In Europe, forest ecosystems are facing increasing disturbances such as wildfires, insect-outbreaks and windthrows, and the impacts of such events are likely to increase under ongoing climate change. Increasing disturbances can challenge forest resilience and vulnerability, resulting in higher risks of losing forest ecosystem services. However, quantifying risk across large spatial scales such as Europe is still a fundamental research challenge, since it requires understanding and evaluating the main elements of risk. In this study, we aim to assess the risk of losing forest ecosystem services due to the most common forest disturbances in Europe (wildfires, windthrows and insect-outbreaks – mainly spruce bark beetle). To do so, we mapped the risk components across European forests: exposed values, hazard magnitude, susceptibility and lack of adaptive capacity. Exposed values were quantified in terms of the ecosystem services provided by forests (i.e., timber volume, carbon stocks, soil erosion control, protection against gravitational hazards, and outdoor recreation), that could be lost if the disturbance occurs. The magnitude of the hazard and its probability distribution was quantified using integrative hazard indices (e.g., the Fire Weather Index for wildfires). Susceptibility was based on characteristics that modulate the immediate impacts of the hazard, such as tree height for windthrows or forest continuity for spruce bark beetle. Lack of adaptive capacity was assessed using historical post-disturbance canopy recovery of forests. We integrated and harmonized different indicators, datasets and maps for each risk component and disturbance. Then, we combined the risk components to obtain a risk map for each ecosystem service and disturbance considered, which allowed us to identify the areas with the highest risk. This study is the first ecosystem services’ risk assessment of European forests, which provides critical spatial information for these forests. Given that climate change could amplify forest disturbances, the results of this study could be used to anticipate and adapt to future conditions, as well as to guide efficient forest management.

How to cite: Lecina-Diaz, J., Senf, C., Grünig, M., and Seidl, R.: Ecosystem services at risk from disturbances in European forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5182, https://doi.org/10.5194/egusphere-egu23-5182, 2023.

How to cite: Lam, W. Y. and Mitchell, C.: Cumulative Effects of Beaver Ponds and Forest Harvest on Streamwater Chemistry in Boreal Watersheds , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8928, https://doi.org/10.5194/egusphere-egu23-8928, 2023.

The organization and function of forest ecosystems is changing at an unprecedent rate under the influence of external drivers, such as climate change and human uses. In this context of change, the increasing frequency, intensity and duration of droughts that affect the Mediterranean basin urges to evaluate forest vulnerability to drought and their effects for the long-term stability of these ecosystems. In this study, we explore the responses and factors that control the resilience of holm oak (Quercus ilex) woodlands to recent extreme droughts during 2000-2019, using a remote sensing approach over a broad scale climate aridity gradient that extends from sub-humid to semi-arid climate conditions over 100,000 km² in eastern Spain. Overall, our results indicated that climate aridity and forest structure largely control the resistance, recovery and resilience of the studied holm oak woodlands to drought, which are also affected by drought intensity and both pre- and post-drought hydric conditions. We found that Q. ilex woodlands located in the dry edge of the explored climate aridity gradient showed a high sensitivity to extreme drought. Their resistance, assessed as the capacity of the woodlands to maintain primary production during drought, was low. They also showed a poor resilience, characterized by a low capacity to fully recover their pre-drought production levels. Contrarily, holm oak woodlands in sub-humid areas of the study region, where wetter climate conditions may alleviate water stress during dry periods, showed a high resistance and resilience to the effects of droughts. Drought vulnerability was particularly high for dense holm oak stands developed under semi-arid climate conditions, where strong competition for scarce water resources largely increased the negative effects of extreme drought on landscape-level ecosystem production. We also discuss the implications of these results for adaptive management of holm oak forests in the present context of climate change.

How to cite: Moreno de las Heras, M., Bochet, E., Vicente-Serrano, S., Espigares, T., Molina, M. J., Monleón, V., Nicolau, J. M., Tormo, J., and García-Fayos, P.: Large-scale remote sensing exploration of the resilience of Iberian holm oak woodlands to extreme droughts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8478, https://doi.org/10.5194/egusphere-egu23-8478, 2023.

