Effects of root tensile force and diameter distribution variability on root reinforcement in the Swiss and Italian Alps

Root reinforcement is considered to be one of the most important factors contributing to the stability of vegetated hillslopes; however, its estimation is still challenging because of the spatial variability of root distribution and root mechanical properties. This work uses the root bundle model to assess the sensitivity of root-reinforcement estimation to the variability in both root mechanical properties and root distribution. We used a large data set of root tensile tests and root distributions of an important alpine species, Picea abies (L.) Karst., collected in a wide range of altitudinal and climatic ranges on both north and south sides of the alpine mountain range. The results demonstrate that the site-specific characterization of mechanical properties and root distribution is fundamental for the quantification of root reinforcement at the stand scale. Root diameter distribution plays a dominant role in influencing the root-reinforcement model’s output; however, in contrast with results from other works, differences in root diameter–force functions are significant and cannot be ignored. Model results also show that coarse roots contribute significantly more to the reinforcement of soil than fine roots, underlying the need of additional data for roots with diameters larger than 5 mm.