Introduction
Coastal dune systems are formed by the interaction of marine, aeolian and terrestrial processes and are widely recognised as priority habitats in international conservation frameworks due to their ecological, geomorphological and socio-economic importance (Goldsmith 1985, Martínez et al. 2008, Martínez et al. 2013, Psuty and Silveira 2010, Hesp 2011, Hesp 2024, Hesp and Walker 2013, Nordstrom 2015, Luijendijk et al. 2018, Chadwick et al. 2022, Prodanov et al. 2023, Rangel-Buitrago et al. 2023, De Freitas 2024). Often described as part of the Coastal Transition Zone (CTZ), dune systems function as natural buffers that mitigate marine forcing, reduce shoreline erosion and preserve the integrity of the land–sea interface (Maun 2009). Beyond their protective role, dunes contribute to groundwater retention and purification, the regulation of local microclimates and the maintenance of habitats for highly specialised flora and fauna adapted to sandy, saline and wind-exposed environments (Pérez-Maqueo et al. 2013). As such, they deliver a broad range of ecosystem services, including storm and erosion protection, sediment storage for beach nourishment, carbon sequestration in dune vegetation and the provision of habitats for rare, endemic and threatened species (Carter et al. 1991, Feagin et al. 2005, Doody 2013). In addition, coastal dunes support recreational and tourism activities and hold cultural and educational value for coastal communities (Nordstrom 2000, Pérez-Maqueo et al. 2013, McLachlan et al. 2013). As integral components of sandy beach–dune systems, coastal dunes also function as dynamic land–sea interface units that ensure sediment continuity, ecological connectivity and natural buffering against marine forcing (McLachlan and Brown 2006).
Coastal zones concentrate a wide range of natural, cultural and economic assets within a limited spatial extent, making them amongst the most intensively used and contested environments worldwide. Residential and recreational settlements, infrastructure, economic activities, specialised tourism (e.g. dunes as geomorphosites for geotourism), archaeological heritage and biodiversity-rich ecosystems are frequently juxtaposed within the same coastal space. Within this complex mosaic, beach-dune systems occupy a particularly sensitive position, as they must simultaneously sustain ecological functions, provide socio-economic services and absorb multiple forms of human pressure, especially in the context of sun-and-sea tourism (Martínez et al. 2013, Marrero-Rodríguez and Dóniz-Páez 2022, Johnston et al. 2023).
Situated at the land–sea interface, coastal dune landforms are amongst the most dynamic geomorphic features, continuously reshaped by waves, storms and sea-level fluctuations, while also being strongly modified by human activities (Huggett 2011, Milne et al. 2012, Foti et al. 2021, D’Alessandro et al. 2022, Fontán-Bouzas et al. 2022, Prodanov et al. 2023, Rangel-Buitrago et al. 2023, Woodroffe et al. 2023, Prodanov et al. 2025). Their formation and evolution depend on three fundamental factors, sediment availability, wind regime and vegetation cover, resulting in high spatial and temporal variability shaped by the interplay of physical, chemical and biological processes (Pye 1983, Feagin et al. 2005, Aagaard et al. 2007, Psuty and Silveira 2010, Anthony 2013, Masselink et al. 2014, Nordstrom 2015, Delgado-Fernandez et al. 2019, Feagin et al. 2019, Costas et al. 2020).
Despite their ecological, protective and socio-economic importance, coastal dunes are amongst the most threatened ecosystems worldwide (Defeo et al. 2009). Their conservation status reflects a delicate balance between natural drivers, such as sediment budgets, beach morphodynamics and vegetation succession and multiple anthropogenic pressures. Major human-induced threats include resource exploitation, urbanisation, coastal infrastructure development, unregulated tourism, trampling, off-road vehicle use, mechanical beach cleaning, invasive species and littering (Heslenfeld et al. 2008, Carboni et al. 2009, Hesp 2011, Hesp and Walker 2013, McLachlan et al. 2013, Ciccarelli 2014, Valcheva et al. 2018, Valcheva et al. 2021, Mo et al. 2021, Ciccarelli et al. 2023, Hesp 2024). These pressures are increasingly compounded by climate-related hazards, including accelerated sea-level rise, increased storm intensity and altered sediment supply, which drive erosion, dune mobility, habitat loss and reduced system resilience (Sabatier et al. 2009, Ranasinghe 2016, Harley et al. 2017, Gao et al. 2020). As a result, degradation of dune systems compromises their capacity to deliver ecosystem services, with direct implications for both ecological integrity and human well-being (Hanley et al. 2014, Alessandrini et al. 2024).
