Large roots dominate the contribution of trees to slope stability

Giadrossich, Filippo; Cohen, Denis; Schwarz, Massimiliano; Ganga, Antonio; Marrosu, Roberto; Pirastru, Mario; Capra, Gian Franco (2019). Large roots dominate the contribution of trees to slope stability Earth Surface Processes and Landforms, 44(8), pp. 1602-1609. Wiley 10.1002/esp.4597

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Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field‐measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd.

Item Type:

Journal Article (Original Article)


School of Agricultural, Forest and Food Sciences HAFL > Multifunctional Forest Management


Giadrossich, Filippo;
Cohen, Denis;
Schwarz, Massimiliano0000-0003-4652-8102;
Ganga, Antonio;
Marrosu, Roberto;
Pirastru, Mario and
Capra, Gian Franco


G Geography. Anthropology. Recreation > GE Environmental Sciences
S Agriculture > SD Forestry








Nadine Werndli

Date Deposited:

17 Sep 2019 10:47

Last Modified:

18 Dec 2020 13:28

Publisher DOI:





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