Fine-scale ecological and economic assessment of climate change on olive in the Mediterranean Basin reveals winners and losers

The Mediterranean Basin is a climate and biodiversity hot spot, and climate change threatens agro-ecosystems such as olive, an ancient drought-tolerant crop of considerable ecological and socioeconomic importance. Climate change will impact the interactions of olive and the obligate olive fruit fly (Bactrocera oleae), and alter the economics of olive culture across the Basin. We estimate the effects of climate change on the dynamics and interaction of olive and the fly using physiologically based demographic models in a geographic information system context as driven by daily climate change scenario weather. A regional climate model that includes fine-scale representation of the effects of topography and the influence of the Mediterranean Sea on regional climate was used to scale the global climate data. The system model for olive/olive fly was used as the production function in our economic analysis, replacing the commonly used production-damage control function. Climate warming will affect olive yield and fly infestation levels across the Basin, resulting in economic winners and losers at the local and regional scales. At the local scale, profitability of small olive farms in many marginal areas of Europe and elsewhere in the Basin will decrease, leading to increased abandonment. These marginal farms are critical to conserving soil, maintaining biodiversity, and reducing fire risk in these areas. Our fine-scale bioeconomic approach provides a realistic prototype for assessing climate change impacts in other Mediterranean agro-ecosystems facing extant and new invasive pests.The Mediterranean Basin is a climate change (1) and biodiversity (2) hot spot where substantial warming is predicted in the next few decades (3). A 2 °C increase in average temperature is a widely used metric for assessing risks associated with global warming and as a policy reference, and this level of warming will likely occur in the Basin between 2030 and 2060 (4) with unknown biological and economic impact on major crop systems. Small differences in average climate warming are predicted for the Basin by A1B and higher greenhouse-gases (GHG) forcing scenarios within the 2050 time horizon (5).A major agro-ecosystem in the Basin is olive (Olea europaea L.), an ancient ubiquitous crop of considerable socioeconomic importance (6). A detailed review of methods used to assess the impact of weather and of climate change on the olive system is given in SI Appendix. Most of the crop is used to produce olive oil, with Basin countries producing 97% of the world supply (International Olive Council, www.internationaloliveoil.org/). Olive is a long-lived drought-tolerant species limited by frost and high temperatures, and to a lesser extent by low soil fertility and soil water (7). Temperatures <−8.3 °C damage olive and limit its northward distribution, whereas annual rainfall <350 mm y⁻¹ limits its distribution in arid regions. Commercial olive production occurs in areas with >500 mm rainfall y⁻¹ (SI Appendix, Fig. S1). Climate models predict increased temperatures for the Mediterranean Basin in response to increasing GHG], but only a weak negative trend in precipitation and no trend in evaporation are predicted (8). Growth rates in some plants will increase with CO₂] within their thermal and moisture limits (7, 9), but the response for olive is unknown.Mainstream assessments of climate change impact on agricultural and other ecosystems have omitted trophic interactions (10). Here we include the effects of climate change on olive phenology, growth, and yield, and on the dynamics and impact of its obligate major pest, the olive fruit fly Bactrocera oleae (Rossi)]. The thermal limits of olive and the fly differ and affect the trophic interactions (11) crucial to estimating the bioeconomic impact of climate change in olive across the Basin.Previous assessments of climate change on heterothermic species have used ecological niche modeling (ENM) approaches that characterize climatically a species’ geographic range based on observed aggregate weather data in areas of its recorded distribution (for olive, see, e.g., ref. 12). ENMs are often used to predict the distribution of the species in response to climate change (13) despite serious deficiencies including the inability to include trophic interactions (14). Moreover, the implicit mathematical and ecological assumptions of ENMs hinder biological interpretation of the results (15).As an alternative we use mechanistic physiologically based demographic models (PBDMs) that explicitly capture the weather-driven biology of interacting species (e.g., ref. 16) and predict the geographic distribution and relative abundance of species across time and space independent of species distribution records using extant and climate change weather scenarios as drivers for the system. The explicit assumptions in PBDMs have heuristic value, and bridge the gap between long run field experiments used to study global change biology and the narrow methodological and conceptual bases of ENM approaches commonly used in macroecology (17, 18). These attributes are essential for assessing the bioeconomic consequences of climate warming on trophic interactions across large landscapes.Linked PBDMs for olive and olive fly in a geographic information system (GIS) context (11) (Fig. 1 and SI Appendix, Fig. S2) are used to estimate the fine-scale ecological and economic impact of climate warming on olive yield and fly infestation across the Basin using baseline daily weather (scenario ) simulated under observed GHG], and the increasing GHG] A1B emissions scenario () of the Intergovernmental Panel on Climate Change (IPCC) (Materials and Methods and SI Appendix, SI Materials and Methods).Open in a separate windowFig. 1.Multitrophic biology of the olive/olive fly system. (A) Dry matter flow in olive and to olive fly, and (B) dynamics of olive fly number (see ref. 22).