The complexity and vulnerability of dune systems, coupled with their importance for ecosystem services, have spurred the development of targeted management and conservation strategies worldwide. Effective dune management requires integrated approaches that account for marine, aeolian and geological dynamics, while recognising the central role of vegetation in dune formation and stabilisation (Maun 2009). The overarching challenge lies in balancing habitat preservation with sustainable use by integrating ecological and physical processes with socio-economic and cultural considerations (Anfuso et al. 2014, Niavis and Tsiotas 2019, Mooser et al. 2022, Er-Ramy et al. 2022, Rangel-Buitrago and Gracia 2024). In this context, spatial mapping and classification emerge as fundamental management tools, forming the basis for coastal risk assessment and prioritisation of interventions. Coastal risk, commonly defined as the interaction between hazard probability and potential consequences, depends on the interplay between hazards and system vulnerability (Hieronymus and Kalén 2020). Existing coastal risk and vulnerability indices often prioritise physical and geological parameters, while incorporating socio-economic, ecological and cultural aspects to a more limited extent (Nguyen et al. 2016, Rocha et al. 2023). Management responses range from passive measures such as land-use zoning and legal protection to active interventions including dune stabilisation, habitat restoration and invasive species control (Martínez et al. 2013, Nordstrom 2015). However, these measures require robust, standardised assessment frameworks capable of integrating physical, ecological and socio-economic information to support evidence-based decision-making (Gallego-Fernández et al. 2011, Arens et al. 2013, Furlan et al. 2021). However, human interventions frequently constrain natural dune dynamics by altering sediment pathways, vegetation succession and morphological feedbacks, underscoring the need for assessment frameworks that explicitly account for anthropogenic pressure and management intensity (Nordstrom et al. 2015).
Recent coastal assessment frameworks increasingly emphasise the integration of geomorphological integrity, environmental quality, anthropogenic disturbance, and ecosystem functionality within unified management-oriented approaches (Lithgow et al. 2015, Pinna et al. 2022, Della Bella et al. 2024, Rangel-Buitrago et al. 2026). Numerous indices and assessment tools have been developed to evaluate dune condition, vulnerability and conservation status, reflecting different disciplinary perspectives and management objectives. These approaches can be broadly grouped into four categories. Ecological and vegetation-based indices focus on floristic diversity, vegetation structure and habitat quality as indicators of dune condition, including the H′dune index (Grunewald and Schubert 2007), the Mediterranean conservation status framework proposed by Carboni et al. (2009) and the vegetation-based risk index developed by Alessandrini et al. (2024). Geomorphological and physical condition indices emphasise dune morphology, sediment dynamics and exposure to erosive forces, including restoration-orientated approaches such as those discussed by Lithgow et al. (2015) and regional vulnerability frameworks (Peña-Alonso et al. 2018), as well as vegetation-based conservation indices applied by Pinna et al. (2015). Integrated eco-geomorphological indices combine physical and biological parameters to capture system complexity, notably the Coastal Dune Vulnerability Index (CDVI) and its subsequent refinements (Ciccarelli et al. 2017, Bertoni et al. 2019), as well as endemicity-focused extensions (Pinna et al. 2019). Finally, multidimensional socio-ecological and legal frameworks incorporate a broad set of drivers, including climate forcing, human use and legal protection, as exemplified by the Multidimensional Coastal Vulnerability Index (Furlan et al. 2021) and by checklist-based approaches (Bodéré et al. 1991, Bodéré et al. 1994), alongside restoration-focused tools such as the Dune Restoration Potential index (Pinna et al. 2022).
