Protective Forests for Ecosystem-based Disaster Risk Reduction (Eco-DRR) in the Alpine Space

Abstract

Mountain forests are an efficient Forest-based Solution (FbS) for Ecosystem-based Disaster Risk Reduction (Eco-DRR) by lowering the frequency, magnitude, and/or intensity of natural hazards. Technical protection measures are often poor solutions as stand-alone measures to reduce disaster risk limited by material wear and fatigue or financial resources and aesthetical values. Protective forests should therefore be considered as key elements in integrated risk management strategies. However, the definition of protective forests and the understanding and assessment of their protective functions and effects differ greatly among Alpine Space countries. In this chapter, we present a short introduction to the concept of Eco-DRR and companion terms and propose a definition of FbS as a specific case of Nature-based Solutions for an ecosystem-based and integrated risk management of natural hazards. That is, we guide the reader through the maze of existing definitions and concepts and try to disentangle their meanings. Furthermore, we present an introduction to forest regulations in the Alpine Space and European protective forest management guidelines. Our considerations and recommendations can help strengthen the role of protective forests as FbS in Eco-DRR and the acknowledgment of the key protective function they have and the crucial protective effects they provide in mountain areas.

1. Introduction

The adverse impacts of climate change on societal and environmental systems are serious threats to the habitability and development of mountain areas worldwide by impacting the three components of the risk concept: hazard, vulnerability, and exposure [1]. The negative correlation between climate change impacts and ecosystems’ health and vitality is becoming increasingly evident. Many studies and first-hand accounts have shown that overexploited and/or degraded ecosystems are less resistant to external stressors, leading to disasters caused by more frequent and intense natural hazards of greater magnitude [2, 3]. Given the strong link between climate change adaptation and disaster risk reduction—actions aimed at reducing hazard, vulnerability, and/or exposure—a preventive and integrated risk management (IRM) is essential [4, 5] (see also chapter [6] of this book).

In the era of overpopulated risk-prone areas and settlement expansion into previously uninhabited regions [7, 8], implementing more and bigger technical measures (also called “gray infrastructure”) for protection against natural hazards cannot be the sole answer to the rising disaster risk. Engineers such as Alexandre Surell (1813–1887) and Prosper Demontzey (1831–1898) came to this conclusion as early as the nineteenth century. They used grassing and afforestation of deforested slopes in the Alps to supplement structural measures, protecting against soil erosion, torrential floods, and snow avalanches. Limited by hazard resistance, material wear and fatigue, available space, financial resources, and aesthetical values, gray infrastructure as a stand-alone protection measure is an inadequate solution for risk reduction, especially in rural and nonurban areas [9, 10]. In contrast, Nature-based Solutions (NbS) take advantage of ecosystems and the services they provide to address societal challenges such as climate change, food security, or natural disasters (see Figure 1) [11, 12, 13, 14].

Figure 1.

The concept of Nature-based Solutions (NbS) as defined by the International Union for Conservation of Nature (IUCN). NbS are accompanied by benefits from healthy ecosystems, targeting societal challenges such as climate change, disaster risk reduction, food and water security as well as health and are critical to economic development. Adapted from [15].

Nature-based Solutions are an umbrella term that appeared in the 2000s to overarch all “actions to protect, sustainably manage, and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits,” as defined by the International Union for Conservation of Nature (IUCN; [15]). NbS therefore encompass various established climate change adaptation and disaster risk reduction approaches [13], such as:

• Ecosystem-based Adaptation (EbA) measures, which use biodiversity and ecosystem services as part of an overall strategy to help communities adapt to climate change impacts by, for example, reducing carbon emissions from ecosystem degradation and enhancing carbon sequestration. EbA recognizes the importance of equity and gender and the role of local and traditional knowledge as well as species diversity and the provision of other co-benefits that are crucial for livelihoods and human well-being [16, 17];