Natural disturbances like windthrows or forest fires have an effect on the provision of ecosystem services like timber production, protection from natural hazards or carbon sequestration. After a disturbance, forests release large amounts of carbon and therefore change their status from carbon sinks to carbon source. However, forest management may improve the forest capacity to absorb carbon by decreasing the vulnerability to disturbances. In this study we used simulation tools ForestGALES (windthrow) and FlamMap (forest fire) to model the vulnerability to the two disturbances. We analysed forest stands prone to windthrow (in the Carnic Alps) and forest fire (in the Apennines) and proposed forest management in the most vulnerable forest stands, increasing their resistance to the respective disturbance. We simulated the future carbon stock and sink under two scenarios: (1) business-as-usual management, and (2) forest improved using climate-smart forest management to decrease the vulnerability to disturbances. Forest under business-as-usual management led to a decrease in total carbon. Using climate-smart management compared to business-as-usual resulted to an increase of carbon stocks (with additional increase in case of no disturbance). We showed that using disturbance simulation tools may help in decision making process to analyse the most vulnerable forest stands. In combination with simulations of future scenarios of carbon we may be able to direct the climate-smart forestry.

How to cite: Piazza, N., Nevola, E., and Vacchiano, G.: Climate-smart forest management may decrease vulnerability of forest carbon to disturbances, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3682, https://doi.org/10.5194/egusphere-egu23-3682, 2023.

Windthrows are natural disturbances affecting the structure of forests. Such events are predicted to increase in magnitude and frequency due to climate change. The altered forest structure influences forests’ protection capacity against the release of snow avalanches. Previous studies investigated windthrown forest characteristics and their recovery time in study areas smaller than 10 ha, not accounting for larger spatial scales. In this study, we developed a new method for the spatial assessment and monitoring of forests affected by large-scale windstorms to evaluate the protection against the release of snow avalanches. We propose the use of two indices: (1) stored volume height, assessing the uniformity of the biomass on the ground, and (2) adapted tree parameters, evaluating the characteristics of the standing trees. We implemented the algorithm in the R environment and published the scripts on https://github.com/TommBagg/Wind-disturbed_forest_analysis.

The developed indices were applied in two unmanaged windthrow areas periodically surveyed with photogrammetric techniques (deriving dense point clouds) to investigate the long-term changes in protective effects (Disentis, Switzerland) and the short-term influence of snow cover (Franza, Italy). The first area was affected by the storm Vivian in 1990 and four surveys have been performed (1991, 2001, 2009 and 2019), while the storm Vaia hit the Franza area in 2018 and three surveyed were performed (October 2019, October 2020 and December 2020). Analyzing the Disentis area, over 29 years, the minimum level of protective capacity was observed ten years after the storm event. As forest recovery proceeded, forest protective capacity increased again and natural regeneration has progressively provided an anchoring effect against the release of snow avalanches, 29 years after the windthrow event. However, a careful evaluation of the gaps between growing trees (outcome of the adopted tree parameters index) should be performed, as deadwood in these gaps decays, facilitating the potential avalanche formation. The stored volume height was further used to evaluate the forest protection in relation to the snow cover height in the Franza (IT) area, evaluating the necessary snow amount to smooth the rough surface created by the biomass on the ground. This study provided new insights into the long-term protective efficiency of windthrow forests, introducing two new indices to spatially assess and monitor their development over time.

How to cite: Baggio, T., Piazza, N., Bast, A., Bebi, P., and D'Agostino, V.: Novel indices for analysis of protection against snow avalanches in wind-disturbed forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13264, https://doi.org/10.5194/egusphere-egu23-13264, 2023.

