Climate change and exotic pests and pathogens are main drivers of forest decline worldwide. In the Iberian Peninsula, this decline mainly affects evergreen Quercus species of high economic and ecological importance such as cork oak (Quercus suber) and holm oak (Quercus ilex). These species are threatened by the combined effects of the exotic soil-borne pathogen Phytophthora cinnamomi and a more arid climate. Phytophthora cinnamomi destroys the fine roots of the trees, limiting the absorption of nutrients and water. On the other hand, an increase in aridity implies stronger hydric stress in systems where water is already a limiting factor for plants. However, predicted reductions in precipitation could also negatively affect P. cinnamomi due to its dependence on free water for dispersal and infection. This could indirectly benefit holm and cork oaks, which would suffer less pathogen damage under drought conditions.

In order to determine the direct and indirect effects of drought and exotic pathogens on Q. suber performance, a group of researchers from the Institute of Natural Resources and Agrobiology of Seville (IRNAS-CSIC) in collaboration with researchers from the Universities of Córdoba, Jaén and Cádiz have carried out a study under greenhouse controlled conditions where they followed the growth of cork oak seedlings under 16 different combinations of soil moisture (simulating different climatic scenarios) and P. cinnamomi inoculum density.

Comparative of roots

Fig.1: Morphological differences in Q. suber plants under different treatments of soil moisture and Phytophthora cinnamomi inoculum density. Plants subjected to a 10% reduction in soil moisture content and high concentration of the pathogen (left) with respect to the average spring conditions and low concentration of P. cinnamomi (right).

The results of this study show novel interactive effects of drought and the exotic pathogen P. cinnamomi on cork oak growth. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased.

Thanks to this study, we can conclude that a precipitation reduction caused by climate change could imply sub-optimal conditions for P. cinnamomi infective capacity, reducing the damage caused to susceptible species and allowing for a slower advance of the disease in invaded areas. The results of this study have recently been published in the prestigious journal Agricultural and Forest Meteorology, and can be found here:


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