Simulating the Effects of Forest Management on Stream Shade in Central Idaho
Uneven-aged stands with multistory, diverse canopies are common throughout the forests of the Inland Northwest, and both current regulations and prescriptions under consideration often promote further diversification. Understanding the potential effects of alternative riparian management prescriptions on stream shade is important, and effects may vary with even-aged versus uneven-aged conditions. For a range of riparian stand conditions in Central Idaho, in this article, we compare shade predictions from two approaches using a widely used model introduced by Chen et al. in 1998, one that accounts for multiple canopies (“canopy-explicit approach”) and another that accounts for a single-layer canopy (“canopy-average approach”). We found slight improvements using the canopy-explicit approach when there were distinct overstory and understory canopies. However, we found that both approaches underpredicted shade levels observed in the field. The underestimate is influenced by the Forest Vegetation Simulator (FVS) canopy cover metric that we used to inform the model; this metric underestimates vertical nonoverlapping cover, an important input to the shade model. We used the canopy-explicit approach to evaluate effects of the Idaho Forestry Program (IFP), a major conservation agreement that the State of Idaho is currently pursing with federal agencies, on stream shade. For this evaluation, we compared shade predicted to occur through implementation of the IFP with that from passive (no harvest) management. For the IFP, we found that shade reduction would be approximately 5%, on average, largely because of the effect of the 25-ft stream-adjacent no-harvest zone that this alternative requires. We also compared shade produced under the IFP with shade targets developed by the Idaho Department of Environmental Quality. Predicted IFP shade levels were lower than target levels, in large part because of the effect of the FVS cover metric. Overall, these comparisons highlight the usefulness of the approach in comparing the effects of different management alternatives on shade, despite the bias introduced by using the FVS cover metric and problems inherent in comparing results developed through simulation to targets based on different methods.
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Document Type: Research Article
Publication date: 2013-01-01
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- Each regional journal of applied forestry focuses on research, practice, and techniques targeted to foresters and allied professionals in specific regions of the United States and Canada. The Western Journal of Applied Forestry covers the western United States, including Alaska, and western Canada; WJAF will also consider manuscripts reporting research in northern Mexico that has potential application in the southwestern United States.
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