Mountain forests significantly contribute to the habitability of mountain regions, reducing risk for people, infrastructure and resources suffering from natural hazards, including floods, debris floods, debris flows, snow avalanches and rockfalls. Mountain forests are, however, also highly sensitive to climate variability, potentially eroding their protection function under climate change. Since the 19th century, European and other countries in mountain regions have developed a variety of forest and landscape managing techniques for sustaining the protective function of forests. Those management techniques can be seen as are part of the European natural and technical heritage and are of high public interest. Yet, natural disturbances, changes in forest structure and biodiversity, and regeneration failure might pose substantial challenges to forest and landscape management. We thus need to increase our understanding of how the protective function of mountain forests is affected by climate change. The aim of the session consequently is to compile current knowledge on climate change impacts on mountain forests ecosystems and their protective function against natural hazards across the globe.
Potential topics might include the monitoring and modelling of changing disturbance regimes and their impacts on the protective functions of forests, regeneration and recovery failure of mountain forests, and the effects of human land use and changing societal demands on mountain forests and their protective forests. We hope to gain a broad overview on global mountain forest ecosystems in the context of protection against natural hazards.

Convener: Christian Scheidl | Co-conveners: Cornelius Senf, Michaela Teich, Micha Heiser, Julius Sebald
| Attendance Fri, 08 May, 14:00–15:45 (CEST)

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Chat time: Friday, 8 May 2020, 14:00–15:45

Chairperson: Scheidl
D539 |
Oles Ridush, Bogdan Ridush, and Daria Kholiavchuk

The goal of our research is to forecast the possible avalanches in the zones of active deforestation, especially situated close to the infrastructure objects and settlements.
Despite the fact, that in Ukrainian Carpathians snow avalanches were observed by the Ukrainian Hydrometeorological Service, some recent events showed us, that it does not fulfill the current situation. The observations are regularly held in alpine and subalpine zones (>1300m. a.s.l.) of mountain ranges, in the same time territories with lower altitudes were not studied.
Due to the active deforestation of the region in recent years, it appeared in new territories with conditions suitable for the appearance of avalanches. Because deforestation is mainly held on territories with lower altitudes, which are often densely settled, it makes such avalanches hazardous for the infrastructure and settlements. One of such avalanches occurred on the slope near village Kruhlyi (Rakhiv District, Zakarpatska oblast') in February 2019, that caused blocking of the international highway with 300 m3 of ice and snow. The avalanche occurred on the deforested area with altitudes between 400 and 480 m a.s.l., inclination around 28⁰ and 150m long. This event changes our vision in avalanche expectancy in the Carpathian Mountains to much lower altitudes. Research is currently being held based on data about deforestation and detecting areas with suitable avalanche properties.
This research was supported by the project “Snow-avalanche activity from Romanian and Ukrainian Eastern Carpathians”, funded by AUF and IFA Romania.

How to cite: Ridush, O., Ridush, B., and Kholiavchuk, D.: Avalanche hazard in low-mountain part of Eastern Carpathians, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-879, https://doi.org/10.5194/egusphere-egu2020-879, 2020.

D540 |
Àngela Manrique-Alba and Santiago Beguería

Temperatures have increased worldwide in the last decades, with the most pronounced and rapid changes occurring at high altitudes and latitudes. Climate change has played an important role in modifying the altitudinal location of the treeline ecotone, i.e. the transition from timber line (the upper forest limit, defined by the presence of a continuous forest cover) to the treeline (the last upright trees reaching 2 or 3 m in height). Moreover, the influence of recent land use change (e.g., changes in pastoral use, tourism development) in treeline dynamics is increasingly acknowledged. We have compiled a dataset of treeline changes over the Pyrenees mountain range, extending over more than 12000 linear kilometres, representing a large study area that extends across a broad range of environmental conditions. The main objective was to assess the effects of climate change, past land uses and physiography on the treeline dynamics between 1956 and 2015. To explore the variation in treeline shifts we used pairs of aerial photographs taken in 1956 and 2015 and we identified the position of the tree line using a criterion based on canopy cover thresholds. Our findings show significant differences between tree line dynamics for the two analysed periods and allow us to infer the relative importance of climatic factors, land use change, and local anthropogenic influence modulating the treeline structure and its dynamics.

