By Natalie Kramer Anderson
I study driftwood in rivers. I have traveled to rivers and creeks in Canada, the United States, Colombia, Chile, Honduras, Mexico, Peru, Italy, and Switzerland noting the abundance, or lack thereof, of streamside wood. For the past few years, partly funded by the National Geographic Committee for Research and Exploration, I have intensively studied the transport and impacts of large amounts of driftwood on big rivers and lakes in Northern Canada, and I just published a paper on what we found.
When I speak to people about my research they always ask, “Why driftwood?” For many it seems an odd thing to study because driftwood (in rivers) isn’t something that most people notice. In fact, several perception studies have shown that throughout the world most people actually relate dead wood along stream channels with the need to restore or clean up the river channel.
In reality, driftwood is a very important component of all natural waterscapes.
Driftwood alters the physical form of banks and shorelines, creating patchwork landscapes that support higher levels of biodiversity and ecosystem functioning than in the absence of wood.
Driftwood is an important line of defense along coastal beaches against erosion by waves, which is especially important as sea levels rise.
World-wide dispersal of organisms is often attributed to rafting on wood across oceans, and sunken wood in the deep ocean supports webs of life that would otherwise not exist in such an extreme environment with no light source to fuel plant growth.
There is a striking difference in amount of driftwood and habitat quality when comparing river corridors with and without intensive development, such as dams and deforestation for agriculture.
In Colombia, South America, driftwood lines the banks along rivers, such as the Samaná, that flow through jungles left intact during guerilla warfare and is absent in nearby deforested and heavily grazed catchments. The free-flowing Rio Marañón in Peru is located in the high Andes. Despite draining a canyon with sparse vegetation, large driftwood piles accumulate on top of mid-stream gravel bars in wider and flatter sections. Both the Rio Samaná and Rio Marañón have proposed large hydropower projects that will be built within the next decade.
European rivers generally lack wood due to a long history of streamside cultivation, but many rivers are currently undergoing re-forestation due to de-settlement during and after WWII. River managers are noticing an increase downed wood, and researchers are studying the benefits to the ecology and the problems with deposition against bridge piers and other in stream structures.
In the Mississippi basin, United States, historical accounts from European settlers describe stream wood accumulations that were so massively impressive in size that it verges on unfathomable to those of us who visit the river today. One observer described a river wide raft on the Red River in Louisiana circa 1928 as:
“…not standing still, but is gradually progressing upwards, like a destroying angel, spreading desolation over a most lovely country” (D. Joseph Paxton, 1828)
Of course, the spreading desolation point is a matter of cultural opinion.
In rivers draining the mostly undammed Mackenzie basin in Canada, river rafts and landscape features associated with wood are abundant and reflect conditions that were likely more common world-wide for the last 10,000 years up to about 200 years ago. The impacts of large amounts of driftwood on waterscapes—ecological and physical—is absolutely stunning both in scale and in aesthetics which is best conveyed through imagery. Here are a few of my favorite photos from my latest field excursions to the Slave River and Great Slave Lake in the Northwest Territories, Canada.
As the world’s last free flowing rivers are rapidly dammed for hydropower, I wonder: how will diminishing transport of driftwood impact the biodiversity of river corridors and marine environments? How much more at risk are wood-depleted coastlines from erosion associated with sea level rise and extreme weather? And, what impact will wood depletion have on freshwater and marine fisheries?
My work has been funded by the National Geographic Committee for Research and Exploration, the Geological Society of America, Chuck Blyth, and the Warner College of Natural Resources, Colorado State University.
Suddenly hooked on driftwood? We’ve got you covered: Additional Reading.