WHFF Project: 2016.10
Project leaders: Jean-Jacques Thormann and Massimiliano Schwarz
The most important facts in brief
The succession of root reinforcement of a stand after forest fire, and thus the dynamics of the protective effect against shallow landslides were characterized and quantified for the first time
Current vegetation development in the forest fire areas of Visp and Leuk in Valais, Müstair in Grisons and Cugnasco in Ticino were surveyed and compared with old WSL data sets.
The root system of the tree species spruce, beech, sweet chestnut, downy oak, Scots pine, birch, as well as the neophytes Götterbaum and Chinese hemp palm were recorded in the field
There is a large difference in the root reinforcement dynamics of each tree species after a forest fire. The wildfire intensity also has a significant influence on the regeneration rate of the system.
In general, the highest stabilizing effect of the studied tree species is expected for beech and sweet chestnut. The remaining tree species (Scots pine, birch, goddess tree, hemp palm) develop only a low effect
Project description
Forests are dynamic ecosystems that are subject to various disturbances such as fire, storms, diseases, and insects. These disturbances are part of the natural dynamics of forests, but can be problematic in protection forests because they can temporarily or permanently reduce the protective effect.
Protection forest management aims at influencing forest dynamics to ensure optimal and continuous protective effects. The regeneration time depends on several factors, such as the state of the forest ecosystem before the disturbance, the intensity and type of disturbance, the nature of the natural hazard, and environmental conditions.
The objective of this project is to assess the post-fire resilience of forest ecosystems and quantify the dynamics of their protective effect against shallow landslides. In particular, it should be possible to estimate the time required by forest ecosystems to reach a sufficient level of root reinforcement, taking into account the different possible regeneration scenarios.
For this purpose, the current vegetation development in the forest fire areas Visp and Leuk in Valais, Müstair in Grisons and Cugnasco in Ticino was surveyed and compared with old data sets of WSL. Thus, the increment as well as the change in tree species composition and stand density can be seen. In addition, to determine the vegetation dynamics of individual tree species, LFI datasets were analyzed to estimate the BHD increment of each tree species at different elevation levels. Next, the root systems of the tree species spruce, beech, sweet chestnut, downy oak, Scots pine, birch, as well as the neophyte goddess tree and Chinese hemp palm were recorded in the field.
On the one hand, individual roots were examined for their maximum absorbable tensile force, and on the other hand, the root quantity and root distribution were determined. With these parameters, the root bundle model according to Schwarz et al. (2010b, 2013) can be used to calculate the lateral and basal root reinforcement dynamics for each tree species, depending on stand density and average BHD.
Conclusions
The results show a large difference in the root reinforcement dynamics of each tree species after a forest fire. The forest fire intensity also has a significant influence on the regeneration speed of the system. In general, the highest stabilizing effect of the studied tree species is expected for beech and sweet chestnut. A medium contribution to slope stability is present in spruce and downy oak. The remaining tree species (Scots pine, birch, goddess tree, hemp palm) have only a minor effect.
With the acquired knowledge, a decision tree for practice was created, which provides an aid for deciding the necessary measures depending on the forest fire case in the protection forest against shallow landslides.
Here you can download the full final report:
You can find more information about the project on ARAMIS.
The project was supported by the Swiss Forest and Wood Research Funding Switzerland (FOWO-CH) of the Federal Office for the Environment (FOEN) and the Conference for Forests, Wildlife and Landscape of the cantons.