Canopy gaps are the fingerprint of forest disturbances, with forest disturbances being the driving force of forest dynamics. Forest gaps can substantially vary in size, from small groups of trees to several hundreds to thousands of hectares being disturbed by windthrow, outbreaks of tree-killing insects or fire. Gap creation is a complex process, because individual disturbance agents can interact, eventually forming larger gaps from linked disturbance events. We still know little about the emergence of gaps: I.e., do small gaps beget large gaps by continuously growing larger, or are small gaps staying small, and large gaps are created large? Furthermore, in order to understand the effect of gaps on forest dynamics, it is equally important to consider gap closure, as the interplay between gap creation and closure determines how persistent gaps are. To address these issues, we here investigated natural patterns of canopy gap creation and closure in an unmanaged temperate mountain forest ecosystem in the Berchtesgaden National Park. Three repeated lidar acquisitions from 2009, 2017 and 2021, covering 3543 ha of closed forest enabled the analysis of gap creation, pervasiveness and closure rates. We delineated gaps from lidar derived Canopy Height Models by thresholding vegetation < 5m and applying a minimum gap size of 400 m² (i.e., approximately the size of one large canopy tree). The identification of gap creation, expansion and closure was done by subtracting each year’s individual gap layers. New and expanding gaps were classified by the presence of gaps in the same geographical location in the previous time step. Crown plasticity leading to lateral closure of gaps vs. ingrowth of regenerating trees are differentiated by the distance to the forest edge and a maximum vertical vegetation height gain during the respective observation period. First results indicate a higher annual gap closure rate (0.66% per year) than annual gap creation rate (0.38% per year), reducing the total gap area across the study area from 22.8% in 2009 to 19.1% in 2021. With increasing elevation, both gap creation and closure increase. Gap expansion is the dominant process of gap creation, underlining the spatially contagious nature of the dominant disturbance agents in the area, such as bark beetles and windthrow. Wind creates edges, which are again more susceptible to wind and provide abundant breeding material for bark beetles that can infest neighboring stands, again creating edges susceptible to wind. Regeneration is the dominating process of gap closure, while lateral crown expansion plays a crucial role mainly in broadleaved forests dominated by European beech. Smaller gaps close disproportionally faster than larger gaps and mixed forests close gaps faster than pure forests, likely due to niche complementarity. Overall, our study presents the first landscape-scale assessment of canopy gap creation and closure in temperate mountain forests and adds to our understanding of forest dynamics.

How to cite: Krüger, K., Pflugmacher, D., Senf, C., Jucker, T., and Seidl, R.: Canopy gap creation and closure in temperate mountain forests identified from multi-temporal lidar data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13775, https://doi.org/10.5194/egusphere-egu23-13775, 2023.

Wildfire is a natural disturbance in the Iberian Range, often caused by lightning. After the 7,600 ha fire in the Cuencas Mineras de Teruel region in 2009, a restoration project is being carried out on 1,234 ha with the aim of developing a forest adapted to challenges as a) new climate scenario; b) future fires; c) wild ungulate expansion/livestock management. Four ecosystem services have been prioritized: water supply, carbon storage, livestock feeding, and biodiversity.

Forest recovery has been promoted by means of plantations as well as spontaneous revegetation (26% and 11,5% respectively of the pre-fire forest surface). Plantation has been made in scattered stands in order to create fire discontinuity. Trees density has been lowered (750-1.100 trees/ha) to reduce fuel in the forest and increase water availability per tree. Resprouting and seeding species have been introduced. Pinus halepensis has been planted above 1,000 m of altitude because conditions are getting drier and warmer. Since 2014 71,75 ha have been planted with a survival rate of around 63,5%. The least successful species has been Pinus sylvestris (50% on average) with the lowest records in sunny exposures and convex landforms due to the new climatic scenario. The sustainable stocking density has been estimated at 700 ewes to promote livestock activity. In order to enhance the sheep flock activity a livestock pen has been built that allows the grazing season to be extended over time. We assume that in planted stands, rainwater will be consumed by the vegetation (evapotranspiration: green water). In non-planted areas, livestock activity is encouraged, thus acting as firebreaks and as producers of blue water, since part of the rainwater will recharge aquifers and watercourses.