• Green infrastructure (GI), a strategically planned network of natural and seminatural areas with environmental features designed and managed to deliver a wide range of ecosystem services, including green spaces and other physical features in terrestrial, coastal, and marine areas [11, 18]; and

• Ecosystem-based Disaster Risk Reduction (Eco-DRR), which is the “sustainable management, conservation and restoration of ecosystems to reduce disaster risk, with the aim to achieve sustainable and resilient development” [4]. Well-managed ecosystems can therefore act as Eco-DRR measures by influencing one or more of the three (natural) hazard components (Figure 2) and by providing additional ecosystem services, which are essential to increase the socio-economic resilience and sustain the livelihoods of people and communities [21, 22]. Therefore, this concept, which first appeared in 2009 and was defined in 2013 [22], fits the objectives and principles of managing forest ecosystems in mountain areas for protecting people and assets against natural hazards, similar to the long-existing concept of multifunctional mountain forest management (e.g., [23]).

Figure 2.

Conceptual framework of the climatic, ecological, economic, and social conditions that influence the risk of gravitational natural hazards in mountain areas resulting from the interaction of a hazard (hazard potential) with exposure and vulnerability (damage potential) of human and natural systems. The effects of forest on the three hazard components frequency (i.e., onset probability), magnitude (i.e., propagation probability), and intensity are highlighted in green. Adapted from [1, 6, 19, 20].

Mountain areas and their inhabitants are particularly vulnerable to climate change while also being exposed to several natural hazards. This requires enhancing mountain communities’ ability to manage the involved risks while being conscious of the tremendous natural capital mountain landscapes provide.

Mountain forests can prevent natural hazards or lower their frequency, magnitude, and/or intensity by reducing onset (release) and/or propagation (runout) probabilities [19, 24, 25, 26]. Making the Alpine Region inhabitable, these so-called protective forests (or protection forests [27]) therefore represent an effective solution for Eco-DRR and should have a key role within the portfolio of IRM measures.

However, actions related to NbS are often not compatible with managing protective forests for the sustainable provision of their protective effects. NbS are applied at landscape scales aiming at simultaneously providing human well-being and biodiversity benefits. In contrast, protective forests as “Forest-based Solutions” (FbS) are a specific case of NbS, which is dedicated to preventing and mitigating natural hazard risks. They are mainly implemented at the slope scale together with spatial planning (hazard zoning) and technical measures as part of an IRM.

Nevertheless, a sustainable management of protective forests to improve their resilience and protective effects generates important co-benefits, such as carbon sequestration and aesthetical values, and supports local communities’ livelihoods [21, 28]. Given the similarities between Eco-DRR and EbA measures, protective forests are an excellent example for no-regret actions, i.e., solutions “that will always have a positive impact on livelihoods and ecosystems regardless of how the climate changes” [29]. Furthermore, a sustainable and risk-based management of protective forests can achieve both disaster risk reduction and climate change adaptation [30, 31]. Nonetheless, the recognition of these forest stands as effective and cost-efficient Eco-DRR measure is still in need of improvement [4]. Despite acknowledging the important functions mountain forests have for the protection against natural hazards since at least the eighteenth century [8], only 60 out of 10,357 peer-reviewed scientific publications published between 1980 and 2019 that address risk management of gravitational natural hazards (snow avalanches, rockfall, shallow landslides, and debris flows) also include “ecosystem-based solutions” (including search terms such as Nature-based Solutions, Eco-DRR, green infrastructure, and protective forest) [32]. However, additional documents were published, for example, by international organizations such as the IUCN, the Food and Agriculture Organization of the United Nations (FAO), and the Partnership for Environment and Disaster Risk Reduction (PEDRR) [4, 22, 29, 33], endorsing the protective function of mountain forests and their inclusion into current natural hazard risk management strategies toward an ecosystem-based and integrated risk management.

