No risk-no fun: Penalty and recovery from spring frost damage in deciduous temperate trees

Phenological shifts in response to changing climatic conditions is a key acclimation process for the persistence of perennial plants in temperate and boreal climates. The optimal time to leaf-out is the result of an evolutionary process determined by the trade-off between minimizing the risk of freezing damages and herbivory pressure while maximizing resource uptake to increase competitiveness against the other plants. We quantified the penalty exerted by frost damage at the time of leaf emergence on plant development (reduction in leaf area, canopy duration and growth) over the potential gains without frost (increased biomass and non-structural carbohydrate reserves), depending on when leaf-out occurs. To this purpose, we exposed 960 saplings of four temperate deciduous tree species with contrasting cold hardiness to two frost intensities shortly after leaf emergence, which was artificially induced at four occasions to reflect the whole range of natural leaf-out dates. One year above-ground biomass (AGB) increments following the frost revealed a clear ranking among the species depending on their strategy to cope with damaging frosts. Prunus avium (-41% of AGB-increment compared to control saplings) resprouted from the stem base, Quercus robur (-62%) rapidly produced new leaves from dormant reserve buds, Fagus sylvatica (-98%) showed highest chlorophyll content in autumn and delayed senescence together with Carpinus betulus (-105%), which overcompensated NSC reserves after the growing season but showed highest mortality (up to 32%). In all species, NSC reserves recovered rapidly to control levels at the expense of growth. The timing of leaf-out (advanced and delayed artificially) significantly affected the performance and recovery (regreening and growth) of both frozen and non-frozen saplings, with the lowest performance found at the most delayed leaf-out date. We propose that the potential to recover from frost damages is an important component of a tree's performance, particularly at the juvenile stage. The ability to recover may become even more decisive in the future with the predicted increase of false springs in many extratropical regions. Read the free Plain Language Summary for this article on the Journal blog.