The importance of riparian vegetation


Do you remember the moment when you caught your first fish? Perhaps you were standing knee deep in a river, but more likely you were standing on the bank, your feet rubbing against the short grass, your toes comfortably rubbing the stubby vegetation. Well, for scientists studying river banks, that stubby vegetation is called “riparian.”

Some readers may have heard the term riparian before — either around town, in the paper, or in some context referring to local ecological research on the many beautiful streams and rivers that cross the southern Appalachians. Riparian is simply a term that means next to rivers or streams, so references to “riparian vegetation,” “riparian setbacks” or “riparian species” simply mean “plants next to the river,” “not allowing development next to the river,” or “species that live in the area next to the river.”

The riparian area is very important for a number of reasons, and thus has been the focus for many Coweeta LTER researchers. The plants that naturally inhabit this unique habitat perform several important functions: they filter sediment from runoff flowing from higher in the catchment; they assist in the removal of excess nitrogen from the streams; they hold sediment on the banks with their roots, preventing it from washing into the stream. These plants also shade the water, both keeping it cool and occasionally dropping in leaves and branches that river creatures find nutritious and sheltering. Finally, riparian plants also provide valuable habitat for species that need both terrestrial (i.e earthly) and aquatic habitats, like salamanders.

The removal of woody vegetation from riparian zones is a relatively new development. Humans settled along floodplains and near the water and removed riparian vegetation for agriculture, building materials, and food. Although this was convenient for people, it created ecological problems for fish, salamanders, and other living things that had evolved in these shaded waterways.

In the Southern Appalachians, removal of riparian vegetation has a significant negative impact on aquatic species. Removing riparian vegetation potentially opens the way for more sediment to enter the stream; coming either directly from the stream banks because there are no more roots to hold it in place anymore, or washing into the stream from further away on slopes in the catchment.

This sediment clouds the water, making it difficult for fish to find prey and mates, and it eventually sinks to the stream bottom. The sediment that reaches the stream bottom gradually covers the many different-sized rocks and cobbles that used to provide safe nesting sites and places to hide for small fish. The streambed becomes simpler, and warmer. What was once a stream with many different types of habitat to accommodate many different types of fish, many of which require different types of habitat during different parts of their life cycles, becomes more homogenous and appealing for sometimes problematic species that did not evolve in the rocky and clear mountain streams.

In addition to studying these effects, Coweeta LTER researchers are attempting to determine how much riparian or upslope vegetation can be lost before a stream starts to suffer.

By studying the amounts and types of fish living in streams that have lost differing amounts of riparian vegetation, researchers have found that removing trees from lengths longer than 1 km (0.6 miles) can cause serious problems for fish and stream health, even if the rest of the area around the stream is mostly forested.

They also found that the length of the deforested riparian zone had a stronger effect on fish and stream health than the width of the deforested riparian zone, probably meaning that the most important job of riparian trees are shading and protecting the banks of the river from washing away. So the next time you go fishing, remember riparian — and reel in the big one.

In addition to avoiding clearing trees and vegetation from riparian zones on private property, local residents can help keep rivers healthy by fencing out livestock. Local residents and tourists alike can also help by trying to disturb banks as little as possible when fishing and recreating in the many beautiful local rivers and streams.

 

This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at cwtlistn@uga.edu or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.

 

Original Citation: The Coweeta Listening Project. Franklin Press. Column on "Science, Public Policy, Community." Page B4. Feb 3, 2012.