The application of IRM in mountain areas makes it possible to incorporate FbS as Eco-DRR measures including protective forests to prevent or mitigate natural hazards, which allows creating resilient landscapes as the overarching goal [4]. Of course, also FbS have limitations, which are still inhibiting their application on large spatial scales. Green infrastructure needs enough space and favorable ecologic conditions to thrive and will degrade, if not properly managed, which leads to a decline in their performances [10, 17]. From a decision-maker perspective, few economic evaluation methods are currently available to compare the cost-effectiveness of green and gray infrastructures [29, 34, 35, 36] (see also chapters [37, 38, 39, 40] of this book). The available methods often lack in accurate performance assessment, long-term effectiveness monitoring, and a definition of environmental, economic, and/or societal impact evaluation indicators [14]. For these and other reasons, implementing a mix of gray and green infrastructures is often the best solution, benefiting from the advantages of both measures to enhance the sustainability and resilience of risk management strategies [11, 22].

To include protective forests in IRM strategies throughout the Alpine Space, science, practice, and policy need to address the above-mentioned deficits and knowledge gaps. However, the foundation for a clear communication among scientists, practitioners, policy makers, and with the public as well as a common understanding of existing protective forest management guidelines need to be established first.

2. Defining protective forests as Eco-DRR measure

“A protection [or protective] forest is a forest that has as its primary function the protection of people or assets against the impacts of natural hazards or adverse climate” [24].

That is, in the context of natural hazard risk, 1) a hazard that may cause damage, 2) people or assets that may be damaged, and 3) a forest that has the potential to prevent or mitigate this damage must be present, so that this forest can have a protective function [41]. In addition to the general need for the protection of people and assets by forest, the protective function is also associated with the protective potential of a location (either currently covered by forest vegetation or not), which is the “protective effect that a forest is likely to have if properly managed” [27]. That is, the “protective effect” refers to the degree of hazard mitigation by forest, which depends on the current canopy cover and stand structure (see also chapter [42] of this book).

However, the terms “protective function” and “protective effect” are often used inconsistently, synonymously, and sometimes misleadingly throughout the Alpine Space, which originates from country-specific forest legislations [43, 44, 45]. To support a common understanding, Kleemayr et al. proposed a consistent protective forest definition matrix (originally “Protection forest definition matrix”; [46]) with the aim to disentangle and illustrate the similarities and differences between existing terms (Figure 3) [47].

Figure 3.

Adapted reprint of the main figure from the “Protection forest definition matrix” [46]—An illustration of similarities and differences between sometimes contrarily defined and used terms regarding protective forests in the Alpine Space. Column 1: orange = soil protective forest (F1 = protective function, E1 = protective effect); column 2: red = protective forest growing in natural hazard starting, transit and runout zones; column 3: dark red = direct object protective forest; column 4: blue = indirect object protective forest; green = current forest or potential forest (land) use area; E1–E4 show forest areas that have a protective effect (tree elements) and forest gaps without a protective effect (full color). For details, see [46, 47].

The term protective function is mainly applied in land use and strategic forest management planning, such as the forest development plan in Austria (“Waldentwicklungsplan” WEP; [48]) or the forest function maps in Germany (“Waldfunktionskarten” based on § 1 and 12 BWaldG [49]). That is, to control land use development, plan silvicultural interventions and regulate harvesting, desired forest functions such as protection, recreation, timber production, or climate and water regulation (i.e., forest ecosystem services) are spatially defined and mapped. The concept of forest functions therefore translates social and economic interests into land use regulations and forest management practices and is commonly applied, for example, in Italy where “Forests having the function of direct protection of inhabitants, of strategic assets and infrastructures, identified and recognized by Regions and Autonomous Provinces, cannot be transformed and the land use cannot be changed […]” (Legislative Decree 34/2018 “Consolidated Law on forests and forestry chains,” Article 8, Subparagraph 7; [43]). This understanding of the protective function is, for example, translated into the definition by the Konferenz der Kantonsoberförster (KOK 2007; conference of the Swiss cantonal head foresters): a protective forest is a forest that can protect an acknowledged damage potential against a recognized natural hazard or reduce the associated risks [50, 51]. This definition is one of the most particular ones of de facto legality specifically including the terms natural hazard and risks. In contrast, in French or Slovenian forest legislations, protective forests can also be “[…] forests located on the periphery of large urban areas” (French Forest Code, Code forestier; [43]), or “Forests in adverse ecological conditions which protect themselves, their land and lower-lying land […].” (Slovenian Forest Act; ZG, Article 43 [52]), or have additional tasks such as to protect the soil from degradation and erosion, and to ensure forest growth capacity as stated in the Austrian Forest Act (ForstG [53]).

