How Landscape Permeability enhances railway land management

The extensive transformation of landscapes by human society has resulted in significant challenges for biodiversity and its management. Habitat fragmentation, the division of continuous habitat into smaller, isolated patches, disrupts ecological connectivity and restricts animal movement [rb.gy/e8hluz ]. Urban and transportation infrastructure, including railways, are major contributors to landscape fragmentation, creating physical barriers, causing direct habitat loss, and generating pollution, noise and vibration that disturb wildlife [rb.gy/mxvqyu ]. These disruptions can have cascading effects on animal populations, hindering access to essential resources, isolating populations and reducing genetic diversity, and impeding critical migrations.

The concept of Landscape Permeability

Landscape permeability refers to the ease with which animals can move across a landscape. The concept encompasses factors like the availability of suitable habitat, the presence of barriers, and the overall connectivity between different ecological zones. Understanding and improving landscape permeability is crucial for effective wildlife conservation, as this allows for essential movement for vital ecological processes [rb.gy/493seu ].

The importance of Landscape Permeability in the British railway context

Britain's extensive railway network exceeds 20,000 miles in length [rb.gy/wldbih ] and, by traversing diverse ecological and geological landscapes, has the potential to significantly fragment habitats and disrupt wildlife movement patterns. The nature and extent of the actual impact is under-recognised and poorly understood [rb.gy/mxvqyu ] but comprehending the specific ecological context of these landscapes and the permeability challenges posed by the railway infrastructure is crucial for developing effective mitigation and nature management strategies.

The concept of landscape permeability provides an approach and tool to tackle some fundamental questions in the context of GB railway management. What are the key challenges posed by railway infrastructure to wildlife movement? What are the existing approaches for assessing and improving landscape permeability? How might the railway infrastructure manager potentially apply these approaches in developing its sustainable land use practice?

Landscape Permeability and GB nature conservation policy

Landscape permeability in Britain encompasses factors such as the availability and connectivity of suitable habitats (e.g., woodlands, hedgerows, wetlands) alongside the presence and characteristics of human-made barriers, like transport infrastructure. High landscape permeability allows for the unhindered movement of diverse species, facilitating essential ecological processes like dispersal, migration, and predator-prey interactions.

Understanding and improving landscape permeability is crucial for wildlife conservation [rb.gy/39klsl ]. Key characteristics of habitat patches within the landscape, including their size, shape, and connectivity, alongside the density of the transport network, are critical factors for informing conservation strategies. These factors directly influence the ability of wildlife to navigate the fragmented landscape created by transport infrastructure.

The concept of landscape permeability aligns with several key policy areas of the British Government (at the time of writing), including:

• The 25 Year Environment Plan: this government plan outlines a long-term vision for improving the environment in the United Kingdom, with a goal of leaving it in a better state for future generations [rb.gy/v7l6p0 ]. One of the key objectives of the plan is to restore and create wildlife corridors, which aligns directly with the concept of landscape permeability
• The National Planning Policy Framework: The NPPF emphasises the importance of protecting and enhancing biodiversity and promoting ecosystem services [rb.gy/9uwyqp ]. Improving landscape permeability for wildlife movement aligns with these goals by ensuring healthy and resilient ecological networks
• The Greening Government Commitments: The GGCs set out policy actions for UK government departments and their agencies to take to reduce their impacts on the environment. A core tenet is deploying nature-based solutions and integrating biodiversity considerations into departmental operations [rb.gy/7qmv4k ]. Landscape permeability assessments offer a powerful tool to achieve these goals.?
• Nature Recovery Network: the emerging new paradigm for nature conservation in Britain is based around the concept of the Nature Recovery Network (NRN), which promotes a landscape-scale approach that prioritises restoration, connectivity, and collaboration. Landscape permeability is a key component of the NRN. See my full article on NRNs and the railway .

The concept of landscape permeability thus has a significant role to play within the UK policy framework for nature conservation. By integrating this concept into wider its land management practices, the GB rail owner can contribute to a more sustainable future for both transportation and wildlife.

