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The Rapid Technique: A New Method for Evaluating Downstream Effects of Forest Practices on Riparian Zones
Excerpt from The Rapid Technique
This technique was developed for analyzing geomorphic processes in the densely forested west side of the Cascade Range, Oregon. Differences in geology, vegeta tion, landforms, and hydrology in other regions are likely to result in different patterns of disturbance on aerial photos. This technique has not been tested in areas other than the west side of the Cascades, and its application to other regions should be considered experimental. The rapid technique was developed to help sort out the relative importance of different processes producing downstream effects. It is therefore useful to consider how downstream effects might be distinguished from each other. Downstream effects are one element in what I call the management-modified disturbance system (fig. This system is a cascading series of causes and effects, with each link in the chain both an effect of preceding causes and a cause of subsequent effects. In this model, different classes of effects are distinguished by whether they occur at the site or away from the site of primary modification. Figure 1 Â General model of the management-induced disturbance system. The disturbance system begins with a modification to the primary site for timber harvest activities; modifications might include constructing logging roads and land ings, falling and yarding timber, and preparing planting sites. These activities produce changes in local site conditions, such as compacted soils, altered ground cover, reduced root strength, opened canopies, and changes in the size distribution and volume of dead and downed woody debris. Such changes in site conditions can, in conjunction with exogenous driving events such as storms, cause changes in onsite processes, resulting in onsite effects. In the Pacific Northwest, these effects include reduced infiltration and subsurface flow, altered patterns of snow accumulation and melt, expanded drainage networks, and accelerated erosion from both surface and mass movement processes. In the disturbance system an external storm event may be required for such changes to become apparent.
This technique was developed for analyzing geomorphic processes in the densely forested west side of the Cascade Range, Oregon. Differences in geology, vegeta tion, landforms, and hydrology in other regions are likely to result in different patterns of disturbance on aerial photos. This technique has not been tested in areas other than the west side of the Cascades, and its application to other regions should be considered experimental. The rapid technique was developed to help sort out the relative importance of different processes producing downstream effects. It is therefore useful to consider how downstream effects might be distinguished from each other. Downstream effects are one element in what I call the management-modified disturbance system (fig. This system is a cascading series of causes and effects, with each link in the chain both an effect of preceding causes and a cause of subsequent effects. In this model, different classes of effects are distinguished by whether they occur at the site or away from the site of primary modification. Figure 1 Â General model of the management-induced disturbance system. The disturbance system begins with a modification to the primary site for timber harvest activities; modifications might include constructing logging roads and land ings, falling and yarding timber, and preparing planting sites. These activities produce changes in local site conditions, such as compacted soils, altered ground cover, reduced root strength, opened canopies, and changes in the size distribution and volume of dead and downed woody debris. Such changes in site conditions can, in conjunction with exogenous driving events such as storms, cause changes in onsite processes, resulting in onsite effects. In the Pacific Northwest, these effects include reduced infiltration and subsurface flow, altered patterns of snow accumulation and melt, expanded drainage networks, and accelerated erosion from both surface and mass movement processes. In the disturbance system an external storm event may be required for such changes to become apparent.
47 pages, Paperback
Published August 24, 2018
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