Humans, key contributors to climate change, unknowingly depend on forests to combat the increasing carbon dioxide levels they are introducing into the atmosphere as levels are increasing more rapidly in the last 40 years than ever before.
“It has substantial consequences for climate, [creating a] greenhouse effect. So as you increase CO?, it traps more heat in the [atmosphere] of earth,” said Dr. John Couture of the University of Wisconsin—Madison’s Department of Forest and Wildlife Ecology.
Couture researched for three years, with his team, for a project called Aspen Free-Air Carbon dioxide and ozone Enrichment in Rhinelander, Wisconsin. Aspen FACE focused on how forests would respond to future levels of carbon dioxide, calculated to levels at the year 2050.
Trees grow by taking in carbon dioxide, converting it to a sugar and making that into a biomass. This process, therefore, is carbon driven, meaning that when more carbon dioxide is introduced into the atmosphere, the trees are able to grow larger. This data is then put into global vegetation productivity models which show how plant productivity will change with changes in climate, giving scientists, like Couture, an idea of what forests will look like in the future.
“Our research shows that the potential productivity of forests is, in some cases, cut in half,” Couture said. “If we’re trying to accurately model how much carbon forests can hold, and how much of a model they can be to anthropogenic carbon emissions, then we need to accurately characterize that as much as possible. What we’re suggesting is a missing piece.”
The missing piece? The impact of insects.
The hope is that forests will offset the increased levels of carbon dioxide in the atmosphere. However, recent discoveries have found that insects play a role in the amount of carbon dioxide trees can take up.
Insects, a main herbivore in the ecosystem, according to Couture, pose an unknown threat to the growth of trees in future environments.
The bugs, specifically leaf-eating caterpillars and leaf-eating beetles, cause two different types of damages to forests. Outbreak damages, which only occur about once every 10 years, cause large scale destruction to forests while the other type of damages are the day-to-day consumption of the trees by the insects for survival.
“In some cases, the outbreak damage is taken into account, but never is the day-to-day damage, which is the kind that the forest experiences all the time,” Couture said.
Couture’s research focuses on the shifts in the everyday damage and how they affect the future productivity of the forest. As atmospheric carbon dioxide levels increase, so do the day-to-day damages of the forest.
To explain why the bugs seemed to be increasing their consumption of the trees, Couture mentioned the tree itself.
“With more CO?, trees become more efficient, so they can spread their protein out, or they don’t need as much of it in one area to get the same growth rate. What that does is create less protein per area, so you basically dilute the protein,” said Couture. “Insects [to get all their nutrients must] eat more food.”
When predicting future carbon storage by forests, insects need to be included, according to Couture.
“Our results suggest that it will have a substantial impact in the future,” Couture said.