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

Abstract

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.

Keywords: Olea europaea; desertification; ecological impacts; economic impacts; species interactions.

Fig. 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).

Fig. 2.

Geographic distribution of olive as: (A) the observed distribution of olive in the Mediterranean Basin (red) superimposed on a shaded relief map with coloring based on satellite-derived land cover from Natural Earth (http://www.naturalearthdata.com/); and (B) map of FAO ecological zones (20) included in the domain of the analysis, with the histogram showing the proportion of the total olive area in A within the ecological zones. Color palette in B is from http://colorbrewer2.org/.

Fig. 3.

Example of the simulated phenology of olive and olive fly at each grid point. (A) Olive fruiting and olive fly infestation for the period 1991–2000 in a typical olive-growing area near Villacidro in the southern part of Sardinia, Italy (latitude: 39.428°N; longitude: 8.881°E). The fruit and fly dynamics for 1991 are expanded in the stippled area (B–D). Plotted data were extracted from a larger simulation for the period 1958–2000 based on daily weather from the ERA40 (reanalysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts) climate data downscaled for the Mediterranean region using the Protheus regional climate model (38).

Fig. 4.

Impact of climate warming on olive phenology and olive fly abundance in the Mediterranean Basin. (A) Change in olive bloom date (days) and (B) in olive fly abundance (cumulative pupae × 10³ tree⁻¹⋅y⁻¹) under the A1B scenario of 1.8 °C climate warming.

Fig. 5.

Bioeconomic multitrophic effects of climate warming on olive and olive fly in the Mediterranean Basin. (A) Predicted changes in olive yield (t ha⁻¹); (B) change in infestation by olive fly (% olive fruit attacked by the fly); and (C) change in profit (€ ha⁻¹) under the A1B +1.8 °C climate warming scenario. Statistical outliers are mapped as such for improving data visualization (SI Appendix, SI Materials and Methods) and were identified using the boxplot function in R (see www.r-project.org/). Full data intervals are [−1.5, 2.3] (A) and [−914.7, 3,000.0] (C).

Fig. 6.

Frequency distribution of net economic gains and losses in olive due to climate warming. Histograms illustrate the frequency distribution of net profit gains and losses in different subregions of the Mediterranean Basin (see maps of subregions in SI Appendix, Fig. S9). Change in profit values in histograms is mapped to color as in Fig. 5C.