Leaf-out in northern ecotypes of wide-ranging trees requires less spring warming, enhancing the risk of spring frost damage at cold range limits
Zohner, Constantin; Mo, Lidong; Sebald, Veronica; Renner, Susanne S (2021), Leaf-out in northern ecotypes of wide-ranging trees requires less spring warming, enhancing the risk of spring frost damage at cold range limits, Dryad, Dataset, https://doi.org/10.5061/dryad.pg4f4qrjz
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.
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 relevant years and locations.
Results. In all species, frost safety margins decreased towards high-latitude regions with long winters, with each day increase in winter duration reducing frost safety margins by 0.48 days in Fagus and 0.32–0.21 days in Prunus, Acer, andCarpinus. These latitudinal differences correlate with northern ecotypes’ shorter degree-day requirements for leaf-out.
Main Conclusions. The decline in spring-frost safety margins in regions with long winters supports the new hypothesis that species may reach their geographic range limit where they ‘bump up’ against experiencing regular frost injury to their young leaves. Larger datasets are necessary to further corroborate our hypothesis and future efforts should thus be directed toward increasing the latitudinal range of existing phenological databases.
Leaf-out dates in Acer platanoides, Carpinus betulus, Fagus sylvatica, and Prunus spinosa were inferred from herbarium specimens in seven herbaria (Aarhus University herbarium, AAU; Berlin herbarium, B; Copenhagen herbarium, C; Florence herbarium, FLO; Munich herbarium, M; Herbarium Senckenbergianum Frankfurt, F; Stockholm herbarium, S). While all specimens of these species were photographed, only specimens in the initial leaf-out stage were used for further analysis, which was defined as (1) not all leaves entirely unfolded and (2) leaves not yet full sized (Everill et al., 2014; Zohner and Renner, 2014). For specimens that met these criteria, we recorded species name, collection date, and collection location. Only low-elevation sites (<800 m a.s.l.) were included to remove climate variation due to elevational gradients. This resulted in a total of 392 leaf-out dates (84 Fagus sylvatica, 136 Prunus spinosa, 82 Carpinus betulus, and 90 Acer platanoides) covering the years 1902 to 2009 (data available in Supplementary Table 1).
Deutsche Forschungsgemeinschaft, Award: RE 603/25-1