Despite their diversity, existing frameworks share several common limitations. Many are strongly context-dependent, hindering transferability without extensive local recalibration (Pye and Blott 2008, Gallego-Fernández et al. 2011). Others tend to over-emphasise either physical or ecological dimensions while under-representing complementary aspects. In particular, legal protection status, scientific research value and nuanced forms of anthropogenic pressure are rarely quantified in a systematic manner, limiting the usefulness of many indices for policy-orientated conservation planning (Furlan et al. 2021, Alessandrini et al. 2024). Differences in indicator selection, weighting schemes and scoring approaches further reduce comparability and repeatability across studies.
Addressing these gaps, the present study introduces the EGDVI. This unified, standardised and transferable framework integrates geomorphology, ecology, human pressures, legal protection and scientific value into a single operational assessment tool. The EGDVI is specifically adapted to the microtidal, fetch-limited conditions of the Black Sea coast, where dune dynamics, management practices and conservation challenges differ markedly from those of macro- and mesotidal environments.
Aim of the study
This study aims to develop and apply the EGDVI, a multi-criteria evaluation framework designed to overcome the limitations of existing dune assessment methodologies. The EGDVI comprises 31 indicators grouped into eight categories: Geomorphology (GM), Aeolian Dynamics (AD), Ecology (ECO), Pressure (PRS), Human Footprint (HFP), Legal Protection (LEG), Scientific Value (SCI) and Nature Conservation (CON). All indicators are scored on a standardised 0–4 scale, where higher scores indicate higher natural value or better conservation condition and are weighted, based on expert assessment and scientific review.
The framework is applied to the Strandzha dune systems along the southern Bulgarian Black Sea Coast, a region characterised by diverse coastal morphologies ranging from narrow pocket beaches backed by cliffs to broad, low-lying barrier systems. Although the Black Sea is microtidal, it exhibits complex sediment dynamics and distinct erosion behaviour associated with wind-driven waves and storm surges (Tătui et al. 2019). At the same time, most beaches are concession-managed and subject to regular levelling and mechanical cleaning, which obscures their natural state. For this reason, dune systems were selected as the primary units of assessment. This context enables the inclusion of Black Sea–specific indicators, enhancing the regional relevance of the EGDVI, while demonstrating its potential transferability to other low-energy coastal environments.
Results
Application of the Eco-Geomorphological Dune Value Index (EGDVI) to the 16 dune systems along the Strandzha coast reveals a pronounced differentiation in eco-geomorphological condition across the region. Total scores range from 154.0 to 364.5, out of a theoretical maximum of 400, indicating the co-existence of both highly preserved and severely degraded dune systems within a relatively compact coastal sector.
Based on the fixed classification thresholds (Fig. 4; Tables 3, 4), the assessed dune systems are unevenly distributed across value classes. Very high eco-geomorphological value (Class A) characterises four systems (25.0%), while high value (Class B) is represented by a single system (6.25%). The majority of dune systems (eight sites, 50.0%) fall within Class C – Moderate Value, reflecting intermediate condition. Low-value (Class D) and degraded systems (Class E) together account for three sites (18.75%), underscoring the presence of localised, but significant degradation hotspots along the coast.
Summary statistics (Table 4) indicate a strongly asymmetric distribution of EGDVI scores. Although a limited number of dune systems attain very high values, the regional mean score (266.1) and median (261.2) both fall within the moderate-value range. This highlights the dominance of transitional systems at the scale of the Strandzha coast, rather than a landscape uniformly characterised by either high conservation status or widespread degradation.
Class A – Very High Eco-Geomorphological Value
The highest eco-geomorphological values are recorded for Primorsko (Stomopolu–Perla), Primorsko (International Youth Centre), Koral and Camping Yug and Lipite (Fig. 4). These four systems form a distinct upper cluster, with EGDVI scores consistently exceeding 320 and a high mean value (347.4). Their relatively narrow interquartile range (IQR = 19.4) indicates limited internal variability and suggests that all four systems approach near-reference conditions.
From a geomorphological perspective, these dune systems are characterised by wide, continuous dune belts that often exceed 100–150 m and by well-developed morphological sequences, including incipient dunes, foredunes, secondary ridges and, locally, parabolic or cliff-top dune forms. Ecologically, they exhibit high vegetation integrity with clear zonation patterns, while anthropogenic pressure remains comparatively low. Favourable legal protection status and feasible conservation management further contribute to their consistently high scores.
