Oak trees use carbohydrate reserves to survive insect invasions

A new study from Harvard has revealed that a tree’s carbohydrate reserves are crucial to surviving insect outbreaks. According to the researchers, the biology of oak trees makes them resilient to even the most severe stressors. 

“Oak trees are planners, in a way,” explained study co-author Meghan Blumstein of MIT. “Some of the food they make during the growing season is used immediately for energy and some is stored in the stems and roots for a rainy day. With stored carbs, they are able to immediately create a new flush of leaves after an insect outbreak.”

In southern New England, a recent multi-year outbreak of an invasive moth killed thousands of acres of oak trees. For the investigation, the researchers focused on the trees that didn’t die. 

The experts pinpointed the exact threshold of reserves that were needed for survival : 1.5 percent carbohydrates in their dried wood, or about 20 to 25 percent of their normal storage capacity. 

The researchers found that back-to-back insect invasions from 2016 to 2018 challenged the resilience of the oak trees by defoliating them year after year.

“The trees that died were the trees that were out of reserves,” said study lead author Audrey Barker Plotkin, a Senior Scientist at the Harvard Forest. 

The location of the trees influenced survival as well. The research team found that trees growing along forest edges tended to have more reserves, even at the same level of defoliation, making them more resilient than interior forest trees. 

The Harvard study has produced some of the first direct evidence which confirms that trees can starve to death when insects invade. As new pests emerge and climate change continues, the findings from this research will help improve forest resilience models.

The study is published in the journal Functional Ecology.

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By Chrissy Sexton, Earth.com Staff Writer