Finding Balance

Forests and streams are separate but linked ecosystems, existing side by side, with energy and nutrients crossing their porous borders and flowing back and forth between them. For example, leaves fall from trees, enter streams, decay and feed aquatic insects. Those insects emerge from the waters and are eaten by birds and bats.

An international team led by Penn State researchers has found that these ecosystems appear to keep the energy exchanges in balance — a finding that surprised the scientists.

The study, published in Ecology Letters, sheds new light on the relationship between forests and streams. The researchers analyzed data from 149 studies of coupled forest-stream ecosystems around the world and found that aquatic and terrestrial organisms consume the same amount of energy as those in the opposite ecosystem.

"This was an interesting and unexpected result because we know that there's way more energy flowing into streams in the form of leaves that fall from trees than what comes out in the form of emergent aquatic insects," said the study's lead author, Daniel Allen, assistant professor of aquatic ecology. "But the quality of the resources is vastly different because the aquatic insects that emerge from streams are very nutritious."

—Jeff Mulhollem