The protective forest definition matrix by Kleemayr et al. [46] combines elements from existing national legislations; however, it does not include all environmental conditions and criteria that define protective forests in national forest laws of the Alpine Space. The matrix defines “A forest with a protective function designation [as] a forest or potential forest area intended to protect against soil degradation and/or natural hazards” and uses the term “protective effect” in the context of disaster risk reduction. That is, “the protective effect describes the actual protective capacity of a forest against natural hazards and/or soil degradation” in dependence of its structure, which is a regulating ecosystem service according to the Millennium Ecosystem Assessment framework [54]. Applying the term protective effect therefore implies an evaluation of the forest structure, which allows one to assess the actual degree of provided protection against natural hazards. For example, a high protective effect against rockfall is only possible, if a forest has a certain number of stems, basal area, stem diameter distribution, or tree species composition in rockfall transit and/or deposit zones to stop falling rocks (see chapter [42] of this book); however, even if the protective effect of a forest stand is low or the vegetation cover is temporarily absent, it could still have an important protective function due to its uphill location above assets.

The national definitions that are combined in the protective forest definition matrix imply that not only a hazard (potential), but also a natural hazard risk, i.e., a damage potential (the assets to be protected by forest and their entities, which are called “objects” in the context of protective function mapping; see chapter [55] of this book), must be present when declaring a forest area as an object protective forest. Object protective forests are forests, which are located in process areas of natural hazards that endanger objects below and can have 1) a direct protective function and, if applicable, protective effect against gravitational natural hazards such as rockfall, shallow landslides, or snow avalanches, allowing to directly link the precise locations of the hazard and the endangered objects; or 2) an indirect object protective function (and effect) for floods and other water-related natural hazards [51]. The latter relationship is defined as indirect since an entire forested catchment can contribute to flood protection (see chapter [56] of this book), and it is not straightforward to establish a direct connection between a precisely located forest area and a flooding scenario, especially when applying protective forest models (see chapter [57] of this book).

The matrix of definitions and classifications proposed by Kleemayr et al. [46] can support incorporating protective forests as Eco-DRR solution into IRM concepts, distinguishing direct and indirect object and site protective forests for prioritizing management activities that maintain and/or enhance their protective effects—actions that would promote the recognition of these forests as Eco-DRR measure and facilitate their utilization in IRM strategies. Nonetheless, the shift toward an IRM that includes FbS into the portfolio of available measures is still incomplete, also due to difficulties in translating research results into policy and further into useful and harmonized information for practitioners (see also chapter [58] of this book).

