Root reinforcement dynamics in subalpine spruce forests following timber harvest: a case study in Canton Schwyz, Switzerland

- We estimated root reinforcement 5, 10, 15 years after timber harvest in spruce stands.
- We collected new experimental data about root distribution and mechanical properties.
- We developed a new model for the estimation of root reinforcement decay during time.
- 5 year from harvest the root reinforcement is the 40% of a live forest.
- 15 years from harvest a spruce forest provides no reinforcement.

Root reinforcement is a key factor when dealing with slope stability problems and is an important quantitative criterion for the evaluation of the protective function of forests against shallow landslides, as well as for the adoption of appropriate practices in protection forest management. Although many models have been developed to estimate root reinforcement, a reliable quantification that considers both its spatial and temporal variability still remains a challenge. This work aims to extend the understanding of the long term spatial and temporal dynamics of root reinforcement after forest harvest in subalpine spruce forests by supplying new experimental data and applying a state-of-the-art model.We estimated root reinforcement decay 5, 10 and 15 years after timber had been harvested in spruce stands in a small catchment in the Swiss Alps. We collected root distribution data at different distances from the trees and calibrated and validated a root distribution model (RootDis). To estimate root mechanical properties, we tested roots up to 12 mm diameter in the field, and computed root reinforcement for each case study with the Root Bundle Model. Finally, we developed a new model for the estimation of root reinforcement decay, based on the observed change in root distribution after felling and on the decay of the root pullout force. The final result is a model for the spatial-temporal prediction of root reinforcement heterogeneity and dynamics in subalpine spruce forest stands. Five year old harvested spruce forest in the climatic conditions of the study area provides 40% of the root reinforcement of live forest, while 15 years old harvested forest provides no reinforcement at all. Shrub species and natural regeneration could guarantee almost the 30% of the root reinforcement of a live forest after 15 years from cutting. Additional work is now required to further validate the model and implement these results in a slope stability analysis.