Coastal plain streams don’t always have swirling eddies or meandering bends. “They can look more like drainage ditches than natural streams,” says USDA Forest Service technician Ken Sterling. Agriculture, flood abatement, and residential development have all contributed to stream straightening in this region.
The result? Streams incise and downcut, like a canyon. “These streams are wide, straight, and shallow. They have level, sandy bottoms and uniform depths. “Wood is swept out of the stream every time there is a good rain. Without wood, fish lack places to shelter and find food,” adds Sterling.
Wood offers fish a refuge from swift currents, cover from predators, and a source of invertebrate prey. Fish in lowland, coastal plain streams are more dependent on wood because these environments lack the rocky substrate and cover found in upland streams.
And a large percentage, more than one-quarter, of southeastern fishes are imperiled.
In one experiment, they introduced small wood to several stream reaches and measured the impacts on fish community abundance and diversity. Their study results were published in Southeastern Naturalist.
Sterling and Warren selected a degraded section of the Little Tallahatchie River system in northcentral Mississippi and installed bundles of small wood – pieces that were less than four inches in diameter and four feet in length. The small wood bundles were made from freshly cut shrubs and fastened to rebar driven into the stream bed.
In some sections, the researchers installed wood bundles in patches, leaving gap openings in between. In other sections, they placed additional bundles, creating a denser structure and filling the gaps. Some sections were left untreated to represent existing stream conditions.
Every few months, from July 2009 to May 2013, the researchers sampled the entire area of each treatment. They identified, counted, and released fishes.
They had to re-attach some of the wood bundles during the study. The degraded stream often experienced flashy flows. Flooding during these events would pull the bundles loose and move them downstream.
“We saw greater species richness in the reaches with introduced small wood,” says Sterling. The scientists found a greater abundance of fish in both the dense and patchy treatments, but they didn’t observe differences between the two. They counted fewer fish species, across all families, in the areas without any introduced wood.
Darters (Percidae) and catfishes (Ictaluridae) – including species like the brindled madtom (Noturus miurus) and dusky darter (Percina sciera) — showed the greatest positive response to the woody treatments.
A few species, including the longear sunfish (Lepomis megalotis) and Yazoo shiner (Notropis rafinesquei), weren’t more abundant where the woody treatments were located. “Design is important – the amount and placement of wood could affect or benefit different fish species, because they use it for different reasons,” says Sterling.
The researchers plan to repeat the study in a smaller stream with lower energy, where flows would be less likely to move or disturb the small wood bundles. They plan to study the bigger-picture ecology of the streams and examine impacts on invertebrates – such as crayfish populations.
“When you look at Coastal Plain stream restoration in the Southeast, you’re talking about wood – putting wood into streams. Installing large wood is expensive because of the time and equipment required,” notes Sterling. “With this project, we wanted to develop methods for installing small wood to reduce costs and demonstrate that small wood can be an effective restoration approach.”
For more information, email Ken Sterling at firstname.lastname@example.org.