3. Regulations and guidelines for managing protective forests in the Alpine Space

3.1 Forest policy needs to utilize Forest-based Solutions for Eco-DRR

The mid-nineteenth century marked an important turning point for raising concerns about large-scale deforestation impacts on soil erosion and flood events in several Alpine countries. The following debate began, for example, in France and Austria, realizing that it was necessary to reestablish the protective functions and effects of mountain forests that have been impaired by centuries of overgrazing and overexploitation [59, 60]. France introduced the first nation-wide legal regulation on protective forests in 1803, which was perpetuated in 1827 with the Code forestier; however, the regulations were not comprehensive and were limited to a ban on deforestation of mountain slopes. The absence of specific legislations for mountain areas was strongly felt by politicians and forest managers as, for example, proven by the declaration of Ludovic Beaussire, special editor and contributor to the first volume of the Annales forestières (Forest Annals) of 1842: “The considerations, which make the reforestation of the mountains a necessity, impose on the government, as one of its most pressing and sacred duties, the obligation to provide for it [61].” In Austria, it was catastrophic flood events (e.g., 1847 in Salzburg) that increased the awareness for the need of a sufficient forest cover to mitigate the devastating effects of natural hazards. This led to the implementation of the first Austrian Forest Act in 1852 (“Reichsforstgesetz”), which was replaced in 1975 [53], ensuring the conservation of forests and their soils to best provide the forest effects, namely timber production; protection against natural hazards and other damaging environmental impacts including soil erosion; regulation of climate, water, and air; and recreation (ForstG 1975 idF 2002, § 1 (2), § 6 (2) [53]). Few years after the implementation of Forest Acts with special regulations on protective forests in Austria and Bavaria in 1852, the French government of the Second Empire implemented a definition of forests to be protected from deforestation because of their protective effect in 1859 in the Code forestier and established the first law mandating Alpine reforestation in 1860. However, this law was negatively perceived by mountain peasants since it threatened their pasturing, a necessity for their livelihood [62]. This law has therefore been modified in 1882 to the law on restoration and conservation of Alpine lands and the word reforestation was omitted from the title, shifting the focus of forest management activities from extending forest areas to “restore mountain land by correcting torrents, regulating pastures and planting eroded watersheds” [63]. This law is the basis of French legislation dedicated to the sustainable management of the ecosystem service “protection against natural hazards” and was the model for legislations of many Alpine Space countries such as the Austrian Act of 1884 on torrent control, laying the foundation of Alpine land restoration. However, it was the 1922 Chauveau law that established the legal status of “protective forestry,” acknowledging the major role of forests in natural hazard prevention and risk mitigation for lowland areas, which were becoming more and heavily industrialized [59]. The acknowledgment of the protective effects of forests is one factor, but its implementation in forest management practices is often impeded by the lack of a comprehensive mapping of forests with a protective function (see also chapter [55] of this book). Eventually, any legislation can be improved, considering the increase in knowledge and changes in the paradigms of the implementation of measures.

One objective of the Interreg Alpine Space project GreenRisk4ALPs [64] was to propose ways to improve current forestry policies in the Alpine Space. Hence, a SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis was conducted by experts for (protective) forest legislations in Austria, France, Bavaria (Germany), Italy, and Slovenia [65]. A summary, based on this SWOT analysis, of the general existence of regulations, tools, and standardized methods to support the management of protective forests as an FbS for Eco-DRR is given in Table 1.

	Administrative level	Austria		France		Germany		Italy		Slovenia
Existence of:		YES	NO	YES	NO	YES	NO	YES	NO	YES	NO
Regulations for risk prevention	national	X			X	X			X	X
	regional	X		X			X	X		X
Protective forest definition and/or classification	national	X		X		X			X	X
	regional		X	X			X	X		X	X
Comprehensive mapping of natural hazards	national	X			X	X		X			X
	regional	X		X		X		X			X
	local	X		X		X		X			X
Comprehensive mapping of natural hazard risks	national		X		X		X	X			X
	regional		X		X	X		X			X
	local		X		X	X		X			X
Comprehensive mapping of the ecosystem service “protection”	national	X		X		X			X	X
	regional	X		X		X			X	X
	local	X		X		X			X	X
Funding for the provision of the ecosystem service “protection”	EU	X			X	X		X		X
	national	X			X	X			X	X
	regional	X			X	X			X		X
	local	X		X			X		X		X
Natural hazard risk prevention documents that integrate the ecosystem service “protection”	national	X			X		X		X	X
	regional	X			X		X		X	X
	local	X			X		X		X	X
Standardized methodology for risk zoning	national	X		X		X			X	X
	regional	X		X			X	X		X
	local	X		X		X		X		X
Protective forest management guidelines	national	X		X		X			X	X
	regional	X		X		X		X		X
	local	X		X		X			X	X
Societal demand for valuing Forest-based Solutions		X		X		X		X		X

Table 1.

