Leaf-out in northern ecotypes of wide-ranging trees requires less spring warming, enhancing the risk of spring frost damage at cold range limits

Aim. Trees need to avoid frost damage to their young leaves by leafing out after the occurrence of the last frost, yet they also need to start photosynthesis early in the season to achieve sufficient growth. This trade-off leads to the hypothesis that ‘safety margins’ against spring frost should become shorter, the longer the winter duration, perhaps reaching an asymptotic limit where frost damage would occur in most years. Physiologically, shorter safety margins in high-latitude ecotypes might be achieved by lower degree-day requirements for leaf-out, compared to low-latitude ecotypes.

Location. Europe 

Time period. 1902–2009

Major taxa studied. Temperate trees. 

Methods. Using herbarium collections of Acer platanoides, Carpinus betulus, Fagus sylvatica, and Prunus spinosa made over 108 years at 40 to 60o N latitude, we related historic leaf-out dates to winter and spring temperatures (chilling and degree-days), winter duration, and date of last frost occurrence in the rele...