Studies show positive impacts of Large Wood Addition projects on trout habitat, stream ecology

​Riverkeeper note: The following column and podcast rehash was written by Northern Tier Regional Director Emily Shosh. You can contact her directly at [email protected]

Over time, streams naturally carve their own path as water runs over the lay of the land, interacting with vegetation and different substrates and sediments along the way. This process also creates different parts of a stream, all of which play a role in water quality, trout habitat and overall stream health. 

In Pennsylvania, this system has been disrupted over the last two centuries primarily through human activities including excessive logging and the loss of forest age/structure diversity, the overall loss of riparian vegetation, inadequate and/or undersized culverts and stream crossings and other development within the stream corridor.

One solution to this issue is Large Wood Addition (LWA) projects, also referred to as Large Woody Debris, Large Woody Material and Strategic Wood Additions.

These projects involve felling trees into streams in a way that mimics the natural conditions of a forested stream under normal conditions. The debris thus creates scour pools, cover for fish and other aquatic life, and reconnects the stream to the floodplain.

These habitat projects work with the existing stream system and are highly regarded as one of the most effective methods for trout habitat improvement according to Stream Restoration Specialist Phil Thomas, of Trout Unlimited.

Thomas, originally from Hollsopple, attended Waynesburg University where he “majored in playing football and minored in biology.” His bachelor’s degree led him to seek outdoor work, which began with the PA Fish and Boat Commission as a seasonal technician in the agency's Habitat Management division based out of Bellefonte. This eventually led to a full-time position spanning nine years within the same division. 

Thomas moved into a similar position with National Trout Unlimited in 2015.

In the summer months, Thomas is in the field constructing a combination of habitat and stabilization projects. Stabilization projects “are more ‘traditional’, involving rock and log structures that stabilize banks and provide additional habitat,” he said.

​These project types are common across the state and were first introduced by the Pennsylvania Fish and Boat Commission back in the 1950s and 60s.

Check out the full interview with Trout Unlimited Stream Restoration Specialist Phil Thomas in our most recent episode of the Middle Susquehanna Riverkeeper Podcast:

Kathleen Lavelle (wearing an electrofishing backpack unit), Trout Unlimited Field Coordinator for the Northeast Coldwater Habitat Program, leads her crew in Potter County in Spring of 2024. Her field data was used to monitor LWA projects.

“Primarily, our focus is on wild trout waters, where we are always looking to create more habitat," Thomas said. "There’s also an emphasis in funding on erosion in the Chesapeake Bay, which is where stabilization projects come in, helping to control erosion."

Thomas also organizes and assists aquatic organism passage work, where undersized stream crossings are replaced with larger culverts or bridges that do not limit fish movement. Adequate passage through stream crossings is important during spawning, provides more feeding opportunities, and allows fish passage during seasonal changes in water levels. Undersized crossings also lead to excessive erosion and damage to infrastructure.

The other major project type Thomas and his team oversee has been called a number of different titles.

“Large woody debris ... strategic woody additions ... basically meaning we add trees to the stream,” he said.

Trout Unlimited typically handles the design, permitting and construction oversight of the LWA projects, depending on the site location.

The placement of these projects is data driven, based on extensive literature and peer-reviewed papers on benefits of wood in streams.

"Some of our Trout Unlimited field offices in Vermont have seen a 150 percent increase in brook trout biomass through large wood additions,” Thomas explained.

In Pennsylvania, Trout Unlimited currently has one year’s worth of post-construction data, and initial findings are very promising.

“All matrices used in the study had a significant increase in trout biomass, although we can’t draw any major conclusions from one year’s worth of data,” he said, pointing out that part of this absence of data specific to PA is due to permitting, which had not allowed for such projects to be done until about six or seven years ago. ​

​Allison Lutz, Science Coordinator for PATU’s Northeast Coldwater Habitat Program, provided some results from an initial study of sites pre- and post-LWA. 

