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Erosion rates derived using dendrogeomorphology have been used to quantify slope degradation in many localities globally. However, with the exception of the western United States, most of these estimates are derived from short-lived trees whose lifetimes may not adequately reflect the complete range of slope processes which can include erosion, deposition, impacts of extreme events and even long-term hiatuses. Erosion rate estimates at a given site using standard techniques therefore reflect censored local point erosion estimates rather than long-term rates. We applied a modified dendrogeomorphic approach to rapidly estimate erosion rates from dbh/age relationships to assess the difference between short and long-term rates and found that the mean short-term rate was ~ 0.13 cm/yr with high variability, while the uncensored long-term rate was ~ 0.06 cm/yr. The results indicate that rates calculated from short-lived trees, while possibly appropriate for local short-term point estimates of erosion, are highly variable and may overestimate regional long-term rates by > 50%. While these findings do not invalidate the use of dendrogeomorphology to estimate erosion rates they do suggest that care must be taken to select older trees that incorporate a range of slope histories in order to best approximate regional long-term rates. [ABSTRACT FROM AUTHOR]

The advent of high-resolution, precise, back-pack portable terrestrial lidar scanners (TLS) provides a revolutionary new tool for obtaining quantitative, high-resolution (2-mm to 30-mm point spacing) measurements of landscape surface features. Moreover, data collected using these instruments allow observation of geomorphic processes in systems that can experience change on a daily basis. We have introduced TLS techniques in ongoing investigations of semiarid landscapes associated with weakly cemented sandstones along part of the Black Mesa escarpment of NE Arizona. Clay-cemented, Jurassic sandstones exposed along this escarpment are sensitive to moisture, and thus climate, via hydration-expansion weathering of interstitial clay. Sediment shed from weathered slopes has caused locally rapid valley floor aggradation and upper basin slope vertical denudation rates of 2–3 mm/yr over 10- to 100-yr timescales, as indicated by dendrochronology coupled with soil geomorphic analysis. These rates suggest rapid hillslope denudation rates. Employing the University of New Mexico Lidar Laboratory Optech Ilris 3D TLS, we are constructing a high-resolution model of two major basins along the escarpment. Focusing on a single, small (30 × 60 m) area of a mostly non-vegetated, steep slope (>35°), we demonstrate in this paper a method of comparative analysis of pointcloud data sets that can detect subcentimeter change resulting from a single season of monsoon precipitation along the escarpment. Using repeat scans can provide an empirical evaluation of single season erosion rates in the study site, and because our observations are geospatial in nature, we can also document the parts of the slopes that make the greatest contribution to local valley floor aggradation. In demonstrating the utility of this method, we expect that continued investigation of this site will provide insight to the key processes associated with soil-mantled versus bedrock-dominated slopes during modern escarpment retreat and hillslope modification, which, in turn, may further elucidate the impacts of Holocene climate change on this rapidly evolving landscape. [ABSTRACT FROM AUTHOR]