Class B – High Eco-Geomorphological Value
Atliman represents the sole dune system classified as Class B – High Value. With an EGDVI score of 283.5, the system occupies a transitional position immediately below the Class A threshold. This indicates a high degree of geomorphological and ecological integrity, albeit constrained by localised pressures, such as regulated access and seasonal recreational use.
Although statistical dispersion measures are not applicable to a single system, Atliman’s proximity to the upper-class boundary suggests that relatively minor changes in management effectiveness could result in upward or downward reclassification. As such, the system exemplifies the sensitivity of high-value dune environments to subtle shifts in anthropogenic pressure.
Class C – Moderate Eco-Geomorphological Value
Class C – Moderate Value encompasses the largest and most regionally representative group, including Veleka River Mouth, Kiten, Butamyata, Ahtopol, Listi, Silistar, Nestinarka and Oazis (Fig. 4). With a mean score of 258.9 and a median of 259.2, these systems collectively define the prevailing eco-geomorphological condition along the Strandzha coast.
Despite their numerical dominance, Class C systems display relatively limited internal dispersion (IQR = 7.6), indicating broadly comparable levels of condition. Most retain functional dune units and key geomorphological elements, yet exhibit varying degrees of fragmentation, reduced sediment connectivity and visible anthropogenic influence, particularly within the foredune zone. The presence of several systems close to the upper threshold of this class, such as the Veleka River Mouth, highlights the potential for targeted management interventions to yield substantial improvements.
Class D – Low Eco-Geomorphological Value
Lozenets is classified as Class D – Low Value, reflecting a markedly reduced eco-geomorphological condition relative to the regional average. The system is characterised by a narrow, discontinuous dune belt, disrupted vegetation cover and diminished morphodynamic function. Although not yet fully degraded, its low score indicates limited resilience and a reduced capacity for natural recovery under current pressure regimes.
Class E – Degraded Dune Systems
The lowest EGDVI scores are observed at Tsarevo (Popski plazh) and Arapya, both classified as Class E – Degraded. These systems exhibit consistently low values with minimal variability, reflecting a uniformly advanced state of degradation. Extensive loss of frontal dune ridges, sparse psammophytic vegetation and a near absence of coastal-protection function characterise both sites.
Long-standing anthropogenic pressure, compounded by shoreline modification and storm impacts, has resulted in persistent degradation that is unlikely to be reversed without substantial and sustained restoration measures.
Regional patterns and management implications
Comparison between class-level statistics and the overall distribution of EGDVI scores highlights pronounced spatial heterogeneity along the Strandzha coast (regional IQR = 44.5). While a small number of dune systems retain near-reference conditions, the prevalence of moderately valued systems underscores the importance of proactive management. These transitional systems represent both a risk if pressure continues unchecked and an opportunity, as relatively modest interventions could significantly enhance their eco-geomorphological value.
Overall, the results demonstrate that the Strandzha coast simultaneously hosts some of the most valuable and some of the most degraded dune systems in Bulgaria, confirming the EGDVI’s effectiveness in discriminating between levels of condition and in supporting conservation prioritisation and evidence-based coastal management.
Case Study: Primorsko (Stomopolu–Perla) Dune System
To better illustrate how the EGDVI performs in a real-world context, a representative dune system from the Strandzha coast, Primorsko (Stomopolu–Perla), is examined in detail. The site reaches a total score of 364.5, placing it in Class A (Very High Eco-Geomorphological Value), which corresponds to a near-pristine system with outstanding geomorphological structure, ecological integrity and conservation importance (Fig. 5).
All geomorphological indicators (GM-1 to GM-5) receive the maximum score (4), pointing to a well-developed and continuous dune system with clear zonation from embryonic dunes to foredunes and secondary ridges. The dunes are both high (> 5 m) and wide (> 100 m), which places them in the highest class definitions. Hydrogeomorphic connectivity is fully functional, allowing active sediment and water exchange with adjacent environments. At the same time, the lack of fragmentation confirms that the system functions as a continuous, structurally intact dune corridor.
