Economic valuation of ecosystem-based rockfall risk reduction considering disturbances and comparison to structural measures

Quantifying the resistance of mixed-forests against natural hazards in the Pyrenees

Mountain protection forests can prevent natural hazards by reducing their onset and propagation probabilities. In fact, individual trees act as natural barriers against hydrogeomorphic events. However, assessing the structural strength of trees against these hazards is challenging, especially in a context of climate change due to the intensification of extreme events and changes in forest dynamics. Here, we focus on the mechanical analyses of two of the most common tree species across the Pyrenees (Abies alba Mill. and Fagus sylvatica L.) growing in two different areas (Spain and France), and affected by recurrent snow avalanche and rockfall events. We first performed 53 pulling test on mature trees, where the root-plate stiffness and the modulus of elasticity of the stems were evaluated. To further analyse the impact of forest management and climate on protective forests, we yielded information on tree growth using dendroecology techniques. Then, we assessed structure and neighbourhood characteristics for each target tree to account for the surrounding forest structure. Finally, using linear and structured equation models we tested if the mechanical capacity of the trees is determined either by functional traits (e.g. species, tree growth, diameter and height) or forest structural traits (e.g. tree density, tree structure and slenderness) or both. Our results suggest that the forest neighbourhood influences tree mechanical capacity through two pathways, including both functional and structural traits. The individual stiffness parameter of trees is influenced by their functional traits, while their structural traits are more closely related with changes in the modulus of elasticity. Both species exhibit varying levels of dominance in different locations, which is related to their resilience to the diverse natural hazards they confront. Our findings provide relevant insights to anticipating management strategies for forests that serve as a protective barrier against natural hazards in the context of a changing climate.

Mapping the natural disturbance risk to protective forests across the European Alps

Mountain forests play an essential role in protecting people and infrastructure from natural hazards. However, forests are currently experiencing an increasing rate of natural disturbances (including windthrows, bark beetle outbreaks and forest fires) that may jeopardize their capacity to provide this ecosystem service in the future. Here, we mapped the risk to forests' protective service across the European Alps by integrating the risk components of hazard (in this case, the probability of a disturbance occurring), exposure (the proportion of forests that protect people or infrastructure), and vulnerability (the probability that the forests lose their protective structure after a disturbance). We combined satellite-based data on forest disturbances from 1986 to 2020 with data on key forest structural characteristics (cover and height) from spaceborne lidar (GEDI), and used ensemble models to predict disturbance probabilities and post-disturbance forest structure based on topographic and climatic predictors. Wind and bark beetles are dominant natural disturbance agents in the Alps, with a mean annual probability of occurrence of 0.05%, while forest fires were less likely (mean annual probability <0.01%), except in the south-western Alps. After a disturbance, over 40% of forests maintained their protective structure, highlighting the important role of residual living or dead trees. Within 30 years after wind and bark beetle disturbance, 61% of forests were likely to either maintain or recover their protective structure. Vulnerability to fires was higher, with 51% of forest still lacking sufficient protective structure 30 years after fire. Fire vulnerability was especially pronounced at dry sites, which also had a high fire hazard. Combining hazard and vulnerability with the exposure of protective forests we identified 186 Alpine municipalities with a high risk to protective forests due to wind and bark beetles, and 117 with a high fire risk. Mapping the disturbance risk to ecosystem services can help identify priority areas for increasing preparedness and managing forests towards lower susceptibility under an intensifying disturbance regime.

Biological Legacies and Rockfall: The Protective Effect of a Windthrown Forest

Windstorms represent one of the main large-scale disturbances that shape the European landscape and influence its forest structure, so post-event restoration activities start to gain a major role in mountainous forest management. After a disturbance event, biological legacies may enhance or maintain multiple ecosystem services of mountain forests such as protection against natural hazards, biodiversity conservation, or erosion mitigation. However, the conservation of all these ecosystem services after stand-replacing events could go against traditional management practices, such as salvage logging. Thus far, the impact of salvage logging and removal of biological legacies on the protective function of mountain stands has been poorly studied. Structural biological legacies may provide protection for natural regeneration and may also increase the terrain roughness providing a shielding effect against gravitational hazards like rockfall. The aim of this project is to understand the dynamics of post-windthrow recovery processes and to investigate how biological legacies affect the multifunctionality of mountain forests, in particular the protective function. To observe the role of biological legacies we performed 3000 simulations of rockfall activity on windthrown areas. Results show the active role of biological legacies in preventing gravitational hazards, providing a barrier effect and an energy reduction effect on rockfall activity. To conclude, we underline how forest management should take into consideration the protective function of structural legacies. A suggestion is to avoid salvage logging in order to maintain the multifunctionality of damaged stands during the recovery process.

From ecosystems to socio-economic benefits: A systematic review of coastal ecosystem services in the Baltic Sea

Seagrass meadows, algal forests and mussel beds are widely regarded as foundation species that support communities providing valuable ecosystem services in many coastal regions; however, quantitative evidence of the relationship is scarce. Using the Baltic Sea as a case study, a region of significant socio-economic importance in the northern hemisphere, we systematically synthesized the primary literature and summarized the current knowledge on ecosystem services derived from seagrass, macroalgae, and mussels (see animated video summary of the manuscript: Video abstract). We found 1740 individual ecosystem service records (ESR), 61% of which were related to macroalgae, 26% to mussel beds and 13% to seagrass meadows. The most frequently reported ecosystem services were raw material (533 ESR), habitat provision (262 ESR) and regulation of pollutants (215 ESR). Toxins (356 ESR) and nutrients (302 ESR) were the most well-documented pressures to services provided by coastal ecosystems. Next, we assessed the current state of knowledge as well as knowledge transfer of ecosystem services to policies through natural, social, human and economic dimensions, using a systematic scoring tool, the Eco-GAME matrix. We found good quantitative information about how ecosystems generated the service but almost no knowledge of how they translate into socio-economic benefits (8 out of 657 papers, 1.2%). While we are aware that research on Baltic Sea socio-economic benefits does exist, the link with ecosystems providing the service is mostly missing. To close this knowledge gap, we need a better analytical framework that is capable of directly linking existing quantitative information about ecosystem service generation with human benefit.

Rockfall Research: A Bibliometric Analysis and Future Trends

Rockfall is one of the main phenomena in mountainous environments due to its fast and high speed of movement, its unpredictability, and, therefore, the difficulty of identifying signs of instability and detachment of the blocks. Compared to other types of sliding, the proportion of rockfall research is smaller and sometimes little known, but, in the last five years, rapid growth in this area has been shown. Therefore, this research aimed to review the intellectual structure of rockfall, through analysis of scientific production using bibliometric techniques that allow its analysis, knowledge, global evolution, and future trends in rockfall. The research methodology consists of three steps: (1) data compilation, (2) software and data cleaning, and (3) analysis, interpretation, and visualization. This analysis focuses on the period from 1975 to 2019. For the data, a total of 811 academic publications were retrieved from the Scopus database. The results indicate an increasing trend of annual publications on rockfall. This analysis reveals the main topics, countries, and most influential institutions in the world that have carried out relevant research in scientific publications; it also shows the journals that have the most publications. VOSviewer software was adopted to evaluate the co-occurrence of author keywords. Currently, the hotspots rockfall issues mainly include: hazard-risk assessment, remote sensing, and rockfall monitoring. Finally, this article analyzes the limitations of current research and proposes a future direction for the development of new research.