Effects of forest cover, topography, and sampling extent on the measured density of shallow, translational landslides

[1] We use regionally available digital elevation models and land cover data, calibrated with groundand photo-based landslide inventories, to produce spatially distributed estimates of shallow, translational landslide density (number/unit area). To discern effects of land use, we focus on resolving landslide density relationships with forest cover. We account for topographic variability between sites and landslide detection bias in air photo mapping. Even so, for sites in the Oregon Coast Range, we find great variability in the ratios of landslide density in forest classes among sites. We present strategies for subsampling available data to quantify this variability. For these data, we find that older forests, when sampled over tens of square kilometers, commonly exhibited the highest landslide densities but over hundreds of square kilometers always exhibited the lowest densities, averaging 30% of that in recently harvested areas and 79% of that in younger, managed forests.