Indicators related to aeolian dynamics (AD-1 to AD-4 = 3) suggest a system that is active, but stable. Blowouts are present, but limited in extent (< 10%) and sand movement is visible, but not excessive. Deflation areas are small and localised, while dune breaches are shallow and episodic, without forming permanent channels. Sand supply remains sufficient to sustain dune development. Overall, this points to a balanced system in which aeolian processes are ongoing, but not leading to destabilisation.
Ecological indicators (ECO-1 to ECO-5 = 4) confirm a very well-preserved vegetation structure. Vegetation cover exceeds 60%, with clear zonation and strong representation of both pioneer species (e.g. Ammophila, Elytrigia) and typical psammophytes. Habitat diversity is high, including several dune habitat types, some of them of conservation priority. At the same time, the high score for habitat vulnerability reflects the presence of sensitive ecosystems that require continued protection.
Pressure and risk indicators show more variable conditions. Marine exposure is high (PRS-1 = 1), indicating strong wave energy impact, minimal topographic protection and frequent storm overwash affecting the dune front. Despite this exposure, the system remains overall stable, suggesting a certain degree of resilience to marine forcing. In contrast, degradation risk (PRS-2 = 3) reflects moderate, but manageable pressures, such as localised trampling or minor erosion. Macro-litter pollution (PRS-3 = 3) is noticeable, but not dominant, while the presence of invasive alien species (PRS-4 = 2) indicates limited, but detectable ecological disturbance.
Human footprint indicators reveal a mixed pattern. Permanent infrastructure and access paths (HFP-1 and HFP-2 = 4) are minimal or well managed, resulting in low direct physical disturbance. However, the recreational use intensity (HFP-4 = 2) indicates moderate visitor pressure, including localised trampling, particularly during peak seasons. Beach cleaning practices (HFP-3 = 3) suggest periodic mechanical intervention, which may have localised ecological effects.
Legal and management indicators are generally favourable. Land ownership and access regulation (LEG-1 = 4) indicate a relatively well-controlled regime, while protected area status (LEG-2 = 3) reflects partial, but not fully effective conservation coverage. Cadastral recognition (LEG-3 = 4) and scenic value (LEG-4 = 4) confirm both formal recognition and high landscape quality. However, the absence of designation under EU or national restoration frameworks (LEG-5 = 0) stands out as a clear gap, indicating that the site is not yet integrated into strategic restoration planning.
Scientific and conservation indicators (SCI-1, SCI-2, CON-1, CON-2 = 4) highlight the high research value and strategic importance of the system. The site includes well-preserved and representative geomorphological features, supports biodiversity of scientific interest and is suitable for long-term monitoring and conservation initiatives. The high feasibility of restoration further suggests that management interventions, if needed, could be effectively implemented.
Overall, the Primorsko dune system can be considered a highly functional and largely intact coastal environment, where natural processes and ecological structure are well preserved. At the same time, the presence of moderate human pressures and gaps in policy integration highlights the need for targeted and proactive management. This case study demonstrates the ability of the EGDVI to capture both the high conservation value of dune systems and the more subtle pressures that may influence their long-term stability.
Discussion
Regional adaptation
Most existing dune assessment and valuation frameworks have been developed for macro- and mesotidal coastal environments, where tidal range exerts a dominant control on sediment exchange, dune morphology and disturbance regimes (Carter et al. 1991, Nordstrom 2000, Pye and Blott 2008). In such settings, frequent overwash, strong tidal currents and extensive intertidal zones fundamentally shape dune dynamics, often resulting in rapid morphological change and highly mobile vegetation patterns.
In contrast, the Black Sea coast represents a microtidal, fetch-limited basin, where aeolian transport, wind-generated waves and episodic storm surges dominate coastal dynamics, while tidal forcing is negligible (Lin-Ye et al. 2018, Saprykina and Kuznetsov 2018). Under these conditions, dune systems tend to persist over longer timescales, sediment–vegetation feedbacks are more stable and successional stages often reach greater maturity than in high-energy tidal environments. These characteristics substantially influence both the expression of disturbance and the pathways of degradation and recovery, making direct transfer of assessment frameworks developed for mesotidal coasts problematic.
