Rockfall profiles in Swiss protection forests: Identification of sustainable basal area distributions across tree size classes
The protective effect of mountain forests plays a crucial role in the risk management on natural hazards, including protection against rockfall. Depending on rock size and forest structure, those forests are able to reduce the risk of rockfall considerably by slowing down or stopping rocks. In order to ensure sustainable protection against rockfall, the maintenance of the protective function of the forest is of key importance. In Switzerland, the management policy "Sustainability in protection forests" (external pageNaiS) serves as a legally binding guideline for forestry.
In the context of NaiS, for each natural hazard a minimal profile of forest properties is described that are required to warrant the protective function. In the case of rockfall, this profile is determined using an app. Depending on the properties of the rocks, slope, tree species composition, and tree size distribution, the external pageapp identifies values of the minimum and ideal sustainable basal area as well as the corresponding stem size distribution.
To do so, stand basal area is distributed evenly over all stem diameter classes to calculate the number of trees per stem diameter class. This assumption tends to lead to unrealistic specifications for the number of trees particularly in the lower stem diameter classes. Since the distributions of stand basal area vary strongly in time and space, it is challenging to derive generally valid, sustainable, and realistic stem number distributions.
An opportunity to contribute to tackling this complex issue is the use of dynamic forest models. They allow for flexibly considering both site-specific environmental factors and management regimes. They also enable simulating forest dynamics and thus the development of forest structure (e.g., stem size distribution, tree species composition) over long periods.
Based on a successful pilot study for the upper montane elevation zone, in this project we use the forest gap model ForClim, which we have successfully developed for more than 20 years at ETH Zurich in the Chair of Forest Ecology. The objectives of this project are:
- To derive sustainably achievable distributions of basal area over all stem diameter classes. Therefore, we consider different management regimes but also numerous forest stands in multiple elevation zones including the sub-montane, upper-montane, high-montane, and sub-alpine;
- To carefully validate the forest model ForClim for these elevation zones on the basis of Growth-And-Yield data from WSL test plots (Experimental Forest Management) to obtain reliable and robust results that can be incorporated into NaiS.
Funding and project patners
Swiss Federal Office for the Environment - external pageBAFU funds the project as part of the currently ongoing revision of the Swiss Forest Management Policy "Sustainability in Protection Forests" (“Nachhaltigkeit im Schutzwald”, external pageNaiS). An important partner of the project is external pageDr. David Forrester (Experimental Forest Management, external pageWSL).
Status of the project
The project runs from September 2020 to August 2021.
Contact
Please contact Ulrike Hiltner for more information.
Harald Bugmann supervises the project.