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Understanding Permeability: Structure vs. Function

There are two main ways to understand landscape permeability: structural and functional.

• Structural permeability focuses on the physical connections between different parts of the landscape, like patches of habitat, and does not directly consider the specific behaviours or ecological needs of different animal species. This concept is closely related to ‘landscape connectivity’ [rb.gy/b94r8a ]. In many cases, the terms ‘landscape connectivity’ and ‘landscape permeability’ are used interchangeably. However, ‘landscape permeability’ has a broader scope, encompassing all potential connections, regardless of animal species.
• Functional permeability, on the other hand, focuses on how well animals can move through the landscape, and considers how different animal species react to specific landscape elements and how these elements are arranged. This type of permeability is typically used when discussing the habitat needs of specific species that serve as models for nature conservation efforts [rb.gy/ltol4f ]. In situations where detailed information about species' behaviour is unavailable, we can assess movement possibilities using structural permeability.

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The impact of Habitat Fragmentation on Land Permeability

The main driver of reduced landscape permeability is habitat fragmentation - where large habitats are broken up into smaller, isolated patches. These fragmented patches gradually lose their ability to support the wildlife they once did. In Britain, fragmentation often happens because of changes in how land is used, particularly on the edges of its (semi-) natural areas [rb.gy/8sx4og ]

The ease with which animals can move between these patches depends on how similar the surrounding areas are to their natural habitat. For example, animals are more likely to cross boundaries between natural habitats, like woodland, than they are to cross artificial barriers like railway lines or urban areas. [rb.gy/d5pxgb ].

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Landscape Connectivity: corridors and movement

Landscape connectivity is crucial for wildlife conservation and refers to the network of pathways that allow animals to move between different natural areas [rb.gy/b94r8a ].

From the perspective of landscape ecology, a model called the ‘patch-corridor-mosaic model’ (Figure 1) helps us understand this concept [rb.gy/ps12jd ]. In this model, a corridor is a specific area that connects separate wildlife habitats and allows animals to move between them. These corridors are typically long and narrow, like a ribbon through the landscape.

However, corridors can also encompass wider zones called ‘connectivity areas’. These areas are important for maintaining healthy ecological processes and providing safe passage for a wider range of species by reducing the impact of barriers [rb.gy/vizy98 ].

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Existing approaches to Landscape Permeability assessment

Understanding landscape permeability requires different approaches depending on the scale and focus of the study. Three main approaches are evident from scientific studies, each with its own definition and assessment methods:

1. Species Approach

This approach focuses on the specific needs of individual animal species within a particular study area [e.g rb.gy/hmsu2a ]. Here, permeability is assessed in terms of:

• Species Movements: How animals move within the landscape, considering their behaviour and ecological requirements.
• Barriers: Identifying factors that hinder movement, such as roads, urban areas, or noise pollution.
• Population Viability: The impact of landscape fragmentation on the health and sustainability of animal populations.

This approach is useful for developing targeted conservation strategies for specific species. Methods of assessment include:

• Species Distribution Modelling: Identifying areas with suitable habitat characteristics for a specific species.
• Movement Tracking: Using radio telemetry or GPS collars to monitor animal movements and identify barriers.
• Habitat Suitability Modelling: Predicting the likelihood of a species using a specific habitat patch based on ecological requirements.

The main strength of the species-approach is that targeted information can be generated for specific conservation priorities. The main disadvantage is that the approach can be time-consuming and resource-intensive for multiple species.

?2. Landscape Connectivity Approach

The Landscape Connectivity approach analyses the overall structure and connectivity of the landscape to assess permeability for a wider range of species. Application focuses on the physical characteristics of habitat patches and their arrangement within the landscape [rb.gy/0pietq ].

Key aspects include:

• Landscape Structure: Analysing the characteristics of different habitat types (e.g., woodland, wetlands) and their arrangement within the landscape.
• Landscape Metrics: Using quantitative measures like patch size, shape, and edge density to quantify landscape structure. (See Table 1 for examples)
• Corridors: Identifying and evaluating the role of linear landscape elements (like rivers or hedgerows) that connect fragmented habitats.