The need for region-specific adaptation of dune assessment approaches has been explicitly recognised for other low-energy or semi-enclosed seas, including the Baltic and parts of the Mediterranean (Bagdanavičiūtė et al. 2015, Ciccarelli et al. 2017). The EGDVI directly addresses this need by integrating eco-geomorphological indicators tailored to the Black Sea context, together with dimensions reflecting anthropogenic pressure, legal protection, conservation feasibility and scientific value. These latter aspects are often treated implicitly or qualitatively in earlier indices (Doody 2013, Alessandrini et al. 2024). Their explicit quantification enables the index to capture not only the physical and ecological condition of dune systems, but also their institutional recognition and relevance for conservation planning.
An additional rationale for focusing explicitly on dune systems rather than the full beach–dune continuum arises from contemporary coastal management practices in Bulgaria. Large sections of the active beach are subject to mechanical grooming, levelling and cleaning associated with concession management. Such practices suppress natural geomorphological signals and significantly alter ecological patterns, particularly those related to early successional vegetation (Carboni et al. 2009, Malavasi et al. 2014). Under these conditions, dune systems constitute a more stable, interpretable and ecologically meaningful unit for conservation-orientated assessment than beaches.
This distinction is particularly important given that many existing indices explicitly assess the beach–dune system as a coupled unit, thereby integrating processes and pressures that are fundamentally altered by intensive beach management. By isolating dune habitats as the primary unit of analysis, the EGDVI avoids this methodological bias and ensures that assessed patterns reflect intrinsic eco-geomorphological processes rather than artefacts of beach maintenance.
Class-based interpretation of EGDVI results
The class structure derived from the EGDVI highlights that differences amongst dune systems along the Strandzha coast are not merely numerical, but reflect qualitatively distinct eco-geomorphological states. Rather than forming a continuous gradient, the systems cluster into value domains that correspond to recognisable combinations of physical integrity, ecological maturity and governance context. This pattern is consistent with the asymmetric score distribution and class-level statistics, which indicate both strong differentiation and pronounced regional heterogeneity.
The use of fixed class thresholds facilitates interpretation beyond relative ranking, enabling the identification of meaningful transitions between conservation states. As such, the EGDVI classes provide a structured framework for linking observed eco-geomorphological conditions with management priorities and feasible intervention pathways.
Patterns and internal differentiation within classes
Systems classified as Class A – Very High Eco-Geomorphological Value form a compact and coherent group. Their high mean scores and relatively limited internal dispersion indicate near-reference conditions across multiple dimensions. These systems consistently combine well-preserved geomorphological structure, advanced vegetation zonation, low anthropogenic pressure and favourable legal and management conditions. Importantly, no single indicator group dominates the final scores. Instead, very high values emerge from the cumulative alignment of geomorphological, ecological and governance-related factors.
At the same time, internal differentiation within Class A indicates that near-reference conditions can be achieved through different, yet equally stable, configurations. Some systems attain very high values primarily through exceptional geomorphological development, while others are reinforced by strong legal protection, long-standing scientific recognition or high feasibility of conservation management. This diversity suggests that the very high eco-geomorphological value is not tied to a single idealised system type, but can arise through multiple pathways.
The sole Class B – High Value system occupies a transitional position that is particularly informative from a management perspective. Its physical structure and ecological integrity closely resemble those of Class A systems, yet relatively modest pressures related to access and seasonal recreation constrain its overall performance. This distinction suggests that the boundary between high and very high value is often governed less by intrinsic physical limitations than by the effectiveness of governance and visitor management.
Class C – Moderate Value represents the most extensive and regionally dominant group. Although all systems within this class retain functional dune elements and active eco-geomorphological processes, they differ substantially in their dominant constraints. In some cases, sustained human pressure is the primary limiting factor, while in others, reduced width, fragmentation or altered sediment connectivity play a more important role. Several systems occupy threshold positions close to the Class B boundary, indicating sensitivity to relatively small changes in pressure or management effectiveness. Despite a relatively narrow dispersion of scores, Class C should, therefore, be interpreted as a transitional domain rather than a uniform condition, encompassing multiple degradation and recovery trajectories.
Class D – Low-Value systems exhibit reduced geomorphological functionality under persistent pressure, resulting in limited natural recovery potential. While not fully degraded, these systems lack the resilience required for spontaneous improvement and, therefore, require structured, intervention-orientated management.
