transitions resulting in intensive olive farming. Finally, we used a counterfactual approach to assess the impacts of the olive intensification process on biodiversity in relation to alternative land cover change pathways, using farmland birds as an indicator group. We confirmed a large-scale expansion of irrigated olive groves in the region between 1990 and 2017, from being practically absent to covering ca. 6% of the study area. This expansion was made mostly at the expenses of open rainfed annual crops (63%) and, to a lesser degree, traditional rainfed olive groves (21%). Change was driven mainly by the combined effect of the availability of public irrigation water and large farms, although other factors related to legal constraints to land-use change, biophysical context and previous land management were also involved. During the study period, land cover transitions conducting to intensive olive farming were the most harmful for biodiversity, when compared to alternative land cover change pathways. By providing a quantitative insight into the underlying mechanisms and environmental consequences of the olive farming intensification process currently affecting biodiversity-rich Mediterranean farmland landscapes, our study contributes with valuable information that can be used by policy makers to better plan and manage the on-going expansion of intensive olive farming.