Remote sensing and geospatial modelling play a crucial role in this approach. Methods of assessment include:

• Landscape Metrics: Using quantitative measures like patch size, shape, and edge density to quantify landscape structure (Table 1).
• Remote Sensing: Analysing satellite imagery to identify and map different habitat types and their spatial distribution.
• Connectivity Modelling: Identifying potential corridors and assessing their functionality for different species.

The main advantage of the approach lies in the provision of a broader understanding of landscape-level factors affecting permeability. The main disadvantage is that the approach may not capture the specific needs of individual species.

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3. Landscape Management Approach

This approach focuses on practical measures for improving permeability within existing infrastructure and land-use patterns, emphasising the planning and management of ecological networks that connect fragmented habitats [rb.gy/hrwvas ]:

• Ecological Network Planning: Identifying and protecting a network of core habitat areas and connecting corridors within a defined territory.
• Optimising existing infrastructure: Retrofitting existing infrastructure like railway bridges and under-track culverts to facilitate animal movement.
• Collaboration: Working with third parties to create wildlife corridors and enhance habitat connectivity across fragmented landscapes.

This approach is crucial for translating scientific understanding of permeability into practical conservation actions. Methods of assessment include:

• Gap Analysis: Identifying critical gaps in existing ecological networks that hinder animal movement.
• Cost-Benefit Analysis: Evaluating the costs and benefits of potential mitigation measures like wildlife crossings.
• Stakeholder Engagement: Collaborating with land managers, transportation agencies, and local communities to implement practical solutions.

A key benefit of this approach is the provision of a framework for translating scientific knowledge into practical conservation actions. However, implementation requires significant collaborative effort and the capability to effect meaningful compromise among different stakeholders.

By combining the three approaches - species; connectivity; and landscape management - railway land managers and their collaborators can develop comprehensive strategies to assess and improve landscape permeability for wildlife in the context of railway management and other infrastructure projects. This combined approach allows for targeted species protection, informed landscape management, and practical solutions to mitigate the fragmenting effects of infrastructure on wildlife movement.

Application of Landscape Permeability assessments to enhance railway biodiversity

Landscape permeability assessments offer a suite of methodologies to evaluate the ecological impact of railways and inform strategies for mitigating fragmentation and achieving biodiversity net gain:

Species Approach - focuses on understanding the specific movement patterns and habitat requirements of focal species of conservation concern. Targeted studies can employ static camera trapping or more dynamic radio telemetry or Global Positioning System collars to track animal movements and identify potential barriers posed by railway infrastructure. Species distribution modelling can further identify core habitat areas and potential corridors crucial for maintaining population connectivity. Habitat suitability modelling can then inform mitigation measures such as the creation of wildlife underpasses or the planting of specific vegetation for cover.

Metrics employed in this approach would focus on population size and trends, habitat use patterns, and the successful use of mitigation features by target species. Regular reporting on these metrics can be integrated into other biodiversity assessments, demonstrating the effectiveness of mitigation efforts for specific species populations.

Network Rail Southern Region has completed pilot work into the utilisation of remote sensing habitat data for ecological connectivity modelling. The aim was to investigate the use of habitat connectivity modelling to highlight key or more sensitive areas with potential ecological constraints with regards to protected species within the rail network.

?As part of the study, alternative methodologies were investigated with the objective of more efficiently predicting ecological constraints for the benefit of improving cost control and reducing risk. Of most promise was the application of remote-sensing methods in producing Phase 1 habitat maps over large stretches of the network and by using known habitat associations of key protected species to predict key ecological networks within the railway environment.

The total study area extended over approximately 112 miles of railway line and covered a land area of over 70 square miles. Habitat mapping was produced at 10m resolution using remote-sensing imagery produced during the European Space Agency earth observation mission: SENTINEL-2. Eight sections of the railway network, ranging from 9 to 18 miles in length, were identified within Kent and Sussex Routes as target areas.

