New research sheds light on relationships between plants and insects in Kaua‘i forests

U.S. Forest Service researchers and partners published new findings on how leaf-eating insects affect forest ecosystems worldwide.

The study took place in 40 forests including ʻŌhiʻa-dominated native forests on both the Big Island and Kaua‘i. Researchers analyzed leaf litter and green leaves for carbon, nitrogen, phosphorus and silica concentrations.

“Because of things like Rapid ʻŌhiʻa Death, but also issues like invasive species, understanding the impacts of herbivory [leaf-eating insects] on our most important native tree takes on greater significance,” said Bernice Hwang, the paper’s lead author and former U.S. Forest Service technician.

According to the study, published in Nature Communications Journal, the findings provide an improved understanding of the intricate relationship between herbivorous insects and forest ecosystems.

Hwang, along with fellow researchers found that a warming climate can affect how plants and herbivores interact. According to the study, changes in those relationships have important consequences for carbon and nutrient cycling in broadleaved forests on a global scale.

Researchers don’t fully understand how changes in leaf-eating (herbivory) rates by insects affect overall nutrient cycles in ecosystems or how climate shifts might change these dynamics. Researching the interactions between soil, plants and insect herbivores can help improve models for predicting how herbivores affect forest structure and function.

“We also found that concentrations of carbon and nutrients in leaves significantly increased with temperature globally,” Hwang said. “Put together, temperature shifts and insect herbivory can have profound effects on nutrient-limited forests.

“Understanding these interactions is crucial for improving biogeochemical models and predicting the effects of climate change on forest ecosystems. The study underscores the importance of considering insect herbivory in ecological research and forest management practices.”

Some nutrient sources, Hwang added, are well-known, such as particles from the air, minerals breaking down in rocks, and nitrogen fixed by certain organisms. However, other sources, like nutrient deposits from animal waste and decomposing bodies, are less understood.

“Plants need nutrients like nitrogen and phosphorus to grow, and their availability limits plant growth,” Hwang said. “To predict how forests will store carbon in the future and to make good climate policies, we need to understand what controls the availability of these nutrients.”

The researchers hope this new knowledge can contribute to a better understanding of forest ecosystems and inform efforts to conserve them.

“I believe this analysis will be a benchmark to compare against for its field,” said Nels Johnson of the Pacific Southwest Research Station.