Open Mosaic Habitats on Previously Developed Land BNG Units
High
Urban
Trusted by Developers and Landowners
What are Open Mosaic Habitats on Previously Developed Land?
Open Mosaic Habitats on previously developed land are brownfield sites where disturbance, bare substrates, and early successional vegetation create a structurally diverse mosaic. The habitat supports specialised flora and invertebrates that depend on skeletal soils, bare ground, and pioneer plant communities.
The mosaic typically includes bare ground, ephemeral and short perennial vegetation, flower-rich open grassland, scrub patches, and occasional wet features.
Why It Matters for BNG
Open Mosaic Habitats deliver high distinctiveness units and are explicitly flagged in the Statutory Biodiversity Metric as difficult to recreate. Losses require like-for-like or better replacement.
Learn more about BNG for landowners →
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Where You'll Find It
Open Mosaic Habitats occur on brownfield sites, concentrated in urban and post-industrial areas. Key locations include former industrial land, rail yards, derelict sites, old airfields, landfill caps, quarries, and spoil heaps where disturbance history and substrate characteristics persist.
The habitat requires a minimum patch size of 0.25 hectares. Sites must have a known history of disturbance or clear evidence of soil removal, re-profiling, or severe modification such as made ground, spoil, or rubble.
Soil & Site Requirements
Open mosaic habitats favour skeletal soils with low nutrient status and varied substrates. Sites typically contain made ground, rubble, spoil, or heavily disturbed mineral soils with poor fertility. Bare ground, loose substrates, and micro-relief are essential features.
Drainage is typically free-draining to seasonally waterlogged, with small pools or wet hollows contributing to habitat diversity. The substrate must support early successional communities while preventing the site reverting to uniform grassland or dense scrub.
How New Open Mosaic Habitats on Previously Developed Land Is Created
Inputs
• Retain or create skeletal soils with low nutrient status
• Use made ground, rubble, spoil, or mineral subsoils without topsoil import
• Avoid amenity seeding or fertile topsoil application
• Ensure minimum patch size of 0.25 hectares
• Create varied micro-relief and substrate types
• Retain or introduce small pools or wet hollows where appropriate
• Allow natural colonisation from nearby brownfield sites
Management
• Maintain low-level disturbance to arrest succession
• Retain bare ground and loose substrates
• Control dense scrub or rank grassland through rotational clearance
• Avoid fertiliser application or nutrient enrichment
• Monitor invasive species and control to less than 5 percent cover
• Prevent conversion to standard amenity greenspace
Landscape
• Position creation adjacent to existing brownfield sites or urban ecological networks
• Link Open Mosaic Habitats to support invertebrate and reptile movement
• Locate where long-term disturbance regimes can be maintained
• Avoid sites where development pressure will force intensive landscaping
How Existing Open Mosaic Habitats on Previously Developed Land Is Improved
Inputs
• Retain or restore bare ground, rubble, and varied substrates
• Remove amenity topsoil or re-seeding that has enriched nutrient status
• Reintroduce skeletal soils or made ground where fertility has increased
• Control invasive species through targeted removal
Management
• Use rotational disturbance, scrub clearance, or light grazing to arrest succession
• Maintain multiple early successional elements including bare ground, ephemeral vegetation, and scrub patches
• Prevent uniform grassland or dense scrub from dominating through periodic intervention
• Avoid fertiliser, amenity mowing, or landscaping that homogenises the mosaic
Landscape
• Link open mosaic habitats with nearby brownfield sites or urban ecological networks
• Retain spatial variation and structural heterogeneity across the site
• Protect sites from conversion to standard amenity greenspace or intensive landscaping
• Manage at landscape scale to support invertebrate and reptile movement
Target Condition
Open Mosaic Habitats on previously developed land in their defined BNG condition should:
• Support multiple early successional elements including bare ground, ephemeral vegetation, flower-rich grassland, scrub patches, and wet features within the assessment area
• Demonstrate good structural heterogeneity at fine scale with varied substrates, rubble, micro-relief, and surface cracks
• Maintain pioneer elements and bare ground with succession arrested through ongoing disturbance or poor soils
• Contain characteristic early successional flora and, where recorded, notable invertebrate or plant assemblages
• Show minimal damaging modification with no extensive topsoil import, amenity re-seeding, or conversion to species-poor grassland
• Control invasive non-native plants to less than 5 percent cover
• Retain spatial variation forming a mosaic rather than uniform closed sward
The BNG Value of Open Mosaic Habitats on Previously Developed Land
• Distinctiveness: High
• Condition Potential: Can be maintained or enhanced through arrested succession, low-level disturbance, and protection from amenity landscaping
• Habitat Connectivity: Supports specialist brownfield flora and invertebrates, providing corridors within urban ecological networks
• Climate and Landscape Context: Stabilises disturbed ground, provides urban biodiversity refugia, and contributes to post-industrial landscape character
Species Typical of Open Mosaic Habitats on Previously Developed Land
Canopy or Primary Layer
• Sparse or absent tree cover
• Occasional birch (Betula pendula)
• Willow species (Salix spp.)
