Axion Solutions | Research, Digital & Environmental Consultancy

Executive Summary

Axion Solutions was commissioned by the Derry City & Strabane District Council (DCSDC) to deliver a critical assessment of the council’s estate: the 2025 Invasive Alien Species (IAS) Assessment of Green Spaces. This project forms the foundational step in the council’s Green Infrastructure Plan, providing a reliable evidence base to support future management, infrastructure planning, and ecological enhancement.

The commission addressed a significant environmental challenge: the widespread colonisation of aggressive non-native species across 37 council-managed sites. Axion delivered a comprehensive, district-wide intervention that combined:

District-scale field surveys covering parks, greenways, cemeteries, and riverside/landfill corridors.
Standardised GIS mapping of Schedule 9 species, quantifying infestation areas (m²) using a consistent spatial reference system.
A Traffic-Light Classification system (RAG) to prioritise sites based on the proportion of invasive coverage.
Targeted control recommendations and a structured management framework to restore ecological health.

The result is a high-accuracy spatial infrastructure that empowers the council to transition from reactive maintenance to a strategic, data-led restoration programme.

Strategic and Policy Context

DCSDC’s Green Infrastructure (GI) Plan aims to improve green and blue spaces to mitigate climate change, protect biodiversity, and provide essential ecosystem services. Maintaining the health of these spaces requires compliance with statutory requirements, specifically:

The Wildlife (Northern Ireland) Order 1985 (as amended): Mandating the management and prevention of spread for Schedule 9 species.
The Invasive Alien Species (Enforcement and Permitting) Order (NI) 2019: Governing the handling and disposal of contaminated materials.

To meet these goals, the council required a delivery partner capable of translating fragmented legacy data into a unified, procurement-ready dataset for long-term monitoring.

The Challenge: Mapping Across a Diverse Urban and Rural Estate

The project addressed the difficulty of managing invasive species across a fragmented delivery landscape.

Data Fragmentation: Prior to this commission, information was split between the 2018 EVO Ecology survey and other internal records, which often lacked consistent spatial references or exhaustive coverage.
Complexity of the Landscape: Sites ranged from small urban play parks with isolated occurrences to vast linear corridors (e.g., Foyle Valley Greenway) where infestations dominated riparian banks.
Rapid Growth and Spread: The aggressive nature of species like Himalayan Balsam and Japanese Knotweed required a current, time-boxed assessment to reflect real-world conditions before management could be tendered.
Operational Requirements: The council needed data that was "treatment-ready," allowing them to sequence control efforts based on risk and ecological sensitivity.

The 2018 EVO Ecology survey highlighted the scale and spatial variability of infestation across the estate. For example:

Foyle Park recorded an estimated 11,439m² of Himalayan Balsam (derived from a 57,197m² stand with 0.2 density factor), alongside Giant Rhubarb, Salmonberry, and multiple Japanese Knotweed occurrences.
Prehen Park contained an estimated 2,925m² of Himalayan Balsam in addition to multiple dense Japanese Knotweed clusters (including 80m² and 100m² recorded stands).
Riverside Walk (Strabane) exhibited repeated linear infestations of Giant Hogweed, Himalayan Balsam (up to 100m² recorded stands), and Japanese Knotweed along riparian corridors.
Waterside Greenway included significant Salmonberry coverage (estimated 2,619m² at 0.1 density factor), alongside Japanese Knotweed (including Lesser Knotweed records).
St Columb’s Park recorded multiple Himalayan Balsam stands ranging from 20m² to 200m² in close spatial proximity.

However, the 2018 dataset was largely point-based and site-specific, making it difficult to visualise cumulative site-level coverage or determine proportional infestation relative to total park area. This created a strategic gap between ecological observation and infrastructure-level decision-making.

The Project Process: A Structured Delivery Framework

Axion applied a four-phase, evidence-led workflow designed for efficiency and transparency.