Post-LWA, an increase in both brown and native brook trout size classes and biomass were reported across surveyed locations, as well as a notable increase in suitable habitat for all life stages of brook and brown trout based on the substrate and cover at the sites. For a full write up of the report, email Allison at [email protected]

Trout Unlimited and several other agencies are currently working to generate more PA data to further validate the need for LWA work. Thomas is optimistic that the data will show LWA will benefit our streams “just like it does everywhere else in the country.”

In terms of a focus area in PA for projects, Thomas cited the national Trout Unlimited’s Priority Waters initiative as a guiding voice in project prioritization. These areas in Pennsylvania include portions of the Allegheny River, West Branch of the Susquehanna, Laurel Highlands and the Delaware River.

Specifically, Thomas has mostly been active in the Kettle Creek watershed within the West Branch of the Susquehanna. Recent funding has also expanded some project areas to the Allegheny National Forest and the Pine Creek valley.

Two standout projects come to mind for Thomas, one being the Beaverdam Run Branch, a tributary to Kettle Creek in northern Clinton County. This happened to be, in his opinion, the very first true restoration project he accomplished.

"We went from the mouth of that tributary to where we ran out of water and we treated it with large wood and we stabilized some eroded banks," he said. "All together, it was like four to five miles of stream that we improved over a couple of years. At that point, I had been doing this (type of) work for like 15 years, but it was the first time where we had restored an entire watershed."

Thomas feels the Beaverdam Run Branch project and other similar work is real restoration given its more contiguous project design.

Another stream close to Thomas’s heart is Gifford Run, a tributary to Mosquito Creek in Clearfield County. Over three miles have so far been restored through large wood placement, but more is planned in the coming years.

Because it was a larger stream system, "this was the first time we could really get to see all the benefits first-hand," Thomas said. "Most of what we’re doing is in first-order streams where it takes time to see the habitat bounce back, but in Gifford it took only a few months to see the trout."

These projects, while rewarding, do not come without challenges. One being the planning and logistics of bringing in supplies and equipment to remote areas while being mindful of keeping impacts at a minimum and keeping workers safe. Thomas takes this responsibility seriously.

Another common hurdle are naysayers of the work.

"The public's perception of these projects has generally been pretty poor. They think it’s a bunch of chainsaw-happy guys in the stream," Thomas said. While he acknowledges the novelty of the projects might seem alarming, there is also general misinformation being shared by word of mouth.

"Firstly, these projects are carefully planned and permitted by trained professionals. Secondly, the goal of these projects is to benefit fish - creating complex woody material for young of the year trout, providing overhead cover for larger adult fish, increasing pool habitat upstream and downstream of the site and more. We’re doing it for the fish."

Not just the fish benefit, but the entire watershed. Large wood structures retain leaf litter - the cornerstone of the aquatic food chain. More leaf litter means more insects for trout and other aquatic organisms. The leaf litter also helps capture sediments and gravel, depositing it to the floodplain and benefitting vegetation within the riparian zone. 

This deposition not only benefits plants, but reconnects the stream to the wider floodplain, which helps slow water down to reduce excessive erosion during high water events. Reconnection with the floodplain also improves infiltration of water into the ground, meaning the ground water tables are higher, which is vital to aquatic life in drought season. Ground water is colder and gradually recharges the stream with cooler water in summer.

"There's a reason people have been digging root cellars for centuries, this is the same idea. When that cold water flows back into those slow drought flows, it prevents stress on fish," Thomas said.

He admitted that LWA can be a whole-watershed approach to restoration. Even wildlife see some interactions with the project sites. The logs may serve as a creek crossing for many animals, deer bed down under felled trees, grouse use the logs as their drumming stage and more. 

One of the simplest yet most effective ways to help with this work is to do research and share sound data to help inform others about the goals of large woody debris projects, Thomas suggested.

"We’re not trying to make streams unfishable, we’re trying to sustain these streams for the future by mimicking their natural succession," Thomas said.

Additionally, agencies or volunteers can reach out to Thomas directly to get involved with projects, or for technical assistance with completing their own projects. He can be reached at [email protected].

Read more here for a comprehensive list of LWD happening across the state through multiple agencies.