Cloud pattern and water relations in Picea rubens and Abies fraseri, southern Appalachian Mountains, USA

► Examined the impacts of fog on microclimate and plant physiology (Ψ) in spruce-fir forests. ► Frequent morning fog resulted in large reduction of PPFD and VPD with less effect on temperature. ► Fog days had an increase in Ψ from predawn to afternoon measurements, clear days a strong decrease. ► Juveniles of both species had stronger responses to changes in cloud pattern than adults. ► One of few studies demonstrating an increase in plant Ψ during a daily course.