Because riparian vegetation is the source of large woody debris in streams, trends in large woody debris and riparian vegetation are best considered as a group. Although there are few if any historic descriptions of large woody debris loading in Smith River, the abundance of large woody debris in stream channels was probably high at the beginning of European American settlement. Under conditions prior to European American settlement, the role of fire in riparian forests was probably minor. Catastrophic loss of riparian vegetation by fire was probably rare due to high moisture content and low slope position.

Since European American settlement, a trend toward lower quantities of large woody debris in many streams has occurred due to a combination of factors. Humans have directly removed woody debris from streams and in some cases added large wood to streams. Large woody debris, especially log jams, have been cleared from streams for various purposes including mining operations, misguided stream restoration, and possibly navigation improvement on the lower river. Other human activities have produced long-term effects by reducing the rates of recruitment of stream logs. Logging operations have influenced large wood in streams over both the long and short term. The immediate effect of early logging operations was probably an increase in large woody debris in streams. Following input of wood during logging, quantities of wood in streams probably decreased gradually because all large riparian conifers were removed during logging and were not available for recruitment into the stream (Bryant and Sedell 1995). Agriculture, road construction, and the 1955 and 1964 flood have also caused reductions in the size and/or quantity of conifers in riparian areas, further reducing input of large woody debris to streams. Aerial photographs from the 1940s show that riparian canopies had narrower openings over the streams and contained a larger proportion of conifers. Besides "resetting" the riparian vegetation, the 1955 and 1964 floods also redistributed large woody debris in the stream network. Following timber harvest and other disturbances, many streamside forests have regenerated mostly in hardwoods, especially alder. Along the lower Smith River, areas of the flood plain that formerly supported riparian forests are now dedicated to other uses.

Large woody debris loading in streams will be affected for many years and decades by past logging practices, stream clearing activities, and the mid-century floods. Following timber harvest, large woody debris in streams is expected to decrease for 50 to 100 years (Bryant and Sedell 1995). Where redwoods are present in the riparian zone, declines in large woody debris may be more gradual due to rot resistance of this species.

Except in unusual cases when funding and access are available for transporting and adding wood to streams, future trends in large woody debris in streams are tied to future trends in riparian vegetation. Recruitment of large woody debris into streams depends on the growth of suitable trees in the riparian zone. Conifer regeneration is particularly important because conifers provide the largest and longest-lasting woody debris. In riparian areas that are now covered primarily with young hardwoods, natural succession to conifers will take decades. When conifers are allowed to grow to large sizes in the riparian area, large woody debris in streams will gradually increase over decades and centuries. It is difficult to overstate the importance of conifer regeneration in riparian areas.

On both public and private land, fire is always a potential influence on vegetation including riparian vegetation. However, catastrophic loss is unlikely. Another destructive agent is attacking riparian trees in areas of serpentine soils, such as in the North Fork subbasin. An important riparian conifer, Port Orford cedar, is declining in abundance due to root rot disease. Although these riparian forests have an open character due to the harsh soil, the decreased abundance of Port Orford cedar will probably have a deleterious effect on large woody debris loading, water temperature, and consequently stream habitat quality.

In some cases, formation of large woody debris structures in streams is limited by the presence of road networks especially bridges. During extreme peak flows, as trees are swept down stream, logs tend to gather in low gradient areas where they catch on a solid feature. All too often the solid feature is a bridge support. Subsequently, the log jam is removed from the stream channel by highway maintenance crews. Under natural conditions, log jams formed during peak flows would persist and provide important fish habitat for many years.

On public lands, riparian protection policies of the Smith River NRA and the Northwest Forest Plan will eventually result in production of large conifers in riparian areas which will gradually renew supplies of large wood in streams. On private timber lands, trends in riparian vegetation and large woody debris depend largely on forest practice regulations. Almost all the private lands in the Smith River watershed are in California and are under the jurisdiction of California Forest Practice Regulations. These rules require timber operators to retain 50% of both the overstory and understory canopy and 25% of the conifer canopy. However the rules do not result in the retention of large conifers except for "the retention of two living conifers per acre at least 16 inches diameter breast height and 50 feet tall within 50 feet" of the stream. In contrast, the Oregon Forest Practice Rules require retention of a large amount of conifer basal area while also allowing more opportunity for opening the canopy to initiate conifer regeneration. Under the California rules, conifer regeneration in riparian areas is more difficult due to shade retention requirements (Appendix E). Because high stream temperatures are not a pressing problem in the Smith River watershed, forest practice rules should place a greater emphasis on development of future sources of large woody debris and less emphasis on retention of maximum shade.

Although in most cases the amount of shade and nutrients contributed to the stream by riparian areas is probably sufficient, many riparian areas probably contain fewer large conifers than prior to European American settlement. This results in a slow rate of production of large woody debris that probably restricts the recovery of anadromous fisheries. Decreased amounts of woody debris throughout the Smith River system, especially in the estuary, lower river, and lower tributaries, are probably an important reason for the decline in anadromous salmonid populations from historic levels.

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