Summary of the general existence of regulations, tools, and standardized methods in selected Alpine Space countries, supporting the management of protective forests as FbS for Eco-DRR. Adapted from [65].

Based on this SWOT:

• Clearly defining protective forests and their functions in forest legislations,

• Specifying methods, data, and tools to be applied for protective forest mapping,

• Defining and legitimizing operational protection targets and priorities for assets related to risk,

• Increasing the quality of geodata necessary to assess protective functions effectively,

• Spatially covering all relevant hazard and damage potentials in hazard and risk zoning,

• Implementing common standards to assess protective effects and the stability of protective forests,

• Collecting high-quality data on past natural hazard events and pre-event forest condition in a harmonized way to improve protective effect assessments,

• Developing and implementing an efficient participatory approach for land use and forest planning,

• Bundling competences in hazard and forest ecosystem services’ assessments to improve their results and acceptance,

• Connecting key stakeholders in the field of natural hazard risk management and, whereby, harmonizing their interests with societal demands,

• Addressing the current lack of adapted financial funds and of clear rules to allocate these funds dedicated to protective forest managements,

• Legally combining hunting and forestry regulations,

• Increasing public awareness for protective forests and their key function, and

• Developing clear communication and dissemination strategies about the efficiency and limits of FbS,

are only a few recommendations to enhance current (protective) forest policies and legislations to support improving the relevance of FbS in IRM (for further information and details see [65]).

3.2 Risk in current European protective forest management guidelines

It was early recognized by those responsible for natural hazard and forest management in the Alpine Space that reducing the risk from natural hazards endangering people and damaging assets requires the expansion of forest areas [66], especially at high altitudes and in torrent catchments [67], as well as special silvicultural treatments of forests with a protective function. However, first regional regulations and measures were limited to restrict or ban deforestation, grazing by farm animals, and timber removal in forests on steep mountain slopes. These regulations were formulated in the medieval concept of protected forests (so-called Bannwälder), which are still a legal category of direct object protective forests in Austria and Bavaria. Deforestation and forest thinning, which increased with population growth, required actions to protect against natural hazards but also to secure local timber supply in a phase of increasing economical protectionism. Following devastating flood disasters and increasing demand for timber in the nineteenth century, national forest laws with special regulations for protective forests and torrent control were introduced and extensive reforestation programs were launched (see Section 3.1).

Even if regulations and silvicultural measures in the nineteenth and early twentieth century focused on (protective) forest conservation, reforestation, and afforestation, it was known that the protective effects of forests depend on their structure and thus on their management. However, despite emphasizing the importance of protective forest management in the literature, clear concepts for determining the object protective functions and protective effects based on site-specific hazard susceptibilities, damage potentials, and forest conditions were still missing until the end of the twentieth century.

After the Second World War and until the end of the 1980s, structural river regulation, and technical torrent and avalanche control boomed in the European Alps. These measures were further developed and implemented at great expense. Meanwhile, hardly any approaches were developed to quantify the protective effects of forests against gravitational natural hazards. In this period, only a few studies mainly from Japan (e.g., [68, 69]) and Switzerland (e.g., [70, 71]) addressed the influence of forest structure on snowpack stabilization based on systematic observations or snow mechanical considerations. However, the results of these early and valuable studies are difficult to integrate into avalanche risk analysis since they lack important factors as well as the large variation in forest conditions influencing the protective effects. In addition, they did not offer methods for calculating the impact of forest on onset and propagation probabilities that are required to determine the risk (see section 1).

