Root reinforcement dynamics of European coppice woodlands and their effect on shallow landslides: A review

Abstract

In European mountain regions, forests play an important role in the mitigation of risk due to natural hazards such as landslides, rockfalls, floods and avalanches.\ud \ud Conifer species usually provide a protective effect at higher altitude, while at lower altitudes broadleaf species are dominant. These forests are or were often managed as coppice systems.\ud \ud The high stem density of coppice stands, their rapid growth and the permanence of root systems in the soil can be considered as assets in terms of protective function. However, these considerations are poorly researched and there is generally a lack of studies investigating the suitability of coppice as protection forests. The issue is relevant, considering that many coppice stands in mountain regions have become uneconomic and are now abandoned and overaged. Whether and how to manage these forests stands is a key question for practitioners.\ud \ud In this contribution we analyze the implications of coppice management for slope stability and in particular to mitigate shallow landslides, focusing on root reinforcement, the main mechanism by which vegetation can reinforce slopes.\ud \ud We review available studies concerning root distribution and dynamics in coppice stands to formulate hypotheses about their contribution in terms of root reinforcement. Finally we highlight the lacks of knowledge and the further steps needed to properly evaluate the effectiveness of the coppices in protecting against shallow landslides

Mechanical Characteristics of the Fine Roots of Two Broadleaved Tree Species from the Temperate Caspian Hyrcanian Ecoregion

“…Root reinforcement has been noticed as one of the key factors when dealing with slope stability issues and landslides safety, thereby becoming one of the criteria in managing forests against natural hazards [10,11]. Large roots anchor the soil, especially across planes of weakness, and fine roots provide an extensive network that increases soil shear strength [6,48,49]. While coarse roots (>10 mm) have a higher impact on root reinforcement than fine roots [6,7], fine roots are more numerous and occupy a larger area around the tree on slopes than do coarse roots [50], playing a key role in slope stability.…”

“…Large roots anchor the soil, especially across planes of weakness, and fine roots provide an extensive network that increases soil shear strength [6,48,49]. While coarse roots (>10 mm) have a higher impact on root reinforcement than fine roots [6,7], fine roots are more numerous and occupy a larger area around the tree on slopes than do coarse roots [50], playing a key role in slope stability. Most of the scientists consider that fine and thin roots (<10 mm), which act as tensile fibers during slope failures, provide the major contribution to slope stability [15][16][17]51].…”

“…Vegetation, especially in the mountain regions, plays a remarkable role in stabilizing slopes and protecting soil from erosion and landslides [2,3]. Particularly for trees, roots are known to reinforce soil through three mechanisms [4][5][6][7]: basal root reinforcement, lateral root reinforcement, and increasing the stiffness of the root-soil composite material. In all of these mechanisms, the contribution of roots is defined by their mechanical properties (strength and elasticity) [4,5,[8][9][10] and their density and spatial distribution [4,6,9,11], although species, environment, root diameter, root branching order, age of the trees, root architecture, and forest structure are known to influence root reinforcement variability [12][13][14].…”

Large roots dominate the contribution of trees to slope stability

“…Roots reinforce soil in three ways: basal root reinforcement, stiffening and buttressing of sliding mass under compression, and lateral root reinforcement (Vergani et al. ). Basal root reinforcement occurs when roots cross the shear plane and is highly efficient in stabilizing vegetated slopes.…”

A critical analysis of Vacca, A., Aru, F., and Ollesch, G. (2017). Short‐term impact of coppice management on soil in a Quercus ilex L. Stand in Sardinia. Land Degradation & Development, 28(2), 553–565

“…Soil disturbances are possible after coppice harvesting (Marchi et al, ) as a function of specific site characteristics (slope gradient, presence of dead wood, and litter), harvesting processes (use of mechanical means and release and distribution of the branches), and precipitation trends (seasonality and rainfall intensity). However, good silvicultural practices and fast regrowth of vegetation limit the risk of erosion (Piussi & Zanzi Sulli, ; Grohmann, Savini, & Frattegiani, , Vergani et al, ). In coppice forests, within 3–5 years, tree canopies usually cover the ground and the beating action of precipitation on the soil, as well as the browsing of ungulates, ceases (Casula & Murgia, ).…”