Disrupting the flow of driftwood affects marine ecosystems

Throughout history, rivers have transported a large amount of driftwood to the oceans. However, humans all over the globe are increasingly interfering with this process. New research led by Colorado State University (CSU) has found that disrupting the flow of driftwood from rivers to oceans can have a significant impact on marine ecosystems.

“Dead trees, known as large wood in rivers or driftwood in oceans, have come to be more appreciated since pioneering research in old-growth forests revealed the role of standing and downed dead wood in providing nutrients and habitats to a wide array of organisms,” wrote the study authors.

Driftwood also plays a crucial role when it reaches both freshwater ecosystems, such as those in rivers or lakes, and marine ecosystems. In the open ocean, driftwood provides vital habitat and food sources for a large variety of organisms, including mollusks, fungi, crustaceans, and microbial communities.

“When driftwood sinks, it’s like a sunken coral reef,” said study lead author Ellen Wohl, a fluvial geomorphologist at CSU. “Living creatures, mostly invertebrates, clams and crustaceans use that wood as a refuge.” 

During the past few centuries, human activities have significantly reduced wood supply to the oceans by altering each component of production, recruitment, or transport. “We as humans have been altering the wood cascade and interrupting it for more than a century,” said Wohl.

Driftwood is often removed in some coastal areas, such as tourist beaches in the Mediterranean, disregarding its crucial role for a variety of animals and plants, as well as for the movement of sand.

“Small scale human impacts, such as removing wood from a river, draining a floodplain and logging a hillslope, affect the entire river corridor at a much broader scale,” said study co-author Emily Iskin, a doctoral student in the Department of Geosciences in the Warner College of Natural Resources at CSU. “Everything is connected. Logjams in a river are not only beneficial to that local ecosystem, but also provide benefits downstream all the way to the open ocean.”

Professor Wohl hopes that these findings will increase efforts to measure wood flux to the oceans from the remaining relatively undammed rivers such as the Yukon and the Mackenzie in North America, or the Amazon and the Congo in the tropics, and help reduce humans’ interaction with these essential natural processes.

The study is published in the journal Science Advances.

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By Andrei Ionescu, Earth.com Staff Writer