For the final output, additional fine scale map elements, such as the presence of roads, railways, major and minor watercourses/bodies and priority habitats, were derived from readily available open-data sources and combined with the remote-sensing data. Twenty-seven different habitat classifications were identified within the target areas, including 10 categories that have the potential to support priority habitat types. ?Connectivity analysis was then conducted utilising the habitat mapping data for three separate species groups (Figure 2):

• Great Crested Newt;
• Hazel Dormouse; and
• Vesper bat species.

Within this process, least-cost path and circuit theory modelling methods were employed to produce least-cost pathways and probability mapping for each taxon between identified ‘source’ patches of optimal habitat.? ?Model parameters were derived from recent scientific literature and industry standard mitigation guidelines and enabled the identification of potential ecological networks within the landscape. Using the results, a relative ‘risk’ factor was assigned to each habitat area located within 50m of the railway line. Risk factors were categorised as high, moderate, low and negligible and represent the potential risk of impacts to the conservation status of local populations for each species group that may arise following significant disturbance.?

Risk areas for all three taxa were identified within lineside areas of all target areas, ranging from 4-55% of lineside habitats. For example, the Robertsbridge to Hastings line in Sussex was highlighted as a key area within the landscape with over 25% of lineside habitats assessed as ‘high’ risk for all three taxa.?

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Landscape Connectivity approach - provides a broader perspective on the ecological impact of railways by analysing landscape structure and connectivity. Landscape metrics, such as patch size, shape complexity, and edge density (Table 1), would be used to quantify the level of fragmentation caused by the railway network. Remote sensing data can be employed to monitor changes in habitat cover over time, allowing for the assessment of the long-term impact of railway operations and the identification of opportunities for habitat restoration. Connectivity modelling can then be utilised to identify potential wildlife corridors and prioritise areas for habitat restoration or the creation of new connections.

Metrics employed in this approach focus on changes in landscape metrics over time, improvement in connectivity for various species groups, and the area of restored habitat. Data on landscape-scale habitat connectivity and fragmentation trends can strengthen habitat-based reporting by providing a broader context for the impact of mitigation measures.

Network Rail commissioned the UK Centre for Ecology & Hydrology (UKCEH) to analyse the national Land Cover Map and ancillary spatial datasets to produce maps of habitat connectivity indices for four key habitat groups (woodland, heathland, semi-natural grassland and wetland) within a 1km buffer surrounding the railway estate [rb.gy/5mjenc ] (Figure 3). This data is now hosted in the railway infrastructure manager's geospatial system.

The dataset facilitates more holistic lineside habitat management and foster partnership working with lineside neighbours and stakeholders. Identifying the relative ‘connectedness’ of an individual site to key habitats is an important part of determining its relative priority for management intervention actions – which are organised around the categories of Conserve Habitat, Enhance Habitat, Restore Habitat and Transform Habitat.

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Landscape Management approach - emphasises practical, implementable solutions for mitigating fragmentation within existing infrastructure and land-use constraints. Gap analysis can be used to identify critical gaps in the ecological network that hinder animal movement across the railway estate. Cost-benefit analyses can then be conducted to evaluate the feasibility and effectiveness of potential mitigation measures like wildlife crossings (underpasses, overpasses) or green bridges. Stakeholder engagement with neighbouring landowners and conservation organisations is crucial for establishing ecological networks that connect railway lands with surrounding habitats.

Metrics employed in this Landscape Management approach focus on the number of implemented mitigation measures (e.g. wildlife crossing features) and participation in collaborative conservation initiatives. Documentation of these efforts strengthens biodiversity management and enhancement reporting by showcasing the railway owner commitment to broader landscape-scale conservation goals.

Network Rail Southern Region engaged with Chichester District Council (CDC) to facilitate cross-railway movement for priority species of animal on the Chichester Strategic Wildlife Corridor project:?