Shrub or Secondary Layer
• Bramble (Rubus fruticosus agg.)
• Gorse (Ulex europaeus)
• Broom (Cytisus scoparius)
Ground Flora or Understorey
• Oxford ragwort (Senecio squalidus)
• Coltsfoot (Tussilago farfara)
• Mosses and lichen crusts on bare substrates
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Frequently Asked Questions
What is Open Mosaic Habitats on previously developed land?
Open Mosaic Habitats on previously developed land is found on brownfield sites where disturbance and skeletal soils create a mosaic of bare ground, early successional vegetation, and structural diversity.
How is BNG measured here?
Condition is assessed using a bespoke urban Open Mosaic Habitats condition sheet in the Statutory Biodiversity Metric. Criteria focus on mosaic quality, arrested succession, species interest, and absence of damaging modification.
How can I achieve BNG?
Creation requires retaining or introducing skeletal soils, bare ground, and varied substrates without topsoil import or amenity seeding. Enhancement focuses on maintaining disturbance regimes, controlling succession, and preventing conversion to standard greenspace.
What is the BNG target condition?
Good condition requires multiple early successional elements, strong structural heterogeneity, arrested succession with bare ground retained, characteristic species assemblages, and minimal damaging modification or invasive cover.
What management is required?
Low-level disturbance to maintain bare ground and arrest succession, rotational scrub clearance, invasive species control, and avoidance of fertiliser or topsoil import. Management must prevent conversion to uniform grassland or amenity greenspace across the 30-year BNG period.
Exploring Other Habitats?
Line of Trees
A Line of Trees in BNG is a row or corridor of trees forming a clear linear feature in the landscape. It is made up of individual trees spaced closely enough to create a recognisable boundary or route through farmland, estates or river corridors. These lines often follow historic field edges, green lanes or trackways and can include banks or ditches alongside them.
Some lines are simple boundary features, while others hold greater ecological value because they contain mature or veteran trees, standing deadwood, cavities and other natural features that support birds, bats and invertebrates.
Native Hedgerow
A Native Hedgerow BNG habitat is a linear woody habitat where more than 80% of the shrub and tree cover consists of native species. Structurally, native hedgerows consist of a dense shrub layer commonly dominated by species such as hawthorn, blackthorn and hazel, often with standard trees including oak or ash emerging above the canopy.
Ecologically Valuable Line of Trees
An Ecologically Valuable Line of Trees is a high-distinctiveness linear habitat consisting of a continuous or near-continuous arrangement of trees over 20 metres in length, typically less than 5 metres wide between major stems, and distinguished by structural features that support specialist wildlife. Unlike standard lines of trees, this habitat includes at least one tree with veteran characteristics or natural ecological niches such as cavities, standing or attached deadwood, ivy cover or loose bark.
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