Changes in riparian composition and density following timber harvest and floods along Redwood Creek, California

Urner, Stacy; Madej, Mary

This is a study conducted by Humboldt State University and the USGS-BRD Redwood Field Station during 1998. Excerpts: "In the Redwood Creek basin in north coastal California, timber harvest and associated streamside landsliding altered the composition of the riparian community through harvest of streamside conifers and road construction in the riparian zone. Consequently, the interactions of riparian vegetation with channel morphology have changed, as instream woody debris became less common, channels widened, and pools became shallower and less frequent. Coho salmon have recently been listed as threatened in north coastal California, and there is widespread concern about decreases in available coho habitat in gravel-bedded coastal streams. In addition, invasion of the riparian zone by exotic plants such as Himalaya berry and Scotch broom may hinder the reestablishment of conifers in disturbed riparian zones. This project addressed three questions regarding the status of riparian zones along Redwood Creek: 1) How have the overstory riparian conditions changed in Redwood Creek and major tributaries since the advent of timber harvest and following large floods (post-1948)?, 2) What are the current distributions of conifers (Douglas fir and redwood) and exotics in the understory riparian stands in the Redwood Creek basin?, 3) What are the implications of the changes in riparian composition for the long-term potential for shading and large woody debris recruitment to this coho-bearing river? Changes in overstory riparian composition were documented through an analysis of sequential aerial photographs covering the Redwood Creek watershed (1948, 1958, 1966, 1978, 1992, and 1997). For each photo year, both the right and left channel banks were mapped. Three characteristics of the riparian condition (timber harvest history, dominant riparian vegetation, and riparian stand density) were recorded for each segment on a mylar overlay map. The presence of young (understory) conifers and exotic plants in the riparian zone will be field inventoried in the summer of 1998. Since 1948, there has been a dramatic decrease in length of uncut conifer riparian zones along Redwood Creek. In recent years some cover is returning to the channel's edge, but it is dominated by hardwoods, mostly alder, instead of redwood and Douglas fir. The lack of old-growth Dougals fir and redwood along much of the length of Redwood Creek has resulted in less shade along the channel, and on-going stream temperature studies in Redwood Creek show a concomitant increase in water temperature after disturbance, with a slight cooling trend as riparian vegetation becomes reestablished."

Changes in riparian composition and density following timber harvest and floods along Redwood Creek, California

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