Climate-driven variations in productivity reveal adaptive strategies in Iberian cork oak agroforestry systems

Cork oak agroforestry systems (AFS) have been managed for centuries by humans to produce cork and other goods and services and have recently been recognised as an important reservoir for biodiversity improvement and conservation. However, despite having recently been included as a natural habitat of community-wide interest within the EU Habitats Directive, these systems are in a critical situation of decline. Among other factors, they are strongly threatened by climate change, the effects of which are also expected to be particularly severe in the Mediterranean region. In this study, we aimed to evaluate the influence of climate variability by examining primary production indicators and also to analyse whether the geographical location may have a role in the incidence of the adverse effects of climate. Cork oak AFS were identified in the Forest Map of Spain and the Land use map of Portugal and categorized on the basis of canopy cover. Seasonal climate data from 2001 to 2020 were used to model relationships with climate predictors and proximity to the coast. Hotspot analysis was conducted to identify significant spatial clusters of high- and low-efficiency areas. The responses to the influence of climatic conditions differed among the various cork oak AFS categories, particularly in the forest category, which was less dependent on climate variations. Relative humidity and water availability were the main drivers of net primary production (NPP). Carbon use efficiency (CUE) was limited by relative humidity and spring temperature in open ecosystems. Proximity to the coast proved beneficial, especially in years with adverse weather conditions, but was not a limiting factor for survival of the ecosystem. Finally, the results of the hotspot analysis supported the other findings, highlighting high-efficiency areas close to the coast and cold spots grouped in specific areas or dispersed inland. Canopy plays a key role in the influence of climatic conditions, particularly in forest categories in which a high density seems to generate microclimate conditions. Water availability, both via the soil and air moisture, is the main driver of primary production, reflecting different adaptive strategies. The oceanic atmosphere may act as a buffer in years of extreme drought.