Finally, Class E – Degraded systems display uniformly low scores and minimal internal variability, reflecting an advanced and relatively homogeneous state of degradation. Near-complete loss of frontal dune structure, disrupted sediment pathways and sparse psammophytic vegetation indicate that degradation has progressed beyond reversible thresholds under current conditions.
Linking EGDVI classes to management and restoration frameworks
The class structure produced by the EGDVI aligns closely with the logic underpinning contemporary management- and restoration-orientated dune frameworks. Unlike risk- or vulnerability-focused indices, which primarily prioritise sites based on exposure and sensitivity, the EGDVI reflects cumulative eco-geomorphological value and governance context, allowing management decisions to be guided not only by threat levels, but also by long-term conservation significance.
Class A systems correspond to conservation-priority contexts where strict protection and long-term monitoring should take precedence over active intervention, consistent with best-practice guidance for intact dune systems (Denning et al. 2024). These systems align with the “protection-only” category of the ReDune framework (Lithgow et al. 2015) and with low-urgency categories of the Dune Restoration Potential (DRP) index (Pinna et al. 2022).
Class B systems represent a preventative management tier in which relatively modest measures, such as access regulation, boardwalk installation and fencing, can prevent further degradation and facilitate upward transition. Evidence from comparable coastal settings indicates that such measures are effective in reducing trampling and informal path proliferation (Nordstrom 2015, Denning et al. 2024).
Class C systems align most closely with restoration-orientated categories, in which targeted interventions can substantially improve eco-geomorphological conditions. Measures such as access control, invasive species management, cadastral clarification and re-vegetation with dune-building species are widely recognised as effective for moderately degraded systems (Denning et al. 2024). The numerical dominance of this class along the Strandzha coast highlights both the vulnerability of the regional dune landscape and its potential for meaningful improvement through coordinated management action.
Class D and Class E systems correspond to progressively more demanding restoration and rehabilitation contexts. In these cases, recovery depends not only on ecological measures, but also on policy decisions, long-term institutional commitment and, in some instances, acceptance that full restoration may not be feasible (Lithgow et al. 2015, Pinna et al. 2022).
Comparative positioning of the EGDVI amongst dune assessment indices
Over recent decades, dune assessment indices have evolved from checklist-based vulnerability approaches towards more integrated eco-geomorphological and management-orientated frameworks, although the majority remain primarily focused on condition, vulnerability or risk rather than on integrated value assessment (Bodéré et al. 1991, García-Mora et al. 2001 etc.) - Table 5. Eco-geomorphological indices such as the Coastal Dune Vulnerability Index (CDVI) represented an important methodological advance by explicitly integrating physical, ecological and anthropogenic dimensions (Ciccarelli et al. 2017, Bertoni et al. 2019 etc.) - Table 5. However, these frameworks rarely incorporate legal recognition, governance effectiveness or scientific significance as explicit and independently weighted quantitative components.
The EGDVI advances the state of the art by explicitly integrating governance- and knowledge-related indicators alongside eco-geomorphological variables, thereby strengthening the science–policy interface (Doody 2013, Alessandrini et al. 2024). Unlike highly data-intensive multidimensional CVI or risk-based frameworks, which often require extensive ecological, socio-economic and spatial datasets and are best suited to large-scale applications (Furlan et al. 2021), the EGDVI is intentionally designed as a medium–high complexity, but standardised workflow, balancing analytical depth with operational applicability at the regional scale.
Although the conservation status of dune habitats in Bulgaria is formally assessed under the reporting framework of the EU Habitats Directive (Council Directive 92/43/EEC 1992), these assessments are often associated with considerable uncertainty due to broader challenges in Natura 2000 implementation, including limited standardised field-based monitoring and methodological inconsistencies (Tzonev et al. 2023). Consequently, national-scale evaluations may not fully reflect the spatial heterogeneity and site-specific ecological conditions of coastal dune systems.
In this context, the Eco-Geomorphological Dune Value Index (EGDVI) is not directly equivalent to the conservation status categories applied under Article 17 (Council Directive 92/43/EEC 1992) reporting, as it follows a different conceptual and methodological approach. Rather than focusing solely on habitat conservation status, the EGDVI provides an integrative site-scale assessment that combines geomorphological integrity, vegetation structure, anthropogenic pressures, legal and management characteristics, scientific significance and restoration potential within a unified framework.
As such, the EGDVI should be viewed as complementary to Article 17 assessments (Council Directive 92/43/EEC 1992), offering an additional evidence-based perspective that may help reduce uncertainty and support more spatially explicit and operational conservation evaluations in future reporting cycles.
By combining fixed classification thresholds with sensitivity analysis and by explicitly linking classes to management and restoration pathways, the EGDVI moves beyond descriptive assessment towards actionable conservation planning. In this sense, it synthesises the strengths of previous indices while introducing a governance-aware, value-based and class-orientated framework tailored to low-energy, microtidal coastal environments such as the Black Sea.
Conclusions
The Eco-Geomorphological Dune Value Index (EGDVI) provides an integrated, standardised and repeatable framework for assessing the conservation value of coastal dune systems by combining geomorphological structure, ecological condition, anthropogenic pressure, legal protection and scientific value within a single operational tool. Its application to 16 dune systems along the Strandzha sector of the Bulgarian Black Sea coast produced total scores ranging from 154.0 to 364.5 (out of a theoretical maximum of 400) and resulted in a clear five-class structure under fixed classification thresholds.
Beyond individual site classification, the results allow a synthetic regional interpretation of dune condition along the Strandzha coast. The mean EGDVI score for all assessed systems is 266.1, with a median of 261.2, placing the overall regional condition within the moderate-value class (Class C). This regional average does not represent a new index, but rather a descriptive benchmark that captures the dominant eco-geomorphological state of the coastline as a whole.
The regional mean highlights that, despite the presence of several near-reference dune systems with very high eco-geomorphological value, the Strandzha coast is predominantly characterised by transitional dune systems. These systems retain functional geomorphological and ecological components, but are subject to persistent pressures and structural constraints that limit their overall performance. As a result, a small number of highly preserved sites does not offset the broader regional pattern of moderate condition.
The class-based structure of the EGDVI further demonstrates that similar overall values may arise from different combinations of drivers and constraints. Very high and high scores reflect not only geomorphological integrity, but also the cumulative influence of governance-related factors such as legal protection, conservation feasibility and scientific recognition. Conversely, moderate and low values may be driven by sustained human pressure, reduced sediment connectivity, or spatial fragmentation. This diagnostic capacity distinguishes the EGDVI from simple ranking approaches and enhances its relevance for management-orientated interpretation.
By explicitly incorporating indicators adapted to the microtidal, fetch-limited dynamics of the Black Sea, the EGDVI addresses a key limitation of many existing dune assessment and vulnerability indices developed primarily for macro- or mesotidal coasts. The framework’s modular structure, transparent weighting scheme and fixed class thresholds support repeatability in long-term monitoring and conceptual transferability to other low-energy or semi-enclosed coastal environments, provided that indicator thresholds are locally calibrated.
Beyond site comparison, the EGDVI functions as a diagnostic and decision-support tool, identifying priority areas for conservation, highlighting systems where preventative management may avert further decline and distinguishing sites where restoration or rehabilitation measures are likely to be most effective. The explicit inclusion of legal protection and scientific value strengthens the science–policy interface by ensuring that institutional recognition and research relevance are adequately reflected in conservation planning.
Current limitations relate primarily to data availability and to the need for calibration beyond the Black Sea region. Nevertheless, the EGDVI provides a robust baseline for adaptive management and long-term monitoring of dune systems. Future refinements through structured expert elicitation, the integration of time-series observations and the use of emerging mapping technologies, such as UAS- and LiDAR-based analyses, including machine-learning approaches, are expected to further enhance its analytical resolution and operational applicability.
In summary, the EGDVI represents a substantive methodological advance in coastal dune assessment by integrating eco-geomorphological conditions, anthropogenic pressures and governance dimensions into a single, coherent framework. Its application along the Strandzha coast demonstrates both its diagnostic capacity at the site level and its ability to provide a meaningful regional synthesis, offering a transferable model for the assessment and management of dune systems in other microtidal coastal environments.