• Rocky Mountain Research Station
• 240 West Prospect
• Fort Collins, CO 80526
• (970) 498-1100

Spatial Variation in Coarse Wood in Streams and Riparian Zones

To address these issues, we censused instream coarse wood (> 2 m long and > 10 cm minimum diameter) and sampled riparian coarse wood and channel characteristics in and along very long (1.0-8.0 km) segments of 13 streams in western Montana. These streams lacked evidence of land management, such as roads, logging areas, or mining sites, and represented controls that could be compared to managed basins.

Surprisingly, the average dimensions of instream coarse wood showed little relation to pieces found in the riparian zone, which was probably due to the breakage and abrasion of instream pieces caused by high flows. Moreover, the abundance of coarse wood was only weakly related between streams and their adjacent riparian zones, which we attributed to the transport of pieces by the stream and by the more-rapid decay of pieces laying in the riparian zone. This demonstrates that estimates of coarse wood loads in riparian zones cannot be substituted for instream surveys, and that very different processes are responsible for the patterns of coarse wood loading in each location.

Instream coarse wood also displayed highly variable spatial patterns. Counts or volumes of coarse wood in adjacent 50-m reaches were often uncorrelated and highly variable. Many times reaches with average or above-average wood loads were next to reaches that contained no wood, and characteristics of the stream channel such as gradient did not help explain this relation. As a consequence, the length of stream that one would need to survey in order to estimate coarse wood abundance within 25% of the true value was over 1 km. This contrasts with the common practice of measuring coarse wood over reaches used to measure geomorphological characteristics, which for these streams would have been about 200 m.

Results of this research will be critical to: 1) establishing defensible standards for coarse wood abundance in northern Rocky Mountain streams; 2) crafting statistically robust monitoring protocols for coarse wood; and 3) understanding the ecological relation between instream and riparian coarse wood through successional time.

More information can be found in:

Young, M. K., E. A. Mace, E. T. Ziegler, and E. K. Sutherland. 2006. Characterizing and contrasting instream and riparian coarse wood in western Montana basins. Forest Ecology and Management 226: 26-40. .