Comparing leaf litter, Chapman evaluates the impacts of herbivory in different forest types.

This story first appeared in the SERC quarterly Newsletter Fall 2006

Small Bites Add Up

Many of us don't think much about the impacts of plant-eating insects on the world until aphids invade our gardens or the emerald ash borer threatens the health of a national forest. But recent studies by post doctoral fellow Samantha Chapman give us a reason to look further. In a paper published in the journal Oikos, Chapman and her colleagues showed that the effect herbivores have on the type of leaf litter on the forest floor can significantly influence nutrient availability. They also showed that the impacts are distinctly different between forest types.

The study revealed that the response of evergreens and deciduous trees to herbivores may have opposite effects on the availability of nutrients in leaf litter on the forest floor. Evergreens tend to drop their leaves as a defense mechanism when they're being munched on. So, in the presence of herbivores, leaves fall earlier than normal, before the plant has time to resorb (or "take back") nitrogen. Not only is there more leaf litter falling to the forest floor, but it is higher in nutrients, resulting in a pulse of nutrient availability.

In contrast, herbivory in deciduous forests does not often cause trees to drop their leaves, but causes them to produce compounds in their leaves that reduce the rate of decomposition, resulting in a slower release of nutrients.

"This work presents a new way of thinking about how herbivores can control processes much larger than themselves," Chapman said. The researchers suggest that more attention should be placed on the role of herbivores in nutrient cycling and that this information may help managers understand their forests better. Chapman is continuing to explore the dynamic role of herbivores in a project with Candy Feller looking at how crab herbivory impacts mangrove forests.

For more information, or to reach Dr. Chapman, please contact SERC science writer Kimbra Cutlip .