Role of hardwood in forming habitat for southern California steelhead

TitleRole of hardwood in forming habitat for southern California steelhead
Publication TypeReport
Year of Publication2008
AuthorsThompson, L. C., Voss J. L., Larsen R. E., Tietje W. D., Cooper R. A., & Moyle P. B.
Series TitleProceedings of the sixth California oak symposium: today's challenges, tomorrow's opportunities. USDA Forest Service General Technical Report PSW-GTR-217
Date Published10/2008
InstitutionU.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station
KeywordsFish habitat, hardwood, large woody debris, Oncorhynchus mykiss, pools, rainbow trout, Salinas River, steelhead
AbstractLarge wood (LW) is known to be very important to fish habitat in conifer-dominated streams of the Pacific Northwest, but has not been well studied in hardwood-dominated streams of the central California coast. In July and August 2006, we studied the occurrence and function of hardwood LW in relation to stream habitat and threatened steelhead (Oncorhynchus mykiss) distribution in the hardwood-dominated Upper Salinas River watershed in central-coastal California. We sampled 15 sites located on four tributaries and on the main stem of the Salinas River. At each site, we measured the volume of fallen dead LW (logs, root wads), standing trees, and not-standing live wood (exposed roots, living fallen trees) within the bankfull width. Fish density and length were estimated by a snorkel survey. Willow (Salix spp.), oak (Quercus spp.), California sycamore (Platanus racemosa), and Fremont cottonwood (Populus fremontii) dominated the sites. Fallen dead LW volume within the bank full width averaged 47.6 m3 /ha (SD =58.2) across all sites. Total LW volume, including fallen dead, not-standing live wood, and standing live and dead trees averaged 222.0 m3 /ha (SD = 173.7). Fallen dead LW volumes on the central coast were almost 16 times less than conifer-dominated sites in the Pacific Northwest, but similar to volumes on private hardwood dominated north coast sites. At 13 sites at least half the pools were formed due to LW, or experienced some influence of LW. An average of 4.01 fish/m (SD = 3.08) were observed at 14 sites. Steelhead were observed at 9 sites, averaging 0.23 fish/m across 14 sites (SD = 0.35). Hardwood LW appears to be an important component of steelhead habitat in central-coastal California streams, due to its influence on pool formation.