The first experimental study on the influence of forest on the runout of rockfall did not appear until 1988 [72]. While studies on the protective effects of forests against landslides were carried out early in Japan (e.g., [73]) and in North America (e.g., [74, 75, 76]), this topic was reduced to bioengineering measures and taken up rather late in Europe. Moreover, studies about landslide-forest interactions mainly focused on the differences between forest and other land cover types and the effects of clear cutting, that is, the presence or absence of forest cover was treated as a general parameter. Although approaches to predict slope stability considering the canopy coverage of woody vegetation appeared in the 1970s (see [77]), the influence of its structural characteristics on the probability of landslide occurrence has been rarely investigated.

Mountain forest research in Europe mainly addressed silvicultural topics such as forest type identification, natural regeneration, reforestation, high-altitude afforestation, and stand tending for stability. The first comprehensive books published by Mayer (1976) in Austria [78] and Bischoff (1984) in Switzerland [79] giving practical advice for the management of Alpine mountain forests provided some checklists for assessing the protective functions and effects of forests but were still little oriented toward natural hazard risk assessment [80]. Perhaps the economic and technical possibilities for implementing gray infrastructures and their great success have contributed to the fact that forest research was limited to silvicultural questions and that hardly any research funding has been made available to study the protective effects of forest. However, by the end of the 1970s, the limited effects and capacities for disaster risk reduction by gray infrastructures only were increasingly recognized, especially in flood and torrent control, which can be observed in many regions worldwide and is called the paradigm shift in flood risk management (see also chapter [56] of this book). Disaster prevention and mitigation strategies were supplemented through spatial planning (hazard zoning), which indirectly led to an increasing need to assess the protective functions and effects of forest. Furthermore, the consequences of forest dieback in Europe caused by air pollution in the 1980s and the adverse impacts of climate change became increasingly apparent in mountain areas in the 1990s. Considerable forest damages by storm and bark beetle outbreaks in the 2000s as well as questions of funding policies in hazard mitigation and forestry pushed new studies about protective effects of forests (e.g., [81, 82]), protective forest management planning, and a second generation of silvicultural guidelines including procedures for hazard-related forest assessment and management [80].

In the frame of the Interreg Alpine Space project GreenRisk4ALPs [64], Perzl and Kleemayr [80] analyzed the general concepts of five of these current European protective forest management guidelines—the Swiss guideline NaiS [83], the Italian SFP [84], the French GSM-N [85] and GSM-S [86], and the Austrian guideline ISDW [87]—in terms of applicability for hazard risk management. Furthermore, they evaluated the hazard-related criteria and thresholds proposed by the guidelines, which are protective effect-related indicators for hazard risk assessment and targets for forest management (see chapter [42] of this book).

All these guidelines follow the structure and the criteria of the Swiss guideline NaiS but differ in many crucial details considerably. According to Perzl and Kleemayr [80], they incorporated new scientific knowledge and structured the support of planning and decisions into 1) the assessment of the natural hazard risk (as hazard and damage potentials in terms of basic hazard susceptibilities or protective functions of forest, and in terms of forest conditions, which provide protective effects), 2) the assessment of stand stability and regeneration, and 3) general recommendations on silvicultural treatments. This concept of first classifying the protective functions of forests based on indicators for the hazard potential and the exposure and vulnerability of assets (damage potential) and then classifying the protective effects based on silvicultural targets is a simplified risk-based approach suitable for protective forest management.

