timber harvest

Local & Downstream Impacts of Contemporary Forest Harvesting Practices on Watershed Hydrology
Zègre, N.

This study measured the impacts of two harvest entries on the monthly streamflow and other measures of the streams below and adjacent to harvest.  Statistically significant increases in sediment yield, as suspended sediment, were detected as a consequence of timber harvest in the South Fork Hinkle Creek. These increases were detected at the small, headwater watershed scale as well as the large watershed scale. Unlike the increases in water yield, these increases were not consistent with the literature. The results of the seminal paired watershed studies showed very large increases in sediment yield, often as much as two or three times greater than sediment yields before timber harvest. The results from contemporary forest practices are much more muted and the increases are in the range of 20 to 30 percent increases in sediment yield. The increases are in order with and correlate well with the increases in water yield. That the increases in sediment yield are a result of increased stream power due to increases in water yield is a reasonable hypothesis to put forward to explain these observations. The greatest improvement in forest practices over the past several decades were directed toward reducing the impacts of timber harvest on sediment yield. These improvements include; clearcut size limits and adjacency constraints, improved yarding systems (in this case slackline, skyline cable systems), the prescription of buffer strips, and changes in site preparation practices.

DISCIPLINE: Hydrology & Water Quality    STUDY: Hinkle Creek    TYPE: Presentations    TAGS: Streamflow, peak flow, Harvesting effects, timber harvest, Headwater streams
The Influence of Contemporary Forest Management on Stream Nutrient Concentrations in an Industrialized Forest in the Oregon Cascades
Meininger, W.S., K. Cromack, and A. Skaugset

Fertilizer was applied in 2004 and the response of the nutrient levels in the water was measured. Stream water samples were analyzed for nitrogen, phosphorus, calcium, sodium, potassium, magnesium, sulfate, chloride, and silicon as well as specific conductance, pH, and alkalinity. All treatment watersheds showed a statistically significant increase in NO3 + NO2 concentrations after clearcutting (p < 0.001). The slope of the streambed through the disturbance was a stronger predictor of the magnitude of the response than was the magnitude of disturbance. Ammonia and organic nitrogen displayed notable increases after harvest treatment, but these increases were attributed to increases in the control watersheds. Phosphorus showed a response to timber harvest in one headwater stream. The remaining nutrients showed a small decrease in the control and treatment watersheds for the period after harvest. The storm response results showed that NO3 + NO2 concentrations in stream water increase with discharge during small storms that occur after periods of negligible precipitation.

DISCIPLINE: Hydrology & Water Quality    STUDY: Hinkle Creek    TYPE: Presentations    TAGS: timber harvest, Nitrate Response, topography, clearcut
Short-term Relationship of Timber Management and Pacific Giant Salamander Populations, and the Response of Larval Stream Amphibian to Predators Under Different Sediment Levels
Leuthold, N.

In the Pacific Northwest, multiple studies have found negative effects of timber harvest on stream amphibians, but the results have been highly variable and region-specific. Over the last 30 years forest management practices have changed substantially, yet little work examines how modern forest management relates to the abundance or density of stream amphibians. I examined the influences of contemporary forest practices on Pacific giant salamanders as part of the Hinkle Creek paired watershed study. Density was positively associated with substrate, negatively associate with upstream area drained, and had a weak positive association with fish density, but I found no evidence of an effect of harvest. Pacific Northwest stream amphibians are often negatively associated with sedimentation, but the mechanism underlying this relationship is not clear. I found amphibian larvae were more visible as sediment level increased and some evidence that larvae were less visible in the presence of fish. These patterns are consistent with the hypothesis that sediment affects larval stream amphibians by increasing vulnerability to predation.

DISCIPLINE: Amphibians    STUDY: Alsea, Hinkle Creek, Trask    TYPE: Theses    TAGS: timber harvest, stream amphibians, Pacific giant salamanders, mark-recapture analysis, predation, Larva
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