Fragmentation in holm oak forests attenuates water stress even under extreme drought

ALICIA FORNER SALES; ISMAEL ARANDA; TERESA MORÁN LÓPEZ; DULCE FLORES RENTERÍA; FERNANDO VALLADARES ROS

Sevilla

Congreso; XIV MEDECOS & XIII AEET congress; 2017

International Society of Mediterranean Ecology & AEET

Fragmentation and summer drought are two of the main threats to Mediterranean forests. More frequent extreme droughts overthe last decades have challenged plant tolerance to severe water stress and have increased alteration of natural habitats which arefurther compromising plant performance and survival. We hypothesized that trees at fragmented Mediterranean forests are sufferinghigher water stress during summer drought because they are more exposed to high radiation and temperatures due to edge effectsthat would prompt higher water losses by evapotranspiration. However, forest edges reduce intraspecific competition, allowing higherwater availability, and tempering water stress. To test the alternative hypothesis that fragmentation may not exacerbate water stressunder extreme drought in Mediterranean tree forests we monitored ecophysiological variables during two years in two holm oak(Quercus Ilex) forests archipelagos of the Iberian Peninsula. Water stress was highest in trees at forest interiors in both study forests.Trees at small forest fragments showed the highest predawn water potential, stomatal conductance and photochemical efficiency ofphotosystem II. During the intense summer drought those patterns were also observed and water stress was exacerbated much moreat the forest interiors. Our results rejected our hypothesis and demonstrated that fragmentation attenuated water stress even underextreme drought. This study highlight the relevance of addressing at a local scale the interaction of extreme drought events with otherdriving forces of global change to elucidate the real tree tolerance to severe water stress and therefore, the potential evolution ofMediterranean forests in future.