Logjams Benefit Wildlife So Much That Scientists Are Intentionally Placing Wood in Streams

Study finds it's not just fish that use wood pieces for shelter and passage.

Gray wolf in stream
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When a large chunk of wood sits in a stream, it offers benefits to the creatures around it. New research finds it’s not just fish, but other wildlife that take advantage of the wood too.

Researchers were curious how logjams and floating wood could have an impact on animals in the ecosystem.

“We were interested in this topic because as the importance of large wood in rivers is well recognized for salmon, we knew little about the implications for wildlife,” study author Ivan Arismendi, a scientist at Oregon State University, tells Treehugger.

“So we were wondering whether animals can also be benefited by these structures.”

In the past, land managers often removed large pieces of wood from water, thinking they could be harmful. People liked the aesthetic and benefits of a smooth, free-flowing stream.

“Historically, large wood was removed from rivers because of the perception of logjams as potential hazards during flooding events,” Arismendi says. “Also, large wood was considered a barrier for navigation and transportation. In some cases, logjams were considered places where debris accumulated.”

Then people realized there were benefits to the wood blockades. Beginning in the 1980s, millions of dollars are now spent each year to place large wood back in streams. The wood is important to create habitat for fish, for sediment deposits, and for stream discharge.

Unexpected Visitors

Knowing that fish use the wood, researchers wanted to see what other animals might take advantage of it. 

They set up 13 motion-triggered video cameras along Rock Creek, which is about 15 miles west of Corvallis, Oregon. They collected 1,921 videos between June 2020 and June 2021 that had at least one animal interaction.

The most common activities they observed included movement (in 68% of videos), rest (18%), and food handling or eating (9%). The researchers write that these observations suggest, “that large wood structures in streams act as lateral corridors connecting terrestrial habitats year-round for wildlife.”

They noted as many as 40 species including small mammals, medium and large carnivores, aquatic and terrestrial birds, and semi-aquatic mammals. There were more species and overall animal observations in summer and spring, with the fewest sightings in winter.

They also spotted many unexpected species including a golden eagle, which is rarely seen in the area. They also saw two mule deer trying to climb onto a log for safety during high waters, but they were swept away. And they observed a raccoon and deer mouse crossing a logjam with water covering the entire log.

“We were surprised by the many species actively using logjams and the multiple roles that these structures play for wildlife besides the obvious role as a bridge between river banks,” Arismendi says.

The findings were published in the journal Biodiversity and Conservation.

Studies Continue

Researchers are going to continue the study this summer in H.J. Andrews Experimental Forest in Oregon’s Cascade Mountains with 30 additional motion-triggered cameras.

They hope the findings will be useful to land managers as they consider the value of projects that place wood in running water.

“Large wood in rivers can connect habitats that were potentially disconnected in the past,” Arismendi says. “It can increase the size of habitats for wildlife, serve as a place to search and handle food or act as potential refugia.”

View Article Sources
  1. study author Ivan Arismendi, a scientist at Oregon State University

  2. "Oregon State Research Highlights Importance of Large Wood in Streams for Land-Based Animals." Oregon State University.

  3. Trevarrow, Ezmie, and Ivan Arismendi. "The Role of Large Wood in Streams as Ecological Corridors for Wildlife Biodiversity." Biodiversity and Conservation, 2022, doi:10.1007/s10531-022-02437-2