Increased autumn productivity permits temperate trees to compensate for spring frost damage

Climate warming is leading to earlier budburst and therefore an increased risk of spring frost injury to young leaves. But to what extent are second-cohort leaves, which trees put out after leaf-killing frosts, able to compensate incurred losses? To investigate whether second-cohort leaves behave differently from first-cohort leaves, we exposed saplings of beech (Fagus sylvatica), oak (Quercus robur), and honeysuckle (Lonicera xylosteum) to experimental treatments mimicking either a warm spring or a warm spring with a leaf-killing frost. Refoliation took 48, 43, and 36 d for beech, oak and honeysuckle, respectively. In beech and oak, autumn Chl content and photosynthesis rates were higher in second- than in first-cohort leaves, senescence in second-cohort leaves occurred c. 2-wk-later, and autumn bud growth in beech was elevated 66% in frost-damaged plants compared with the warm spring treatment. No differences in autumn phenology and growth were observed for honeysuckle. Overall, in beech and oak, delayed Chl breakdown in second-cohort leaves mitigated 31% and 25%, respectively, of the deficit in growing-season length incurred by spring frost damage. These results reveal an unexpected ability of second-cohort leaves of beech and oak to compensate for spring frost damage, and demonstrate that long-lived trees vary their autumnal phenology depending on preceding productivity.