Hillslope soils and vegetation

Amundson, Ronald; Heimsath, Arjun M.; Owen, J. J.; Yoo, Kyungsoo; Dietrich, W. E.

doi:10.1016/j.geomorph.2014.12.031

Cited by 96 publications

(85 citation statements)

References 63 publications

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“…For vegetated basins, the spatiotemporal distribution of root reinforcement has a major impact on the dynamic of sediment transport at the catchment scale (Sidle and Ochiai, 2006) and on the availability of productive soil, a key resource for human needs. At the hillslope scale, the presence of vegetation generally increases soil thickness, lowering the frequency of landsliding events but increasing their magnitudes (Amundson et al, 2015). At the catchment scale, vegetation causes slopes to steepen and sediment mobilization is then often dominated by deep landslides driven by fluvial incision (Larsen and Montgomery, 2012).…”

Section: Background and Motivationmentioning

confidence: 99%

Tree-root control of shallow landslides

Cohen

Schwarz

2017

Earth Surf. Dynam.

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Abstract. Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models usually include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the selforganized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. The variation in root stiffness with diameter can, in some cases, invert this relationship. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of this force is comparable to the slope-perpendicular tensile force. In this case, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, a crack parallel to the slope forms near the top of the hillslope. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, intermediate-sized roots (5 to 20 mm in diameter) appear to contribute most to root reinforcement. Our results show more complex behaviors than can be obtained with the traditional slope-uniform, apparent-cohesion approach. A full understanding of the mechanisms of shallow landslide triggering requires a complete re-evaluation of this traditional approach that cannot predict where and how forces are mobilized and distributed in roots and soils, and how these control shallow landslides shape, size, loc...

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Section: Background and Motivationmentioning

confidence: 99%

Tree-root control of shallow landslides

Cohen

Schwarz

2017

Earth Surf. Dynam.

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“…Microrelief of forested hillslopes is shaped by ongoing interactions between abiotic processes of weathering and soil formation, downslope regolith displacement, surface runoff, and biotic factors, among which, tree growth and decay are of major importance (Roering et al 2010;Šamonil et al 2014;Amundson et al 2015;Schaetzl and Thompson 2015). The generally slow rate of these processes may be upset and hastened by catastrophic events which disturb or even completely reorganise the geo-ecosystem.…”

Section: Introductionmentioning

confidence: 99%

Deciphering the history of forest disturbance and its effects on landforms and soils – lessons from a pit-and-mound locality at Rogowa Kopa, Sudetes, SW Poland

Pawlik

Musielok

Migoń³

et al. 2017

Bulletin of Geography. Physical Geography Series

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Abstract. The historical dimension of pit-and-mound topography has been studied at the Mt Rogowa Kopa locality, Stołowe Mountains, SW Poland. This site represents one of the best developed regional examples of hummocky forest floor relief due to widespread tree uprooting and subsequent degradation of root plates. Through map analysis and dendrochronology the disturbance history was traced to at least the 1930s and, most likely, a strong wind episode from 1933 was the reason for the forest calamity that resulted in the nearly total destruction of the original stand. However, the affected forest was a planted Norway spruce monoculture, introduced and managed until at least the beginning of the 20 th century, and not a natural forest. The windthrow niche was then used by beech, whose individuals preferentially chose mounds to grow, conserving the hummocky microtopography. Changes in soil evolutionary pathways brought about by wind-driven disturbance include both haploidisation (rejuvenation) and horizonation (differentiation). Evidence of soil rejuvenation includes a decrease in organic carbon content and an increase in pH in the upper parts of soils developed on mounds relative to the pH of undisturbed references soils. Soil texture was relatively homogenised in pits and mounds. Dating of the pit-and-mound microrelief by means of soil properties (organic carbon content, iron forms) was only partly successful. Although the young age of pits and mounds is evident, the actual age inferred from soil properties was underestimated by a few tens of years. Evaluation of factors potentially controlling the propensity to widespread treethrow suggests that the type of forest is a far more important variable than local abiotic factors of bedrock geology, regolith characteristics, and slope inclination.

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“…Soil production is related to climatic variation (Amundson et al, 2015), with this variation partly captured by EEMT and TPE, leading to the slightly stronger predictive power of the model. However, soil production is also highly influenced by redistributive hillslope process, chemical and physical weathering, and tectonic uplift (Heimsath et al, 1997;Riebe et al, 2004;Yoo and Mudd, 2008b) and can be a highly nonlinear process (Pelletier and Rasmussen, 2009a).…”

Section: Model Results For Chronosequencesmentioning

confidence: 99%

A probabilistic approach to quantifying soil physical properties via time-integrated energy and mass input

Shepard

Schaap

Pelletier

et al. 2017

SOIL

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Abstract. Soils form as the result of a complex suite of biogeochemical and physical processes; however, effective modeling of soil property change and variability is still limited and does not yield widely applicable results. We suggest that predicting a distribution of probable values based upon the soil-forming state factors is more effective and applicable than predicting discrete values. Here we present a probabilistic approach for quantifying soil property variability through integrating energy and mass inputs over time. We analyzed changes in the distributions of soil texture and solum thickness as a function of increasing time and pedogenic energy (effective energy and mass transfer, EEMT) using soil chronosequence data compiled from the literature. Bivariate normal probability distributions of soil properties were parameterized using the chronosequence data; from the bivariate distributions, conditional univariate distributions based on the age and flux of matter and energy into the soil were calculated and probable ranges of each soil property determined. We tested the ability of this approach to predict the soil properties of the original soil chronosequence database and soil properties in complex terrain at several Critical Zone Observatories in the US. The presented probabilistic framework has the potential to greatly inform our understanding of soil evolution over geologic timescales. Considering soils probabilistically captures soil variability across multiple scales and explicitly quantifies uncertainty in soil property change with time.

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Hillslope soils and vegetation

Cited by 96 publications

References 63 publications

Tree-root control of shallow landslides

Tree-root control of shallow landslides

Deciphering the history of forest disturbance and its effects on landforms and soils – lessons from a pit-and-mound locality at Rogowa Kopa, Sudetes, SW Poland

A probabilistic approach to quantifying soil physical properties via time-integrated energy and mass input

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