Root strength and density decay after felling in a Silver Fir-Norway spruce stand in the Italian Alps

Aims: Forests induce a mechanical reinforcement of soil, generally quantified in terms of additional root cohesion (cr), which decreases due to root decay after felling. The aim of this work is providing new field data on soil reinforcement by roots after trees cutting. Methods: The present work investigated cr decay in a mixed Silver Fir-Norway Spruce (Abies alba Mill. Picea abies (L.) Karst.) stand in the Italian Alps over a period of 3 years after felling by monitoring the two cr driving variables: root tensile resistance and root density. Results: Results showed that a significant difference in root resistance occurred only 3 years after felling, whereas the decrease in the number of roots was significant in the second year. The degradation process was more rapid in shallower layers and for thinner roots, as a consequence of the pattern of biological activity rate. The reduction of cr after felling was, for a reference profile depth of 70 cm, 55 % in the first 2 years and another 16 % in the third year. Conclusions: The findings of this study, providing new data on the decrease of cr after felling, can be introduced into geotechnical models allowing a better estimation of the stability of forest hillslopes.