Gales Creek Large Woody Debris Inventory Report

Historically, Gales Creek likely would have been in a forested watershed with opportunities to receive LWD input from the upper watershed and the recruitment zone throughout its length. In autumn of 2005, we observed very few pieces of LWD or debris jams within the surveyed portions of the creek. While the recruitment zones of these reaches possessed greater numbers of wood than the channel, the likelihood of the wood to reach the creek is greatly diminished due to the primarily agricultural land use in the area. We found an average of 0.08 pieces of wood per ft and 0.001 debris jams per foot on our surveys. While direct comparisons with historic LWD abundance in rivers in the Pacific Northwest are difficult to make, Sedell and Froggatt report that in the Willamette basin between 1879 and 1950, an average of 1.8 snags per foot were removed from rivers (1984). Each snag may have had one or more pieces of LWD within it, but even if each snag was only one piece of wood, the historic numbers across the Willamette valley are two orders of magnitude higher than those found in Gales Creek during these surveys. Collins et al. (2002) cite the description of Puget Lowland rivers by an early army general:

…the channels are strewn with immense trunks, often two hundred feet long, with roots, tops, and all …[forming] jams, which frequently block the channels altogether [Major Hiram Chittenden, 1907].

This reveals the great occurrence of LWD and corresponding root wads and branches in the pre-settled Pacific Northwest. In our surveys we found only one root wad, defined as meeting the minimum criteria for diameter (1-2 ft) but less than 6 ft long. When root wads were part of pieces of LWD longer than 6 ft, they were not recorded as such.

Large woody debris counted within the Gales Creek survey reaches were primarily in the 1-2 ft diameter range. Compared with historic records of tree sizes within Pacific Northwest, these are small pieces of wood for a stream like Gales Creek. For Puget Lowland rivers, Collins et al. (2002) report information from the U. S. War Department records showing that between 1889 and 1909 the annual maximum diameter of wood in rivers ranged from 11.8 to 17.4 ft.

Temperatures within Gales Creek on our survey dates ranged from 10 to 15 °C. These are below the recently-published upper limit of the realized thermal niche for cutthroat trout, 16.2 °C (Huff et al. 2005). However, these numbers are the result of a single sampling, and temperature within the planned restoration reaches should be monitored throughout the restoration process. High temperatures have been previously cited for Gales Creek (Breuner 1998) and are linked to processes other than the occurrence of LWD within streams such as riparian vegetation and stream shading (Cederholm et al 1997).

The lack of wood within Gales Creek can likely be attributed to land use changes such as forestry and agriculture, as is noted in other systems of the Pacific Northwest (Bisson et al. 1987; Hicks et al. 1991, Bilby and Ward 1991; Collins et al. 2002). The relationship between habitat needs of salmonids and LWD in fresh water systems has been often described (Bustard and Narver 1975; House and Boehne 1986; Bisson et al 1987; Cederholm et al. 1997). Therefore when resource managers are tasked with mitigating habitat for dwindling salmonid stocks, installation of LWD pieces and jams is frequently employed.

Due to the small numbers of LWD and the lack of debris jams within Gales Creek, LWD structures could be constructed throughout to diversify habitats, supplement food supply and create refugia for salmonids. The TWRC has already proposed to place LWD structures in the surveyed reaches. The placement of instream structures on a small scale, such as proposed for Gales Creek, has been implicated as good technique for providing short-term improvements in habitats for certain species (Roni et al. 2001).

For example in the Alsea and Nestucca basins, Oregon, placement of wood in created alcoves and dammed pools increased the overwinter survival of cutthroat trout and steelhead salmon (Solazzi et al. 2000). Flossi et al. (1998) named log debris accumulations as the preferred summer habitat for young-of-year steelhead. These fish may overwinter along the margins of streams containing pieces of wood or boulders while root wads provide both summer and winter habitat for steelhead (Flossi et al. 1998).

To focus on improving habitat for steelhead in Gales Creek, the types of LWD structures appropriate for enhancement would be: root wads, single pieces of wood along the channel margins and LWD accumulations. Each can serve a separate purpose. For example, log weirs are usually employed across the channel; material collects on the upstream side of the weir and a scour pool eventually forms on the downstream side. The placement of debris jams can be directed to create scour pools, refugia and food resources within or along side channels. Side-channel LWD placement can create refugia for juvenile salmonids in the fragile early stages of their lives. Single pieces of wood may be within or above a stream’s bankfull width to create riffles, slow water eddies or pools, depending on the orientation of the piece. There are engineering concerns with each type of structure that should be adequately addressed by a restoration designer.

However, placement of single structures in sites scattered throughout a watershed may be viewed as part of a watershed-wide approach to promoting quality habitat (Cederholm et al. 1997). This technique is often successful as a temporary fix for threatened species (House and Boehne 1986; Cederholm et al. 1997; Roni et al. 2001) but will not persist if the reasons for the lack of woody structure in the stream are not addressed. It is best to view the placement of LWD within the identified reaches in Gales Creek as a temporary measure that may need maintenance and will promote long-term quality habitat only with corresponding watershed management. For long-term restoration, researchers suggest a watershed-wide program that includes protection of existing quality habitat in the watershed, conducting a watershed assessment to identify restoration needs and subsequently focusing on re-connecting habitats isolated by disturbance such as culverts or dikes (Roni et al. 2001). Management should also focus on accelerating the development of desired vegetation in the riparian zone (Cederholm et al. 1997). While the development of a mature conifer forest along Gales Creek will occur on a long (decades to a century) timescale, LWD placement as a restoration technique can promote desired habitat in the meantime.

Biological monitoring of restoration sites, especially over the long term, is not frequently conducted (Roni et al 2001; Koehler and Garono 2005). While we have a great deal of knowledge on coho salmon response to LWD placement, there are fewer studies revealing a response of steelhead, or cutthroat trout to such enhancement. Biological monitoring of such projects is necessary to promote further enhancement activities, increase the involvement of stakeholders and community support and to further restoration ecology. Biological monitoring may be more easily conducted if it is part of the restoration plan from the start of the project, and Gales Creek is a suitable place to conduct such monitoring.

Placement of LWD structures is a good way to begin mitigation for fish habitat loss. However, fish habitat must be addressed alongside watershed wide concerns such as connectivity, water quality, water use and sedimentation. Because the TRWC has already conducted a watershed assessment and enhancement plan and is building trust with local landowners, the Gales Creek watershed managers are well on the way to a more sustainable watershed.