• CDC completed activity to identify and map safeguard wildlife corridors that can serve to sustain and enhance local biodiversity, in particular those that can improve connectivity between the nationally important South Downs National Park (SDNP) and the Chichester Harbour Area of Outstanding Natural Beauty (AONB), a north-south migration across the railway.
• Southern Region and CDC collaborated to address the recognised concern that the railway corridor has potential to both act as a barrier and facilitate the movement of animal (and plant) species across the area.
• Seven strategic locations were identified by CDC that interface with the rail network where ecological enhancements can raise the quality of connectivity to better support and sustain the ecology of the districts and wider area over the long term, these choices were informed by connectivity mapping.
• Focal species for the programme included: woodland bats, water voles, barn owls, dormice, farmland birds and Lepidoptera. Opportunity mapping for these species identified a suite of potential enhancements including habitat enhancement and planting, hedgerow creation, repurposing of redundant railway buildings, fish ladder and dormouse bridge installations.
• The main vegetative works were completed relatively quickly; artificial feature installation proved more costly and complex than initially anticipated and work continues to secure necessary permissions and an improved cost:benefit profile (in particular for the installation of a wildlife bridge spanning the rail line).
• Local nature conservation groups were engaged to facilitate monitoring of movements across the railway, utilising secure compounds to install monitoring equipment such as remote bat detectors and camera traps.

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Laying connecting tracks between Landscape Permeability and Biodiversity Net Gain

The UK Government has mandated the GB rail manager to deliver a net gain in biodiversity by 2040 [rb.gy/e0um2l ]. Landscape permeability assessments offer a valuable tool to enhance the effectiveness of net gain strategies. The Net Gain approach typically employs habitat units as a metric to quantify biodiversity loss and gain associated with development projects [rb.gy/jwi2mg ]. Permeability assessments, on the other hand, provide insights into how well animals can move through the landscape, which is crucial for maintaining healthy populations and ecosystem function.

By integrating permeability assessments into Net Gain planning, the GB rail manager can:

• Identify priority areas for habitat creation and restoration: landscape metrics and connectivity modelling can help identify areas where habitat restoration or creation would be most effective in improving permeability and supporting wider species movement.
• Enhance the functionality of mitigation measures: permeability assessments can inform the design and placement of mitigation measures like wildlife crossings, ensuring they effectively connect fragmented habitats and facilitate animal movement.
• Promote long-term biodiversity benefits: understanding how landscape permeability influences species movement patterns allows for the development of BNG strategies that not only increase habitat units but also promote long-term population viability and ecosystem resilience.

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Conclusion: take the track towards Permeability-informed railway land management

Habitat fragmentation caused by urban and transportation infrastructure poses a significant threat to wildlife connectivity and ecosystem health. The concept of landscape permeability plays a critical role in mitigating negative impacts. Furthermore, existing approaches to landscape permeability assessment - the Species, Landscape Connectivity, and Landscape Management approaches - can be effectively applied within the context of railway management.

Integrating permeability assessments into Biodiversity Net Gain strategies will strengthen railway efforts to manage its estate and lineside for wildlife. Permeability assessments provide valuable insights beyond simple habitat unit quantification, allowing for targeted habitat restoration, optimised mitigation measures, and long-term biodiversity benefits.

Next stops on the journey towards permeability-informed railway land management should then include:

• Prioritise landscape permeability assessments: integrate landscape permeability assessments into all stages of railway planning, construction, and operation.
• Develop permeability-focused BNG strategies: utilise permeability assessments to inform Biodiversity Net Gain strategies, ensuring they go beyond habitat unit targets and promote long-term ecological benefits.
• Collaborate for connectivity: work collaboratively with conservation organisations, landowners, and local communities to establish and maintain ecological networks that connect fragmented habitats across the railway landscape.

By embracing a permeability-informed approach to railway land management, the GB rail manager can play a leading role in fostering a more sustainable railway infrastructure. This approach balances essential transportation needs with the critical goal of maintaining healthy and interconnected ecosystems, ensuring a future in which the railway coexists harmoniously with thriving biodiversity.

Views in this article represent the author’s personal opinions only.