How to cite: Manrique-Alba, À. and Beguería, S.: What explains the elevational upward shifts at the treeline ecotone?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9284, https://doi.org/10.5194/egusphere-egu2020-9284, 2020.

D541 |
Nuria Guerrero-Hue, Michaela Teich, Kurt Nicolussi, Thomas Pichler, Marc Adams, Christian Scheidl, and Jan-Thomas Fischer

Snow avalanches are natural disturbances that can cause substantial damage to forests, and endanger people and material assets. Knowledge of past avalanches is crucial for forest management and planning technical mitigation measures. Dendrogeomorphology can provide information on previous disturbances, for example tree damages, caused by avalanches in forested terrain. By analysing the past growth of trees, both temporal and spatial reconstructions of the avalanche activity in forests are possible.

We use a dendrogeomorphological approach to study the past avalanche activity on an avalanche path above the city of Innsbruck in Austria. The area is of high importance for recreation (e.g. hiking, biking and skiing) as well as avalanche mitigation. Protection forest and technical protection measures are already in place (breaking mounds, catching and deflection dams) and frequently interact with avalanches. In January 2019, an avalanche with a destructive size of 3 - 4 released above the Arzler Alm mountain hut and caused considerable damage to approx. 25 ha of forest. This event provided us with the opportunity to conduct the present study. We sampled 104 trees along three longitudinal transects at elevation bands of 1200, 1100 and 1000 m a.s.l. covering the damaged area. We furthermore applied a selective sampling scheme below the forest damage along a gully where avalanches that reached the city of Innsbruck had previously been observed. Using an increment borer at least two cores per tree were taken from damaged and undisturbed trees. A mixture of conifers and broadleaved trees (mostly Picea abies (L.) Karst, Fagus sylvatica L. and Abies alba Mill.), as well as old and young trees was selected. In addition, we recorded the exact position of each tree and measured several tree parameters (e.g. diameter at breast height, tree height, damage description). Each core was then prepared following a standard dendrochronological procedure. Tree-rings were counted and ring-width was measured using a stereo microscope and a time-series analysis program (TSAP Win). Additionally, a visual detection of growth reactions (traumatic resin ducts, reaction wood, scars, callus tissue, growth suppression or releases) was performed, and tree-ring series were cross-dated and compared with local reference chronologies. Years with tree-rings showing growth anomalies potentially caused by ecological or climatic factors were discarded as possible avalanche years.

Going forward we will compare years with major avalanche events identified by the dendrogeomorphological analysis, with existing extensive archival data and orthophotos. We expect this to confirm known events, but also to provide new information on unknown events.  Based on the location of sampled trees, we will furthermore reconstruct the spatial extent of past events to estimate magnitude and frequency of avalanche activity in the area. Our results will also contribute to better predicting size and periodicity of future avalanche events and revealing potential changes in the avalanche regime. This in turn is relevant to calibrating and validating avalanche simulation models as well as for the design of technical and silvicultural protection and mitigation measures, which is especially important for an Alpine city like Innsbruck.

How to cite: Guerrero-Hue, N., Teich, M., Nicolussi, K., Pichler, T., Adams, M., Scheidl, C., and Fischer, J.-T.: Snow avalanche activity above Innsbruck, Austria: a dendrogeomorphological approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10058, https://doi.org/10.5194/egusphere-egu2020-10058, 2020.

D542 |
Moonil Kim, Nick Strigul, Elena Rovenskaya, Florian Kraxner, and Woo-Kyun Lee

