River Continuum

The River Continuum Concept (Vannote et al. 1980) has become the dominant concept of how stream ecosystems vary from headwaters downstream to large rivers. The Andrews Forest was one of four primary sites contributing to this pioneering ecosystem paradigm in the late 1970s and early 1980s. The basic idea is that aquatic communities and ecological processes of the stream ecosystem change predictably along the downstream gradient of increasing channel dimensions and canopy opening over the stream, such as:

• In forested landscapes, the relative contribution of forest litter to the energy base decreases and aquatic primary production increases in the downstream direction. Thus, the energy base of the stream ecosystem shifts from forest litter in shaded headwater streams to increasing influence of in-stream primary production in more open downstream reaches (the P/R ratio (production:respiration) increases in the downstream direction).
• The relative abundance of functional feeding groups of organisms follows this shift in food resources. Invertebrates that can shred forest litter dominate in headwater streams, and those that scrape algae and diatoms from rocks are more common in downstream reaches that receive more light.
• The density of large wood decreases downstream and its geomorphic and habitat functions shift.

The ideas now known as the River Continuum Concept (RCC; see RiverContinuumConcept.tif) began to be formalized during research associated with the International Biological Program (IBP) (1964-1974) at the Andrews Forest and other sites. This early cross-site program encouraged exchange of ideas among stream ecologists; these collaborations continued through National Science Foundation grants and the Long Term Ecological Research (LTER) program (1980-present). Early stream research often focused on instream dynamics at a single location. The Andrews scientists were leaders in thinking about differences in processes among streams of increasing size and throughout stream networks. While the River Continuum Concept is typically viewed as a global stream ecosystem theory, it can be applied to forested landscapes to depict forest-stream interactions with widening canopy opening over the stream and shifting geomorphology in the downstream direction, a direct result of the unique interdisciplinary collaborations at the Andrews Forest that included geomorphologists, forest ecologists and aquatic ecologists.

Recognition of the importance of these linkages between streamside forests and instream communities has resulted in creation and protection of riparian buffers as Best Management Practices in many regions and parts of the world. In the forests of the Pacific Northwest, researchers help translate the ideas from the River Continuum Concept into forest management plans. Forest management strategies began to include recognition of the importance of riparian buffers as source of valuable materials (wood, leaves and needles) for instream communities, as filters influencing delivery of nutrients and sediment to streams, and as shade controlling stream temperatures. The role of fallen trees as stable habitat for biota and major influences of geomorphic processes has become prominent in management of streams throughout the world.