Climate change is clearly influencing deciduous trees by prompting leaves to emerge earlier in the season. Yet the danger of late spring frosts remains substantial, and the frequency of extreme droughts is rising. Species capable of quick recovery after frost damage may fare better in the future and cope more effectively with cold snaps. This insight comes from a study conducted by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).
Late spring frosts have long posed a risk to deciduous trees, particularly when they strike as new leaves unfold, a stage that is especially sensitive to temperature shifts and freezing events.
“While frost damage is a frequent topic, its actual impact on our trees isn’t entirely clear,” notes one of the researchers, Frederik Baumgarten. The study also investigates why some trees shed leaves earlier than others and how climate change could influence this pattern. Baumgarten and colleagues designed an outdoor experiment to find answers.
In the setup, 960 two-year-old trees from four local species were planted in pots: wild cherry (Prunus avium), oak (Quercus robur), hornbeam (Carpinus betulus) and beech (Fagus sylvatica).
Baumgarten then placed the trees in a heat chamber for several days at weekly intervals to mimic a spring period, causing them to bloom at slightly different times compared with control trees left to develop under natural conditions.
Resistance of cherry and oak trees
Shortly after leaf emergence, the researcher subjected the trees to artificial frost in a cold room at two densities, designed to induce leaf death. The trees were then transplanted outdoors and monitored for a full year to observe recovery and growth.
Deeper frost exposure led to stronger damage in some cases. Without any freezing treatment, growth was still delayed relative to earlier stages already in progress. In a forest setting, these trees may be outcompeted by other individuals and species, the report notes.
Some samples showed increased biomass after frost exposure, though aphid attacks affected certain species. The authors concluded that the optimal timing for leaf appearance in spring varied among species when comparing the responses across the two experimental boundaries.
Frost damage weakens trees, yet the experiments revealed that frost is not equally harmful across species. “I was surprised by how well some species managed frost damage,” says Baumgarten. All trees that experienced frost grew more slowly than those that did not, but wild cherry and oak demonstrated effective strategies to cope with early frost events.
Wild cherry trees formed new shoots, and oaks produced numerous replacement buds that could open quickly if the first leaves died. Mortality in these two species remained low.
In contrast, hornbeam fared poorly: about 32% could not withstand the frost. Mortality among beech-related trees was also notable, with about 12% affected. The survivors showed smaller leaves and thinner crowns than usual.
Danger of ‘false bow’
The study demonstrated that the ability to survive frost allows species such as oak and wild cherry to develop leaves earlier in the year despite frost risk. Climate trends may heighten the importance of this ability in the future since warmer springs lead to earlier leaf-out in many deciduous trees, creating a phenomenon the authors describe as a “false spring.”
Researchers warn that late frosts may persist as extreme events, and frost-resistant species could be better prepared to endure such shocks, particularly when another stressor, like drought, occurs in the same year. These dynamics could reshape forests over time as species better adapted to frost establish themselves.
The results of the experiment were published in the journal Functional Ecology. This work provides a window into how forest communities might reassemble under changing climate conditions.
Frosts can weaken plant function by reducing enzymatic activity, lowering respiration and photosynthesis rates, and impairing water uptake. Such disruptions disrupt the balance of physiological processes like respiration, photosynthesis, transpiration, water transport, and growth. In the most sensitive phenological stages, such as flowering and fruit set, frost damage can be especially costly.
Reference note: CITATION: Functional Ecology, Baumgarten et al. — Recovery patterns of temperate trees under frost stress in a warming world.
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