Headwater Streams
10,000 Years Institute is studying the link between riparian forest structure and the stability of instream wood and sediments.
Functional, complete riparian forests provide critical ecological services throughout the stream network. Even in steep headwaters, a mature riparian forest provides shade, stream bed and bank stability, cover, and energy sources for aquatic food webs. Instream wood derived from riparian forests reduces local stream gradients, provides instream cover and habitat structure, and functions to retain coarse sediment crucial for fish habitat (Figure 1). Destabilization of steep stream beds can result from intensive land use such as logging in headwater riparian forests. Destabilization results in massive sediment movement over a short period of time, destroying complex habitats in steep areas and downstream (Figure 2).
Figure 1. A natural distribution of wood and sediment in Snider Creek, tributary to the Hoh River, Olympic National Park, WA. Wood has several important ecological functions in the stream, including provision of a source of organic material for food, shelter for fish and aquatic macroinvertebrates, sediment retention, and increasing habitat heterogeneity.
Figure 2. Site of a recent debris flow on Virginia Falls in the Hoh River Basin on the Olympic Peninsula, WA. The bare creek bed shows how the debris flow eliminated vegetation and stream substrate.
This research will provide a basis for understanding whether current forest practice rules are sufficient and appropriate to protect the integrity of headwater streams and the river network to which they are connected. Data collection, analysis and reporting are in progress; see our 2003 Poster Presentation (pdf format - 5.2MB) for a summary of results to date.