Biodiversity results favored by spontaneous revegetation as well as by the protection of the Natura 2000 habitat 6210 “Semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia)”, which has not been planted. In practice, a mosaic landscape has been constructed.

The water supply (blue/green water ratio) has been estimated by applying Zhang's hydrological model.  Barandica and Berzosa model was used for carbon storage estimation. Four scenarios have been considered: a) traditional land uses before rural depopulation (the year 1956); b) pre-fire landscape (the year 2009); c) post-fire landscape (the year 2012); d) restored forest (the year 2050). Results show an increase of about 4,5% in water supply and a decrease of about 40% in carbon storage when comparing the pre-fire scenario with the restored forest. An integrative approach including the management of water, carbon, livestock, and biodiversity is necessary in order to develop mosaic landscapes resilient to the main disturbances in the Mediterranean-continental environments.

How to cite: Nicolau Ibarra, J. M. and Reiné, R.: Mosaic landscape restoration after wildfire under Mediterranean-continental conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16997, https://doi.org/10.5194/egusphere-egu23-16997, 2023.

Within the forested karstic alpine water protection zones of various water suppliers in Austria like e.g. those of the Cities of Vienna and Waidhofen/Ybbs, strong precipitation events have triggered erosion processes in ditch sites, causing forest decline and turbidity in the related karstic aquifers. Both processes are intended to be mitigated or avoided, as forest cover and water supply are negatively influenced by these natural disturbances. As response strategy an outstanding precipitation event from the year 2013 on Mount Rax was analyzed both on the level of (A) the meteorological characteristics of this event and (B) it’s impacts on ditch sites and forest cover within the part of the water protection zone affected by this rainfall event (WPZ).

The meteorological characteristics of the event from 9^th of August 2013 define it as outstanding strong precipitation event, yielding 79,2 mm of rainfall within the first 2 hours and 119,2 mm within the whole event (10 hours). It was a thunderstorm event including hail, which became visible by soil temperature analysis. The inclusion of hail lowered the temperature of the water moving in and on the forest soils, by the way increasing its erosive potential through boosting its drag force for any given substances, in our context soil materials. The data stem from high temporal resolution hydro-meteorological stations (10 minutes measurement interval) within the WPZ. The precipitation event caused major impacts on ditch sites, like deep v-notch erosion or erosion of the upper soil substances and forest roads.

Therefore, the ditch sites within the WPZ were analyzed both through interpretation of aerial orthophotos and a field mapping survey leading to the GIS-based processing of the yielded data. It was possible to show that especially ditch sites beneath rock areas showed strong erosion dynamics affecting both forest vegetation cover and soil substances. Deep v-notch erosion occurred in such ditch types. Also totally new ditch sites were created through the analyzed event. In the course of the mapping survey, the soil type, vegetation cover and percentage of the site affected through erosion processes were analyzed.

The only chance to mitigate the impacts of the natural disturbance category “outstanding strong precipitation events” is a stable, vital and dense vegetation cover on ditch sites, including both ground vegetation and tree cover. Especially stable tree species like Sycamore Maple (Acer pseudoplatanus) or European larch (Larix decidua) can facilitate the stability of vegetation cover on ditch sites. The mitigation of the erosion processes has positive effects on forest cover, and above all, on water supply systems, as increased turbidity is one of the main causes for water quality issues in karstic alpine watersheds. Because of this fact it is necessary to avoid processes which damage the natural regeneration dynamics of forest ecosystems, like e.g. browsing damages on tree species. Strategical efforts of forest management have to focus on the stabilization of vegetation cover on such ditch sites. Those are supported through the Forest Hydrotope Model (a forest site model) data base which was elaborated for the WPZ.

How to cite: Koeck, R., Suppan, F., and Hochbichler, E.: Ditch Erosion Processes triggered through Strong Precipitation Events: Implications for Forest Ecosystem Stability and Water Resources Protection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15197, https://doi.org/10.5194/egusphere-egu23-15197, 2023.