Stress‐induced secondary leaves of a boreal deciduous shrub (Vaccinium myrtillus) overwinter then regain activity the following growing season

The ericoid shrub Vaccinium myrtillus is one of several deciduous boreal plants that respond to larval defoliation by compensatory production of a new set of leaves within the same growing season soon after defoliation. This new set is termed as ‘secondary leaves’. The physiological performance and longevity of secondary leaves is poorly understood. Following a multi‐year larval outbreak in boreal Norway, we therefore monitored the fate of the secondary leaves from 2014 to 2016. We observed that secondary leaves were still green upon onset of snow season and that the same leaves were still attached and green when snow melted in spring. During the early growing season of 2015, the overwintering leaves were consumed by moth larvae, but the secondary leaves produced in mid‐July 2015 overwintered and were not consumed by larvae the next growing season. Our monitoring shows that most of these leaves remained attached until late August, while the contents of chlorophyll and nitrogen remained ...