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Historic logging practices as a landforming factor in South-west Germany


Summary:


In low mountain range forested areas in Germany historic erosion gullies are a common phenomenon in the local topography. It is supposed that they result from historic logging practices, i.e. by dragging logs downhill with oxen or horses. In the course of mechanization in forestry in the second half of the 20th century, logging was concentrated on terrain-adapted access lines with substantially reduced erosion risk. However, the introduction of new crawler harvesters working in the direct line downhill on steep slopes may again produce a high erosion risk.

The aim of this study is to understand historic processes and to assess the erosion risks caused by present logging practices. We hypothesize that dragging of logs directly affects soil erosion by 3 ways: Soil material is directly moved downward, the soil surface is scarified and/or compacted, and flow paths with reduced roughness are formed. As soon as erosion has formed a furrow, an autocatalytic increase of erosion may occur by runoff concentration and sediment delivery from steep edges.

For three forest sites high-resolution digital elevation models (DEM) have been calculated based on airborne laser scanning data with a point density of approximately 0.5 points per m2. By algorithmic analyzing of cross profiles through the gullies, the eroded cross sections have been calculated and the original terrain surfaces reconstructed. Soil losses by rain are being estimated with the help of forest WEPP interfaces. Soil transport and mobilization by dragged logs are being experimentally assessed by a new developed tracer technique.

By successive erosion of the DEM we also try to reconstruct the erosion history by modelling possible flow concentrations in the newly formed channels.



Duration: 01.04.2004 - 31.03.2007

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