The role of trees in the geomorphic system of forested hillslopes — A review

Pawlik, Łukasz

doi:10.1016/j.earscirev.2013.08.007

Cited by 101 publications

(68 citation statements)

References 115 publications

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“…The biomechanical effect of trees on soils has repeatedly been described on the fine scale of disturbed microsites (reviews by Šamonil et al, 2010a;Pawlik, 2013). Studies have revealed changes in the rate as well as the trajectory of pedogenesis (e.g.…”

Section: Discussionmentioning

confidence: 99%

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

et al. 2014

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Abstract. Biota–soil interactions in natural ecosystems are the subject of considerable research. Our hypothesis is that individual trees play a significant role through biomechanical and biochemical disturbances affecting soil formation in temperate forests, resulting in a complex spatial pattern of disturbance regimes and a close relationship between disturbance histories and soil units. In Žofínský Prales (Czech Republic) – the fourth oldest, continuously protected reserve in Europe and the first site of global research network SIGEO (Smithsonian Institution Global Earth Observatories) in continental Europe – we compared extensive dendrochronological, soil and pit–mound microtopography data both temporally and spatially from an area of anthropogenically unaffected 42 ha collected from 2008–2012. These data sets differ in terms of information complexity and length of memory: tree cores contain complex information about the disturbance history of the past 350 years, footprints of disturbances from the uprooting of a specific tree can persist 1700 years, and soils represent an extensive composite phenotype that has been developing for at least the entire postglacial period (10 500 years). On average, 6.18–13.41% of the canopy on individual soil units was disturbed per decade. Even though the "backbone" of key events in the development of the forest ecosystem remained the same (e.g. the 1870s, 1880s and 1980s), the internal structure of disturbance history often differed among soil units; the most exceptional were Gleysols and Histosols, where important feedback from soil to trees was expected. However, the characteristics of treethrow dynamics as well as the frequencies of stronger releases in core series also significantly differed along a gradient of terrestrial soil weathering and leaching (Haplic Cambisols – Dystric Cambisols – Entic Podzols – Albic Podzols). These results suggest the existence of several disturbance regimes within the forest, controlling fine-scale pedodiversity.

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Section: Discussionmentioning

confidence: 99%

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

et al. 2014

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“…In the long term, the presence of vegetation (i) increases soil production rates through mechanical and chemical processes (Wilkinson et al, 2005;Phillips et al, 2008) (100-1000 years); (ii) increases soil residence time on hillslopes due to root reinforcement and protects against runoff erosion (Istanbulluoglu and Bras, 2005) (10-100 years; note that in the case of natural or human driven disturbances, the response time of the system (i.e., root decay) is of the order of a few years (Vergani et al, 2016)); and (iii) enhances soil diffusion rates on hillslopes due to tree wind throw (Pawlik, 2013;Roering et al, 2010), root mounds (Hoffman and Anderson, 2014), and biological activity (Gabet and Mudd, 2010) (100-1000 years).…”

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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“…Forest structure (e.g., tree density or canopy cover) is intricately linked to biogeochemical cycling and the regional climate (Bonan 2008), and is a key stabilizing process for the geomorphology of hillslope ecosystems (Pawlik 2013). In general, models that predict future biogeographic distributions are lacking good data on population dynamics over time (Kearney and Porter 2009).…”

Section: Introductionmentioning

confidence: 99%

Changing forest structure across the landscape of the Sierra Nevada, CA, USA, since the 1930s

et al. 2014

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Understanding the dynamics of forest structure aids inference regarding future forests and their distributions around the world. Over the last few decades, several papers have addressed changing forest structure in the Sierra Nevada, CA, USA, but these studies were limited in scope. We carried out a broad comparison of forest density and composition in the 1930s versus the 2000s for the west slope of the central and northern Sierra Nevada, using the two most extensive data sets available. Forests in this region have endured a long, complex history of human disturbance, and are now experiencing climatic shifts. We subdivided the landscape into elevation and latitude zones and compared historical and modern tree densities within each zone. We compared densities in historical plots to burned and unburned modern plots, as well as densities of individual tree species in historical vs. modern plots for their entire elevational distribution. Density of small trees (10.2–30.4 cm dbh) was significantly higher in the modern data set for all elevations and all latitudes, ranging from 20 to 148% higher. However, density of large trees (≥61.0 cm) was lower in the modern data set for most elevations and latitudes, ranging from 41% to 60% lower in most zones. Density difference of mid‐sized trees (30.5–60.9 cm) was mixed, but was generally higher in modern plots. The pattern of more small trees but fewer large trees held for most individual species as well, but with notable exceptions. Our comparison of burned and unburned plots strongly implicates fire suppression as a driver of increased density of small trees in low‐ to mid‐elevation forests. However, modern high‐elevation (>2500 m) forests, where fire suppression impacts should be minimal, were also significantly denser than historical plots. Changing climatic conditions may be driving increased densities of small trees in high elevations, as well as decreased densities of large trees across the region.

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The role of trees in the geomorphic system of forested hillslopes — A review

Cited by 101 publications

References 115 publications

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

Tree-root control of shallow landslides

Changing forest structure across the landscape of the Sierra Nevada, CA, USA, since the 1930s

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