Source: French to English Tester Published on: 2026-05-01
Source: The Conversation – in French– By Andreas Prinzing, Professor
When oaks are severely damaged by caterpillars in one year, they open their buds later the following spring. Our international research team has shown that this strategy is very effective against their predators. We have just published our results in the journalNature Ecology & Evolution.
In the spring in the forest, many caterpillars hatch precisely when the leaves of the trees are still young and tender. In this way, they find a table abundantly set.
If oaks are heavily infested by caterpillars in a given year, they react the following spring: they delay the appearance of their leaves by three days. This is unfavorable to the caterpillars. After hatching, they find themselves literally facing empty plates, because the oak leaves are still well hidden inside the buds.
This strategy is very effective: in some species, all the caterpillars die after three days without food. As a result, this delayed hatching strategy reduces the damage caused by their feeding on the tree by 55%.
How have we seen, from space, how the oaks fight the caterpillars?
To demonstrate these links, we used advanced interdisciplinary methods from ecology and remote sensing. Previously, researchers had to laboriously observe individual trees in the field. For this study, however, an area of 2,400 square kilometers in Northern Bavaria was continuously monitored thanks to data from the Sentinel-1 satellite. What makes these radar satellites special is that they provide precise data on the state of canopies, even under thick cloud cover.
We analyzed a total of 137,500 individual observations over five years, from 2017 to 2021. The satellites provided data with a resolution of 10×10 meters per pixel, which corresponds approximately to the canopy (the part of a tree consisting of a structured set of branches located at the top of the trunk) of a single tree. In total, 27,500 pixels of this type were analyzed across 60 forest areas.
The year 2019 proved to be particularly instructive, as the region experienced a massive invasion of the spongy moth (a pest of deciduous forests). Radar sensors precisely recorded which trees lost their leaves and how they reacted the following year.
Why is this discovery important?
Trees do not only respond to the weather in spring. This delaying tactic is more effective for the oak than a chemical defense, such as the bitter tannins present in the leaves. Indeed, the tree would have to spend a lot of energy to increase its production of tannins.
For the first time, the study conclusively explains why, on average, the forest does not green as quickly as temperatures might suggest. Previous computational models often inaccurately estimate the state of forests because they exclusively consider climatic factors such as temperature and ignore biological interactions between plants and insects.
Trees are engaged in a kind of evolutionary tug-of-war: while the increase in temperatures linked to climate change pushes them to produce their leaves earlier and earlier, the pressure exerted by herbivorous insects forces them to delay this process. A key advantage of this delaying strategy is that it is temporary and reversible. Since trees only delay leafing after a real infestation, the insects cannot adapt to it permanently. This dynamic interaction is an example of the great resilience and adaptive capacity of forests in a changing world.
What are the prospects?
Future experiments should allow a better understanding of the importance of these mechanisms for patterns explained for decades by other mechanisms, as well as the consequences for the interactions of trees with their mycorrhizal symbionts and with the enemies of their enemies, such as tits and parasitic wasps.
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The authors do not work for, advise, hold shares in, or receive funds from any organization that could benefit from this article, and have declared no other affiliation than their research institution.
–ref. How oaks thwart caterpillars by delaying the opening of their buds –https://theconversation.com/how-oaks-outsmart-caterpillars-by-delaying-the-opening-of-their-buds-281952