Riparian Review - Discussion Questions

Background information:

Riparian areas are the transition zones between aquatic and terrestrial systems. The plants in this zone depend on high water tables and flooding patterns associated with the aquatic systems. Riparian zones cover a very small area in a watershed, but are extremely important.

Riparian Zone Functions:

• Bank stability to resist erosion
• Habitat for a diverse community of plants and animals
• Canopy cover which provides shading
• Organic materials drop from canopy cover into waterbodies
• Soils soak up water from runoff and help mitigate flooding
• Healthy riparian areas protect the land from flooding, and provide storage for a sustained summer flow

For more information, see:

• The Riparian Zone section of the Utah Stream Team Manual which defines a riparian zone and discusses how it would change due to natural and human influences, why the riparian zone is important in an aquatic ecosystem, and how to measure and interpret the results. 
• For information on Utah’s wildlife, see the Utah Division of Wildlife Resources Data Center website

Discussion Questions:

1. How do the greenline measurements help us understand how well a stream bank resists erosion?

Fast moving water can cause banks to erode. The greenline is a measure of how well the plants along the water’s edge will help the banks resist erosion (bank stability). We  determine stability by calculating the proportion of different vegetation types. These are sedges and rushes, shrubs and trees, grasses, forbs, (a non-woody plant that is not a grass), and bare ground. Each vegetation type has a different ability to stabilize the banks due primarily to the depth and density of the roots, and whether they are annuals (die back after one year), or perennials (live through the winter). For example, sedges are perennials that have deep, thick root masses that cling to and stabilize soils, while many annuals have shallow or sparse roots that do not contribute to bank stability.

In the field, look at the vegetation in areas where serious erosion has occurred compared to areas with stable banks. Think about how different land uses affect vegetation and therefore bank stability.
       

2.  How does the canopy cover affect the physical properties of the stream itself?

Canopy cover provides shade and is important in keeping water temperatures low in small headwater streams. Many fish and other aquatic organisms are sensitive to high temperatures, and may disappear from streams that have lost their shade. 

The canopy of a stream also represents the leaves and debris that may fall directly into the stream. This external input of material is an important source of food and shelter for the fish and other organisms living in these small streams. The relative importance of canopy cover (both for shade and for input of organic material) decreases as a river gets increasingly larger.

3.  How do humans affect the health of the riparian zone? 

The riparian zone is a very small area compared to the entire land area of a watershed, and humans can have a serious impact on this important ecosystem through different types of activities. 
• Clearing: Riparian areas are often cleared for agriculture, logging, or housing and other development. This can lead to destabilized banks, heavy erosion, and loss of stream and riparian functions.

• Introduced species: Many riparian areas are affected throughout the world by introduced species, which take over the riparian area and radically change the habitat. Species such as russian olive, tamarisk, and purple loosestrife may form “monocultures,” replacing native plants and resulting in a serious loss of plant and animal diversity and a loss in other riparian functions such as storing and filtering wastes.

• Grazing: While grazing by cattle and other livestock has been shown to be compatible with healthy riparian areas, the type of grazing is extremely important. Most riparian areas can handle short term, “intensive” grazing, with sufficient recovery time.  Continuous grazing in a riparian area can limit the plants’  abilities to recover and may ultimately lead to loss of vegetation or a change in species.

• Recreation: Recreationalists flock to riparian areas, but may “love them to death.” Trampling, multiple trails, wood removal for campfires, and littering all can impair riparian areas.

4.  Why would a stream area be a good habitat for wildlife?

Water is a critical need for all animals, so streams provide important access.The diversity of plant species (from small annuals to dense sedges to tall trees) provides food and shelter for a wide diversity of animals, ranging from insects to birds to mammals.  One function of riparian areas that people sometimes neglect is their use as a “corridor” for wildlife, providing connecting routes across otherwise dry or uninhabitable landscapes. These corridors are important not only for migration, but also for connecting  different breeding populations.