Oak Trees Can Delay Sprouting Leaves to Defeat Caterpillars

New research reveals oak trees deliberately delay budburst - the timing of leaf emergence - in order to avoid being overwhelmed by hungry caterpillars, after it happened the previous year.

Comparison: The oak tree on the right was more heavily infested with caterpillars last year | Sven Finnberg / University of Würzburg

The trees’ remarkably clever tactic to defend themselves against potentially deadly predators was detected by scientists in Germany using precise imaging data from satellite.

They found that many insects, particularly caterpillars, hatch in the Spring just when the trees’ nutrient-rich leaves are still young and soft - and an ample food source. But if oak trees are heavily infested by caterpillars in a given year, they cunningly react the following Spring by delaying their leaf emergence by three days.

That means the caterpillars have nothing to eat after hatching because the oak leaves are still firmly wrapped up in their buds. The strategy is “highly effective” because the three day delay is sufficient to significantly reduce the pesky insects’ survival rate - and reduce the damage to the tree by 55 percent, according to a study published this month in the journal Nature Ecology and Evolution.

“This discovery fundamentally changes our previous understanding of the onset of spring in the forest," said lead author Dr. Soumen Mallick, of the University of Würzburg, Germany. “It shows that trees do not merely react passively to the weather in timing their leaves to emerge but also respond flexibly to biological threats.”

The researchers say their findings conclusively explain, for the first time, why in some Springs the forest does not turn green as quickly as temperatures would generally indicate that they should.