An Assessment of Riparian Vegetation in a Human-Influenced Landscape
Given that humans historically have heavily used rivers and the lands along them for agriculture, transportation and other activities, how does human impact currently affect riparian ecosystems in a rural region? Students will address this question through several activities. From sites spanning a range of historical human influence, students will collect and analyze field data, including structure, composition and distribution of vegetation, soil pH and moisture, and light availability. Human use, both modern and historical, will also be assessed for each site. Using this collection of data, students will interpret and contrast ecosystem function across sites, and then place in the context of human land use. Students then investigate whether existing riparian laws provide adequate protection for ecosystem function.
The "big ideas" for this activity are:
- Structure and function of ecosystems are linked. Specifically, large trees as structures in riparian ecosystems support river ecosystem function by shading rivers to cool water temperatures, and providing a source of large woody debris to create complex riverine habitat.
- Human activities can impair ecosystem function. In this project, human impacts on riparian vegetation are analyzed both quantitatively and qualitatively. Impaired riparian ecosystems are linked with impaired riverine ecosystems through group discussion in the field and student research following the field trip.
- Discern riparian from upland ecosystems.
- Locate local rivers and riparian ecosystems.
- Measure ecosystem attributes using ecological field equipment.
- Identify native tree and shrub species, as well as common invasive plant species.
- Collect and analyze ecological data.
- Assess human impacts on riparian ecosystem structure and function.
- Research state laws regulating activities in riparian ecosystems and assess their effectiveness.
Context for Use
Timeframe: This activity spans two (2 hour) lecture sessions followed by an eight hour field trip. It can be taught as the first module or a later one within a series, or could be a stand-alone unit. The only time restrictions are planning for appropriate conditions for field work.
Description and Teaching Materials
- Lectures include background on riparian ecology, human use of riparian areas, and laws regulating those activities. During one of those sessions and on the field trip, students will learn to identify common tree and shrub species of riparian areas.
- Field trip consists of qualitative and quantitative stops, both including pristine and degraded riparian ecosystems within the Chehalis River Basin.
- Data will be collected at two or more sites, including: trees by species, diameter, density and maximum height; shrub density; canopy cover; understory light levels; percentage of cover of natives versus. Invasive species, temperature and relative humidity.
- Qualitative assessments are made at all sites of vegetation and land use by humans.
- Data collected in the field are ideally shared in the field so that students can take home the summary data to write their reports. Alternatively, data may be posted on a web site for later access.
- Students independently research state laws regulating activities in riparian ecosystems and assess their effectiveness at protecting riparian structure and function.
Teaching Notes and Tips
The data collected for this project can be varied according to equipment, time and expertise available. Additional data that can tie in directly with riparian ecosystem function include soil moisture, pH, bulk density, texture and fertility; water quality such as pH, dissolved oxygen, and nitrates; herbivory estimates; and litterfall.
- data sheets collected in the field,
- graphs and tables of data,
- a written report of their riparian assessment, and
- a written analysis of a state law regulating activities in riparian ecosystems.
Informal assessmentsDuring the activity, student learning can be informally assessed during the field trip in several ways. The instructor should observe data collection to validate that methods are followed appropriately, and that species are identified properly. At each site, the instructor should lead a group discussion to solicit ideas from each student on riparian health and site history.
References and Resources
Washington State laws can be found on the web. Search for river or riparian for those most relevant:
Book chapter: Riparian Management in the 21st Century. Gregory, Stanley V. 1997. In Creating a Forestry for the 21st Century: The Science of Ecosystem Management. Ed. Kathryn A. Kohm, Jerry F. Franklin. Island Press.
Oregon Trout has some background resources for educators: