Mountain environments cover only about 25% of the total land area on the globe, but are shelter to over 85% of the planet’s species of, for example, amphibians, birds and mammals, many of them being restricted to mountains. Mountains play a multitude of roles for Earth’s biodiversity and influence surrounding lowlands through biotic interchange, changes in regional climate and nutrient runoff (Rahbek et al. 2019a, 2019b). They occur in half of the world’s biodiversity hotspots (Jacobs et al. 2021).

Climate change is affecting the mountain ecosystems at a faster rate than other terrestrial ecosystems (Jacobs et al. 2021) and temperature rises tend to be positively correlated with elevation (Pepin et al. 2015) and is expected to be more prevalent in the northern latitudes (Nogués-Bravo et al. 2007). The Carpathian Mountains are included in this trend, being exposed to multiple other stressors besides climate change that can affect the exceptional biodiversity values present here, especially the rapid expansion of LTI and other types of infrastructure.

The Carpathian ecoregion (Fig. 1) covers 209,256 km² (CERI 2001) and is shared by seven countries: Czech Republic, Slovakia, Poland, Hungary, Ukraine, Romania and Serbia. The studies on climate change affecting biodiversity in the Carpathians are scarce (Gurung et al. 2009; Werners et al. 2014a, 2014b; Hlásny et al. 2016; Kruhlov et al. 2018) and the combined effects of both climate change and habitat fragmentation due to LTI development has not been addressed and quantified yet.

Figure 1.

The Carpathian ecoregion.

Our broader focus on the Carpathian ecoregion is relevant in the context of large carnivores’ conservation, considering their need for extensive territories on one hand and, on the other, of LTI development which is more prevalent in the lower lands of the Carpathians.

Thanks to their exceptional natural values, including a great variety of endemic plants and animals, but also vulnerability, the Carpathians are included in WWF’s “Global 200” list of major ecoregions in need of biodiversity and habitat conservation (WWF 2001).

More than 60,000 native species, excluding microorganisms, are estimated to be present in the Carpathians (UNEP 2007). The Carpathians are home to approximately 4,000 vascular plants (Tasenkevich 1998), 35,000 invertebrate species, mainly insects, soil mites and spiders and over 500 vertebrate taxa, including mammals, nesting birds, amphibians, reptiles and fish and lampreys (UNEP 2007).

Three out of the five large carnivore species from Europe are present in the Carpathian ecoregion, namely the brown bear (Ursus arctos), grey wolf (Canis lupus) and the Eurasian lynx (Lynx lynx) (CERI 2001; UNEP 2007). Chapron et al. (2014) estimated 7,200 brown bears, 3,000 grey wolves and 2,300–2,400 Eurasian lynxes. Currently the overall size of these large carnivore populations in the Carpathians might be higher as a result of different conservation efforts and projects implemented in the region, as well as of favourable legislative framework at the EU level. Considering that these species are sensitive to habitat fragmentation caused by LTI (Proctor et al. 2012; Bischof et al. 2017; Finďo et al. 2018) and need extensive territories to satisfy their needs, concrete and intensive conservation efforts and harmonised management measures need to be put into action in the Carpathian ecoregion in a concerted way (Papp et al. 2020).

The Carpathians have a length of 1,500 m, an average altitude of 850 m, the highest parts being in the northwest and south, with the greatest elevation in Slovakia, 2,655 m (UNEP 2007).

Rising temperatures have been recorded in all seasons for the period 1961–2010, with substantial warming of up to 2.4 °C in summer seasons and the model projections suggest a future temperature increase of up to 1.8 °C for 2021–2050 (EEA 2017).

The Carpathians are an important water source for three major rivers, namely the Danube and Dniester, flowing into the Black Sea and the Vistula River, flowing into the Baltic Sea.

The Carpathians are not only home to wildlife, but also to over 17 million people living in both small remote villages and major cities (UNEP 2007).

As a result of the political transformation of 1989, accelerated changes in land-use and land-cover started to occur in Central and Eastern Europe, especially due to profound changes in agriculture, improvements in people’s welfare, growth in the tertiary sector and migration from rural to urban areas (Turnock 2003). Farmland abandonment increased in this period most probably in relation to institutional changes and restructuring of property rights (Munteanu et al. 2017). In addition, farmland abandonment in the Carpathian region threatens cultural landscapes and their associated biodiversity, although this can, in turn, increase carbon sequestration (Kuemmerle et al. 2008).

The first European nature conservation convention, the Bern Convention, signed in 1979, is the European contribution to the sustainable conservation of the world’s biodiversity. The Bern Convention developed the Emerald Network, a group of selected natural areas hosting crucial and threatened biodiversity in Europe (CoE 2021).

The contribution of EU member states to the pan-European Emerald Network is represented by the creation and management of the Natura 2000 Network (European Commission 1992, 2009), which is the largest coordinated network of protected areas in the world (EEA 2021). However, the Natura 2000 Network is only applicable in the EU member states, meaning that, in the Carpathian region, it is the main conservation tool in Czech Republic, Slovakia, Poland, Hungary and Romania (Fig. 2). A total of 1,178 Natura 2000 sites were designated by these countries in their Carpathian Mountain area. In the other two non-EU Carpathian countries, Ukraine and Serbia, the Emerald Network is the key conservation instrument (Fig. 2), having 49 Emerald sites designated in their Carpathian area.

Figure 2.

Natura 2000 and Emerald sites and transport network (motorways and roads) in the Carpathians.

The European Commission (2021a) also promotes the conservation of the five large carnivore species found in Europe and its guiding documents are used by the Carpathian countries to improve their conservation efforts of the three species that are present in the area and to develop national action plans.

The EU’s Biodiversity Strategy for 2030 (European Commission 2021b) is favouring both large carnivores and ecological connectivity conservation. The EU Strategy on Green Infrastructure is another EU-wide strategy relevant in the context of ecological connectivity and sustainable transport development.

The Convention on Environmental Impact Assessment (EIA) in a Transboundary Context or the ESPOO Convention, adopted in 1991, is another important legislative instrument. Given that seven nations share the Carpathian Mountain range and that large infrastructure projects including LTI are often developed between countries as part of different major transport corridors of international importance, the ESPOO can represent a valuable tool when mitigation measures, for instance, are not properly planned by a certain country, especially as a non-EU country.

The most important transport related policy of the European Commission (2021c) is the Trans-European Transport Network (TEN-T), directed towards the implementation and development of a Europe-wide network of roads, railway lines, inland waterways, maritime shipping routes, ports, airports and rail-road terminals. Three of the nine core transport network corridors are crossing the Carpathian area: Baltic Adriatic, Orient/East Mediterranean and Rhine-Danube (European Commission 2021d). The existing LTI, developed within these large transport corridors, is impacting to some extent the ecological connectivity in the Carpathian region. In the eastern part of the Carpathians, especially in Romania, the LTI, corresponding to the Orient/East Mediterranean and Rhine-Danube transport corridors, is still under development and concrete measures have to be taken in order to either avoid, mitigate or ultimately compensate for the potential environmental impacts.

The only multi-level governance mechanism covering the whole of the Carpathian area is the Framework Convention on the Protection and Sustainable Development of the Carpathians (Carpathian Convention), adopted in 2003 by the seven parties. It has two specifically relevant protocols to our topic: Protocol on Conservation and Sustainable Use of Biological and Landscape Diversity and Protocol on Sustainable Transport (UNEP Vienna Programme Office 2021). These two protocols set basically the framework for conserving biodiversity and maintaining ecological connectivity, while developing transport infrastructures in the Carpathians. In addition, the parties to the Carpathian Convention adopted the International Action Plan on Conservation of Large Carnivores and Ensuring Ecological Connectivity (Papp et al. 2020; UNEP Vienna Programme Office 2020), which is framing a unique and innovative example of a participatory and coordinated effort at transboundary level for implementing a population-based conservation of large carnivores, benefitting not only the Carpathians and the broader Danube Region, but also other regions in Europe and beyond. The second strategic objective of the Plan is to “Prevent habitat fragmentation and ensure ecological connectivity in the Carpathians” and contains a major action for mainstreaming biodiversity into transport planning and development.

Biodiversity and connectivity conservation is a priority action also under the macro-strategy European Strategy for the Danube region (EUSDR 2020), the Carpathians being part of the wider Danube region.

Since joining the EU, Czech Republic, Slovakia, Poland, Hungary and Romania gradually harmonised their national legislations with the EU regulations. Some of these countries (e.g. Czech Republic) have a higher level of compliance with EU legislation than others (e.g. Romania), at least from a transport and environmental point of view. On the other hand, the non-EU countries, namely Ukraine and Serbia, are preparing for this harmonisation as part of their EU accession process. This means that, in the Carpathian region, there are consistent differences in the national legislation from EU to non-EU countries, but there are also differences even within the same country category.

In all Carpathian countries, there is relevant nature conservation related legislation which provides the framework for conserving ecological corridors. However, all countries are lacking in official methodologies for the identification and designation of ecological corridors, which, in practice, makes connectivity conservation difficult and often ineffective.

Czech Republic and Slovakia are the most advanced countries in terms of connectivity conservation, where it is actually possible to protect ecological corridors and to maintain landscape connectivity through specific national nature conservation instruments.

In Hungary and Poland, there are also regulations regarding ecological corridors; however, the binding framework related to them is not well established, meaning that there are no uniform rules to determine corridors and there is no consistent network of corridors at the national level.

In Romania and Serbia, the protection and management of ecological corridors is not yet clearly defined, even though there are provisions related to the ecological network, including definitions. In practice, there are no legal obligations and restrictions imposed to secure ecological corridors. The only country in the Carpathians with a dedicated law on the preservation of the ecological network is Ukraine; however, its practical implementation is facing difficulties due to conflicting sectoral legislation or lack of dedicated funding for the identification of ecological corridors.

Papp and Berchi (2019) collected further information on the most relevant pieces of legislation at national levels in all the seven Carpathian countries.

In the absence of officially designated corridors, clear legal obligations and specific binding management measures to secure ecological connectivity, LTI development will remain one of the greatest threats to the integrity of natural habitats and functionality of existing ecological corridors in the Carpathians.

The Strategic Environmental Assessment (SEA), Environmental Impact Assessment (EIA) and Appropriate Assessment (AA) can additionally contribute to a higher level of biodiversity and ecological connectivity protection by assessing the impact of different strategies, plans, programmes or projects on them.

The Directive on the assessment of the effects of certain plans and programmes on the environment (European Commission 2001), also known as the “SEA” Directive, requires and regulates the environmental assessment of certain plans and programmes which are likely to significantly harm the environment, for example, transport master plans. In the context of TEN-T further development and general transport planning, it is important to reconcile the descriptive and analytical aspects of the SEA and, in this respect, Fischer (2006) proposed a generic SEA framework for evaluating practice and developing further guidance.

The EIA Directive (European Commission 2014) on the assessment of the effects of certain public and private projects on the environment, requires environmental assessments for certain projects like LTI development, which can have a significant impact on the environment by virtue, before a development consent is given by the competent national authority.

AA is required by the Habitats Directive when a plan or project, either alone or in combination with other plans or projects, might impact a Natura 2000 site. The different LTI projects generally have an impact on Natura 2000 sites or other protected area categories, especially if developed in mountain areas like the Carpathians where there are several protected plant and animal species. AA is thus a prerequisite and shall constitute an integral part of SEA and EIA procedures.

The main issue in implementing the SEA, EIA or AA in the Carpathian countries is represented by the fact that the cumulative effect is not calculated properly or not at all. Several assessments of the effects of LTI on biodiversity conclude that there is no significant harm or provide a basic set of minimum mitigation measures and do not consider, for example, nearby electric fences, European road, railway and river (Fig. 3). In Romania, for instance, the ecological corridors are not identified and designated, so it is difficult to consider them in the planning process, which leads to an increase in habitat fragmentation.

Figure 3.

Cumulative impact of a highway sector between Turda and Aiud in Romania b Mureș River c railway d European road E81 and e electric fence used to keep wildlife away from the agricultural field, on the permeability of the landscape, not assessed.

In all Carpathian countries, based on previous experience in the construction of LTI, especially motorways, the greatest problems are seen in assessing the impact of the transport corridor on sustainable land development. In the Czech Republic, a key problem that is addressed is the impact of the new infrastructure on the environment, in particular, the elimination of health impacts (noise and vibrations, air pollution), the location of the linear construction in the landscape and the solution to the issue of fragmentation, the interruption of ecological corridors.

The benefits of taking an active and conscious part in shaping local spatial policies are generally not properly explained in the Carpathian countries and, therefore, low social awareness in the area of spatial planning and environmental protection can be observed, especially in Poland and Romania.

The problem of habitat fragmentation due to LTI has been underestimated in the Carpathian countries for a long time. In Slovakia, for instance, there are just a few studies aiming at the identification of core areas and ecological corridors. There is, indeed, an EIA analysis carried out during a landscape planning process, but it is rather a theoretical analysis lacking in reliable field data and validation, which is basically common to all Carpathian countries, excepting to some extent, Czech Republic. In Hungary, to regulate or decrease the impacts of LTI on natural habitats, the alignment is chosen in the planning stage, based on the least number of most sensitive areas each alternative is crossing.

In Serbia, as well as in Romania and Ukraine, generally there are no comprehensive habitat and species distribution maps which could provide a sound basis for integrative planning of LTI.

In Ukraine, there are specific provisions and recommendations to construct wildlife crossing structures and fences along certain roads, but they largely remain as recommendations, not as obligations.

In the absence of clear commitments to identify and designate ecological corridors in the Carpathians, many mitigation measures are not properly designed and certainly not implemented in proper places. Moreover, the lack of harmonisation of cross-sectoral policies and strategies is also leading to increased fragmentation in the region.

Ecological corridors are an important component of functional ecological networks and they primarily connect wildlife habitats and improve the functional connectivity of landscapes. Ecological connectivity, as defined by CMS (2020) “is the unimpeded movement of species and the flow of natural processes that sustain life on Earth”. Connectivity is essential for supporting species’ movement for individual survival, mating, searching food and other resources, gene flow in metapopulations and for colonisation of new areas.

However, ongoing habitat fragmentation and loss continue to threaten such functions and cause decline of populations and even local extinction (Crooks et al. 2017; Westekemper et al. 2021). Wide-ranging species, such as large carnivores, are more likely to experience negative population-level effects of habitat fragmentation and to exhibit low tolerance for human activity (McClure et al. 2017).

The case of the Carpathian Mountains shows the importance of maintaining landscape connectivity on an international scale.

The ecological corridors keep landscapes permeable and one way to identify them is by the species-specific needs and the movement function they provide. Large carnivores naturally do not respect state boundaries or any other administrative or political frontiers; however, infrastructure and urban development is driven mainly by national strategies. The most efficient tool for maintaining landscape connectivity is the development and protection of ecological networks. In the case of the Carpathians, a robust supranational system of core areas and corridors is the proper solution.

Several projects and studies focused on identifying ecological networks and corridors in the Carpathians for large mammals, for example, the “Mapping conservation areas for carnivores in the Carpathian Mountains” (Salvatori 2004), “Potential habitat connectivity of the European bison (Bison bonasus L.) in the Carpathians” (Kuemmerle et al. 2011), “Identification and assessment of the potential movement routes for European bison in the North-East of Romania” (Deju 2011), “Creation of ecological corridors in Ukraine” (Deodatus et al. 2013), BioREGIO Carpathians project (Appleton and Meyer 2014) and Life Connect Carpathians (FFI 2019). No matter the selected focus species, the identification of ecological corridors used different methodologies, making the results non-comparable at the Carpathian level, sometimes not even at the national levels.

Our approach to identify the ecological network for large carnivores in the Carpathians (Papp et al., in prep.) (Fig. 4), was based on the habitat suitability models using the actual occurrence data of large carnivores (bear, wolf and lynx) and a set of environmental variables including abiotic, habitat and anthropogenic factors. According to the habitat suitability models, core areas and stepping stones were identified and their function in the Carpathians was discussed with local and national experts. At the same time, the resistance surface was derived from the habitat suitability model and fragmentation geometry was prepared in order to express landscape permeability for large carnivores. Finally, a connectivity model was prepared presenting a coherent network of core areas, stepping stones and corridors. This output was reviewed with experts and improved, based on their feedback in order to produce the final version of the pan-Carpathian ecological network. This is the first comprehensive ecological network projected at the Carpathian ecoregion level, offering a robust instrument for spatial planners and other stakeholders to identify from the early stages of planning different LTI or other large infrastructure projects, potential conflicts between economic projects and nature conservation. The intersection points between these two can be further explored and solutions tailored to allow both development and conservation.

Figure 4.

The ecological network for large carnivores in the Carpathians and the overlap with the transport network.

Another significant factor, which negatively influences ecological connectivity in the Carpathians, is increasing urbanisation and industrial development. The increasing human disturbance, especially around large cities and/or touristically attractive places, can also negatively influence wildlife, as well as natural habitats. This includes the use of 4×4 vehicles, jogging, biking and hiking, harvesting of non-timber products, hunting, skiing, the operation of ski lifts in the middle of protected areas etc.

Moreover, as a result of increasing intensive agriculture and large-scale forestry in many Carpathian countries, continuous and systematic loss of valuable large carnivore habitats is taking place.

The use of electric fences to prevent human-wildlife conflicts (e.g. to guard livestock, beehives, crops, orchards or properties, in general), although in principle an important and widely recommended conservation tool, can create a serious barrier effect, especially if deployed on a large scale.

The edge effect sometimes could possibly cause increased predation, increased mortality within corridors and the spread of invasive species and diseases. Some investigations confirm it to varying degrees (Haddad et al. 2015).

Last, but not least, climate change is also posing a serious, but hard to quantify threat at the moment to the Carpathian habitats.

During the railway reconstruction in the Beskydy Protected Landscape Area, eastern Czech Republic, two underpasses (Fig. 5A) were built. They meet the requirements to facilitate the movement of large carnivores. The permeability of the railway sections was improved, a fact that was confirmed by the sand belt monitoring and snow tracking of animals passing through the underpasses. Four ecoducts are currently under construction as part of the extensive modernisation of the D1 motorway between Prague and Brno as a contribution to defragmentation.

Besides some prolonged viaducts on some road sections, two green bridges exist in Slovakia. The first is connecting the High and Low Tatra Mountains (Fig. 5B). The second one is the so-called ACC (Alps-Carpathians Corridor) north of Bratislava that should enhance wildlife movements between Slovakia and Austria. This contribution to defragmentation started in 2016, being the first attempt in Central and Eastern Europe to build such a structure over an existing operating motorway.

Along the TEN-T network in Poland, several overpasses (green bridge-type crossings) that allow wildlife movement already exist. Moreover, bridges over watercourses are adapted to the migration/movement of animals. On the motorways, there are also structures for medium size animals, such as underpasses or culverts.

In Hungary, best practices refer to wildlife overpasses built over, for example, motorway M43 in south-east (Fig. 5C) or motorway M85 in the western part. Furthermore, several underpasses for medium-size animals, as well as noise, light-pollution and bird protection walls, have been built. Blue retro reflectors were also installed on odometers on Main Road1 in Hungary to reduce wildlife collisions (Fig. 5D).

As of today, there are no concrete examples of sustainable transport development in Ukraine, but there are intentions in this respect. Some decisions from the past can be considered as being sustainable, taking into account that they create conditions for permeability of motorways and railroads. They refer to the large bridges over Latorytsya River and the Beskydskiy Tunnel in the Carpathians, as well as numerous railroad culverts and bridges.

The first major transport infrastructure project in Romania that incorporated mitigation measures for ensuring connectivity within the landscape is the Lugoj-Deva highway. The original technical project was improved to include a system of solutions (i.e. tunnels, viaducts, green bridges) that allow the movement and dispersal of large carnivore species. Three green bridges have been built in total (Fig. 5E, F), two tunnels and three viaducts are expected to be realised according to the environmental permit.

There are no notable best practice examples in Serbia. At the moment, several highways are in the planning and designing process and possibilities/obligations for the construction of the migration/movement structures are explored; however, there is a perpetual problem of non-existing hard evidence of the ecological corridors at Serbian national level.

There are obviously many negative examples concerning the infrastructure development in the Carpathian region, even if they are not highlighted or properly documented.

For example, in the Czech Republic, the construction of four ecoducts in the southern and two that were built on the northern road circuit of Prague are very questionable. This is a suburban, very intensively used area, with high human activity. No endangered species can be expected to inhabit here or disperse through the road, which had a negative impression on public opinion about spending money on green bridges.

Zvolen–Kriváň section on R2 is a negative example from Slovakia. The express road has dramatic negative impacts on the movement of wildlife due to the absence of functional wildlife crossing structures. The road section completely isolates the valuable Poľana Mountain range, hosting the three large carnivore species, from the south of the country and further from Hungary.

The number, density and design of animal crossings is not optimal in Poland, not even in protected areas. The functionality of most passages for large and medium size animals is significantly limited by the structures’ poor management/maintenance or use of the surrounding areas by humans. One example is the viaduct for large mammals close to Nietoperek, where the inappropriate height is limiting the possibilities of the animals to move from one way to another.

Hungary has a relatively low number of wildlife passages (40 in total, as of 2010) and they are not evenly distributed with regards to the main identified wildlife corridors. Hungary’s largest viaduct is at Kőröshegy on the M7 motorway to the south of Lake Balaton. The necessity of this large viaduct was a topic of many debates at the end of the construction in 2007. In the proximity of the viaduct, a wildlife overpass was built in the correct location (leading out from a forest into a dirt road), but in a wrong way. It is basically not functional due to some technical mistakes/details that were overlooked. The monitoring of wildlife tracks revealed that deer and other species turned around.

In Ukraine, there are no dedicated wildlife crossings constructed at the moment and, generally, the movement needs of large mammals were not considered when LTI was developed.

Romania is another negative example where, due to the lack of an integrated approach in the case of Lugoj-Deva highway, a green bridge built in Brănișca area over the highway does not mitigate the negative effects of the adjacent existing county road and ends in the county road instead of passing it and leading the animals to the existing forest patch that borders the road.

In Serbia, there is a general belief amongst conservation groups that the development of LTI is done in a negative way, since the movement needs of animals are not properly addressed, partly because of the lack of ecological corridors designation and recognition. No dedicated wildlife structures have been built yet in Serbia.