The velocity and impact of climate change on forest appear to be site, environment, and tree species-specific. The primary objective of this research is to assess the changes in productivity of major temperate tree species in South Korea using terrestrial inventory and satellite remote sensing data. The area covered by each tree species was further categorized into either lowland forest (LLF) or high mountain forest (HMF) and investigated. We used the repeated Korean national forest inventory (NFI) data to calculate a stand-level annual increment (SAI). We then compared the SAI, a ground-based productivity measure, to MODIS net primary productivity (NPP) as a measure of productivity based on satellite imagery. In addition, the growth index of each increment core, which eliminated the effect of tree age on radial growth, was derived as an indicator of the variation of productivity by tree species over the past four decades. Based on these steps, we understand the species- and elevation-dependent dynamics. The secondary objective is to predict the forest dynamics under climate change using the Perfect Plasticity Approximation with Simple Biogeochemistry (PPA-SiBGC) model. The PPA-SiBGC is an analytically tractable model of forest dynamics, defined in terms of parameters for individual trees, including allometry, growth, and mortality. We estimated these parameters for the major species by using NFI and increment core data. We predicted forest dynamics using the following time-series metrics: Net ecosystem exchange, aboveground biomass, belowground biomass, C, N, soil respiration, and relative abundance. We then focus on comparing the impact of climate change on LLF and HMF. The results of our study can be used to develop climate-smart forest management strategies to ensure that both LLF and HMF continue to be resilient and continue to provide a wide range of ecosystem services in the Eastern Asian region.

How to cite: Kim, M., Strigul, N., Rovenskaya, E., Kraxner, F., and Lee, W.-K.: Understanding and predicting species- and elevation-dependent dynamics in East Asian temperate forests , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20968, https://doi.org/10.5194/egusphere-egu2020-20968, 2020.

D543 |
Ana Stritih, Peter Bebi, and Adrienne Grêt-Regamey

For centuries, mountain forests in the Alps have provided essential ecosystem services such as wood production and protection from natural hazards (e.g. avalanches and landslides), which enable mountain societies to thrive in these marginal environments. These ecosystem services are affected by climate and land use change, as well as changes in societal demand and management regimes. In recent years, the management of mountain forests has been increasingly driven by forest disturbances, such as windthrow, bark beetle outbreaks, and forest fires. The increasing rate of disturbances has the potential to convert forests from carbon sinks to carbon sources, and may also affect the provision of other ecosystem services, such as avalanche protection. The capacity of forests to provide services, their vulnerability to disturbance, and their resilience depend on their structure, composition and management regime. Forests with a heterogeneous structure and species composition are expected to better maintain their protection function after disturbances.

Information on forest structure and its link to functions and services is available from a variety of sources, from Earth Observation and in-situ data, existing process-based models, to local expert knowledge. We use Bayesian Networks to integrate these different types of information and model ecosystem services (carbon sequestration, wood production, and avalanche protection) in the Swiss Alps. This probabilistic modelling approach allows us to identify knowledge gaps and explore uncertainties in the future provision of ecosystem services. Since disturbances are a major source of uncertainty, we combine remote sensing and forest management data to investigate how disturbance severity and post-disturbance recovery are influenced by stand characteristics, such as structural heterogeneity. Based on this analysis, we discuss how forest management can help ensure the provision of mountain forest ecosystem services under changing disturbance regimes. 

How to cite: Stritih, A., Bebi, P., and Grêt-Regamey, A.: Mountain forest ecosystem services – maintaining resilience in the face of disturbances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21291, https://doi.org/10.5194/egusphere-egu2020-21291, 2020.

D544 |
Marco Maneta, Solomon Dobrowski, Zack Holden, Anna Sala, Gerard Sapes, and Caelan Simeone

More frequent hydrologic stress events associated with increasing air temperatures and declining precipitation in the western U.S are resulting in more frequent and larger forest fires and tree die offs. It is also producing drier and hotter soils that are gradually becoming inadequate for seedlings, reducing the probability of recruitment and forest recovery and increasing the probability of permanent forest loss.

We use a spatially-distributed ecohydrologic model (Ech2o-SPAC) to simulate the spatial distribution of soil moisture and the conditions that generate water stress in plants at high resolution and regional extents. The model represents water stress in seedlings from a mechanistic point of view by simulating the water potential within the vascular system of seedlings. When the water potential within seedlings is very low, cavitation events that reduce water transport in the hydraulic column occur, which generate hydraulic stress. Time series of cavitation-induced low hydraulic conductivity events are combined into an index that integrates their intensity, duration and frequency to generate a dynamic stress index. The spatially distributed nature of the model permits to obtain maps of the dynamic stress index that can be directly related to the probability of seedling mortality and its influence on the regeneration potential of the lower treeline.