However, this concept is implemented to varying degrees of completeness in the guidelines. Some of these guidelines do not fully support forest function mapping and, therefore, risk evaluation since they do not consider the damage potential. All guidelines provide little support for delineating spatial evaluation units, which remains an unsolved issue of spatial scales and fragmentation of management units situated between traditional forest stand mapping and appropriately resolved units for protective effect and hazard analyses. Furthermore, the results of the proposed methods for assessing the protective functions and effects of forests are still of limited value for risk analyses, as they only refer to hazard initiation, partly based on fuzzy indicators of hazard susceptibility, or, if considering hazard propagation as in the case of rockfall, they mainly neglect the cumulative effects of terrain and forest on the slope scale. Some of the guidelines even do not provide clear instructions for how to combine the proposed indicators and thresholds (targets) to quantify cumulative protective effects. Although they specify single objectives for forest conditions to be reached with silvicultural measures and indicators of how to monitor their success, which are the main aims of the guidelines, they are thereby ambiguous about the protective effect in terms of hazard probability and magnitude and thus about the natural hazard risk.

The validation of the protective effect-related forest characteristics proposed by the guidelines based on observed natural hazard events in forests shows the main limitation for their application in natural hazard risk management: the procedures, indicators, and thresholds to assess the protective effects of forest against gravitational natural hazards lead to either a considerable or an extremely low misclassification rate, the latter resulting primarily from high forest density targets (for further details, see chapter [42] of this book). This may result in over- or underestimating the protective effects of forests and thus in incorrect assessments of the risk from natural hazards endangering people and damaging assets.

Although research on protective effects of forests has increased since the late 1980s (e.g., [19, 88, 89]), but especially on rockfall-forest interaction in Switzerland and France [90], the current European protective forest management guidelines are still based on few data-driven studies without international survey and quality standards [80]. Therefore, they are difficult to interpret and to implement into risk-based protective forest management approaches. Moreover, uncertainties in assessing protective effects of forest are still considerable (e.g., [91]; see also chapter [40] of this book.), which could be the main reason affecting confidence in FbS in contrast to gray infrastructure.

4. Conclusions

Impacts of climate change on societal and environmental systems are serious threats to the development of mountain areas worldwide. Mountain forests can protect people and assets against natural hazards making the Alpine Region inhabitable. Protective forests are Forest-based Solutions (FbS) as a specific case of Nature-based Solutions (NbS) and are often implemented as Ecosystem-based Disaster Risk Reduction (Eco-DRR) measure together with spatial planning activities and gray infrastructure within an integrated risk management (IRM). However, few economic evaluation methods are currently available to compare the cost-effectiveness of protective forests and technical measures, despite implementing a mix of gray and green infrastructures is often the best solution, benefiting from the advantages of both to enhance the sustainability and resilience of risk management strategies.

To facilitate the utilization of protective forests in IRM strategies throughout the Alpine Space, science, practice, and policy need to address the deficits and knowledge gaps that we identified in this chapter. They include 1) a common understanding and definition of protective forests, 2) existing national barriers for implementing Eco-DRR in the Alpine Space, and 3) the applicability of protective forest management guidelines in risk-based forest management approaches for prioritizing management activities that maintain and/or enhance the protective effects. Despite the societal demand for valuing FbS, the ecosystem service “protection against natural hazards” provided by mountain forests is currently often not considered in local, regional, national, and/or European policies and regulations.

Improving current (protective) forest legislations by financing and considering practice projects and research addressing protective functions and effects of mountain forests and changes in the paradigms of the implementation of protection measures can enhance the relevance of FbS in IRM. Moreover, although research on protective effects of forests has increased in recent decades, current European protective forest management guidelines are still based on few studies and are difficult to implement into risk-based protective forest management approaches. Establishing international survey and quality standards for assessing protective effects and, therefore, reducing the associated uncertainties could also significantly increase the trust in FbS compared with gray infrastructure.

Ultimately, the shift toward an IRM that includes FbS into the portfolio of available risk mitigation measures requires translating research results into useful and harmonized information for practitioners (see also chapter [58] of this book).

Acknowledgments

This work was conducted in the context of the GreenRisk4ALPs project (ASP635), which has been financed by Interreg Alpine Space program, one of the 15 transnational cooperation programs covering the whole of the European Union (EU) in the framework of European Regional policy.

Conflict of interest

The authors declare no conflict of interest.