Water relations of “trailing‐edge” evergreen oaks in the semi‐arid upper Yangtze region, SE Himalaya

Unlike the well‐understood cold limit of trees, the causes of the dry trailing edge of trees await explanation. Here we aimed at explaining the drought limit of an evergreen oak species (Quercus pannosa s.l.) in a typical dry valley of the upper Yangtze region, SE Himalaya, where rains (ca. 250 mm/a) are largely confined to the typical monsoon season (July–August) with drought during the remaining 9–10 months. We capitalized on an unintentional year‐round irrigation treatment with trees growing along the overflow of a water reservoir serving as moist controls. We measured shoot water potential (Ψ), leaf conductance (g), flushing phenology, leaf mass per area (LMA), foliar and stem δ13C, leaf nutrients, and non‐structural carbohydrates across the transition from non‐monsoon to monsoon season, from April to August 2018. At the dry site, Ψ and g were high during the monsoon but declined to