Forest Investment Account

Abstract of FII Project R02-37

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Variable retention and the conservation of small streams and their riparian areas

Author(s): Beese, Bill
Imprint: Victoria, B.C. : British Columbia Forest Investment Account, 2003
Subject: Variable retention harvesting, Riparian Ecology, British Columbia, Stream ecology, Vancouver Island
Series: Forest Investment Account (FIA) - Forest Science Program


Small headwater streams receive little protection under forest practices guidelines, yet such streams may be important for maintaining the productive capacity of downstream fish habitat by processing and exporting nutrients, organic matter and stream invertebrates. The current study was initiated to evaluate the response of small streams to the new Variable Retention (VR) approach to forest management being applied throughout coastal BC forests. Three sites, one at Lewis Lake near Powell River, one in the White River drainage near Sayward and the other near Kennedy Lake were chosen for the main study. Several other streams in the Tsitika River drainage are being studied as part of a PhD thesis. Of the three sites, Kennedy Lake is unique in its geomorphological features, chemical composition and biological community structure. Pre-logging surveys of streams at all the sites identified disparities between adjacent, similar-looking streams both in nutrient chemistry and benthic communities, emphasizing the need for extensive pre-treatment data sets. High variability in nitrate levels both within and between streams at the Lewis Lake and White River sites preclude any generalization about potential for P or N limitation. In contrast Kennedy Lake streams appear to be more consistently N-limited. Extremely low flows during the late summer/early autumn led to very low concentrations of dissolved organic carbon (DOC; 1 mg/L2 mg/L) at the Lewis Lake and White River sites and UV impacts may be observed following thinning of streamside canopies at those sites. On the other hand, DOC levels at Kennedy Lake were sufficiently high (10 mg/L20 mg/L) to block UV. Low rainfall also led to intermittent flow in many streams with disconnected pools. Algal and bacterial biomass was low in all streams but algal communities were consistently higher and bacterial numbers lower in Lewis Lake streams compared to streams at White River.
Bill Beese...[et al.]

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Updated August 02, 2006 

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