The model was calibrated for Pinus ponderosa seedlings using a glasshouse drought experiment and was tested using in situ monitoring data on seedling mortality from reforestation efforts. The calibrated model was used to simulate water-induced stress and mortality in seedlings in western Montana. Results show that low elevation, south facing, non-convergent topographic locations with high atmospheric demand and limited upslope water subsidies experienced the highest rates of modeled mortality. Furthermore, modeled drought mortality in seedlings from 2001-2015 correlated with the current distribution of forest cover near the lower treeline suggest that drought limits recruitment and ultimately constrains the low elevation extent of conifer forests within the region. Extrapolation of the results show that many low elevation forest regions in the western US may have crossed climatic thresholds that prevent recruitment and will probably not recover after disturbance.

How to cite: Maneta, M., Dobrowski, S., Holden, Z., Sala, A., Sapes, G., and Simeone, C.: Hydrologic stress suppresses tree regeneration and destabilizes the lower treeline in the U.S. Rocky Mountains , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21835, https://doi.org/10.5194/egusphere-egu2020-21835, 2020.

D545 |
Maximilian Rossmann, Michael Schiffer, and Christian Scheidl

The Bannwald Hallstatt in the Upper Austrian Salzkammergut, is one of the oldest measures to protect the people, the settlement area, the energy supply of the community Hallstatt, as well as important infrastructure facilities in the region. In particular, the Hallstatt World Cultural Heritage Site with its settlements and access roads, which is strongly influenced by tourism, is protected.

A new project planned for 2020 will extend the area of the Bannwald forest, which has existed since 1879, in a south-westerly direction, thus protecting the permanent settlement area of the Echerntal Valley from gravitational natural hazards. As a result, the project area, which currently covers 270 hectares, will almost double to 489 hectares. 20 million euros have been budgeted for the implementation of the project, for the next 30 years. In order to be able to use these funds in an optimal and targeted manner, it is extremely important to know the protection performance of the existing forest. In the present study a model was developed to show the protective effect against rockfall and avalanches. For this purpose, an evaluation matrix with differently weighted influencing variables was developed, which was presented as a thematic map in the form of a traffic light system ("ideal"/green, "minimal"/orange, "not fulfilled"/red.). In order to be able to better illustrate the tendencies of the achieved protection effect, a “protective-forestometer” was developed. This visualizes the protection performance of the observed partial area with a pointer and a percentage indication.

However, the aim of this work was to derive the protective performance of the individual forest areas from a purely economically oriented forest management system. Hence, the data basis for this work was the 2017 forest inventory of the Austrian Federal Forestry Company (Österreichische Bundesforste AG).

How to cite: Rossmann, M., Schiffer, M., and Scheidl, C.: The influence of canopy disturbances on landslide susceptibility in mountain forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22103, https://doi.org/10.5194/egusphere-egu2020-22103, 2020.

D546 |
Markus Beck and Johannes Hübl

Large wood can cause serious damage on existing structures like bridges, dams and flood protection measures. Therefore, large wood recruitment in rivers became an important topic concerning risk mitigation and flood protection both in mountainous areas and in lowland rivers all around the world. However, former mitigation constructions like check dams, often don’t consider the impact of single wood pieces or the effect of a dense wood accumulation on the stability and function. To avoid potential negative effects, several strategies have been established. An often-used strategy is to filter out the wood pieces before a critical river section or structure is affected.


In the year 2002, a flood event in the Naarn river in Perg, Austria, mobilized and transported large wood pieces along the river path and caused damage at a bridge in the downstream settlement area. The mobilization was mainly caused by side erosion along the wooded hillslopes connected to the river system. To avoid this problem in future, a protection measure to filter out large wood is planned in the above situated river section. To estimate the effect of the planned measure, different scenarios will be analyzed, based on a small scale hydraulic physical model with compliance to Froude scaling. The research focus lies on the effectivity of the measure with a discharge ranging from a frequent (one-year recurrence) discharge event (HQ1) to a design event of a 100 year recurrence discharge (HQ100) as well as the case of a system overload. Forces, flow velocity and flow depths and the effect of debris accumulation are also part of the research. The main goal is to find the optimal filter structure with the highest effectivity. The results of this model will be realized at the Naarn river.

How to cite: Beck, M. and Hübl, J.: Filtering of large wood in torrential catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22538, https://doi.org/10.5194/egusphere-egu2020-22538, 2020.