Mobilisation and Familiarisation:
1. Confirming site access and reviewing legacy records
2. Desktop mapping of historical EVO Ecology GPS coordinates
3. Tiering sites (High, Medium, Low effort) based on historic infestation density and spatial clustering

The 2018 coordinate logs (including precise eastings/northings for sites such as Ballyarnett Country Park, City Cemetery, Marianus Glen, and Creggan Burn) were digitised and imported into QGIS to identify historic hotspot clusters prior to 2025 field mobilisation.

Field Survey and Data Capture:
1. Use of GNSS-enabled devices for high-accuracy polygon capture.
2. Mapping IAS stand polygons and individual observation points.
3. Geotagged photographic evidence for all priority stands.

Where 2018 records identified large or repeated infestations (e.g., multiple Japanese Knotweed records at City Cemetery ranging from 2m² to 40m²), these areas were prioritised for verification and re-survey to assess expansion, regression, or treatment impact over the seven-year interval.

Data Processing and Quality Assurance:
1. Consolidation of field logs into a unified Geopackage.
2. Polygon-based area calculation (m²) replacing density-estimate methodology.
3. Cross-referencing attibute data for taxonomic consistency.

Unlike the 2018 density-factor method (e.g., Himalayan Balsam at 0.2 density multipliers), the 2025 approach calculated true spatial footprint polygons, improving procurement accuracy and enabling direct year-on-year comparison.

Reporting and Handover:
1. Comprehensive GIS package for council integration.
2. Site summaries with priorities recommendations.
3. Excel species-area matrix with structured for tender documentation.

Historic 2018 estimated stand areas were retained within metadata fields, enabling longitudinal comparison and forming the first structured temporal IAS dataset for the district.

Quality Assurance and Procedural Rigour

Axion’s QA system ensured that 100% of spatial records were verified against photographic evidence and GNSS logs. Each deliverable underwent a multi-tier review process:

Data Integrity: GIS Analysts confirmed attribute consistency for species names, area calculations, and habitat context.
Spatial Validation: Verification that all polygons and observation points aligned accurately with OSNI basemaps and site boundaries.
Reporting Consistency: Site summaries were reviewed to ensure management recommendations were proportionate to the observed density and species behaviour.

This rigour ensured that the dataset met mandatory requirements for precision in identifying species, locations, and m² per site.

In addition, legacy EVO Ecology coordinates were spatially cross-checked against 2025 polygon extents to identify:

Confirmed persistence zones (e.g., Japanese Knotweed clusters at Ballyarnett Country Park).
Riparian spread corridors (e.g., Riverside Walk, Foyle Park).
Sites where density-estimated stands had consolidated into continuous polygon infestations.

This retrospective validation strengthened confidence in both datasets and formalised the transition from observational survey to infrastructure-grade spatial asset management.

Mapping and GIS: Structuring Strategic Action

The assessment turned raw ecological data into usable infrastructure through spatial analysis in QGIS.

Interactive Visualisation: Sites were categorised using a RAG system:
Red: Coverage exceeds 5% of total area (e.g., Strabane Canal at 6.3%).
Amber: Coverage between 0.5% and 5% (e.g., Bay Road Park at 0.7%).
Green: Coverage below 0.5% (e.g., Claudy Country Park).
Standardised Data Model: Each stand was attributed with species-specific metadata, habitat sensitivity scoring, and photo links, enabling the council to "time-travel" through the site’s history during future re-surveys.

Historic 2018 sites with high estimated stand areas (e.g., Foyle Park Himalayan Balsam; Waterside Greenway Salmonberry; Newtonstewart Recycling Centre Himalayan Balsam) were automatically flagged for higher risk classification pending 2025 validation. This enabled the council to move from species-by-species observation to proportional, estate-wide prioritisation.

The integration of 2018 point clusters into 2025 polygon mapping also enabled visualisation of longitudinal spread patterns along watercourses, particularly for Himalayan Balsam and Giant Hogweed, reinforcing the need for corridor-scale rather than site-isolated interventions.

Project Conclusions: Impact and Learning

The commission successfully transitioned DCSDC’s IAS monitoring from a reactive activity to a structured district-wide system.

Key Findings and Outcomes:

Dominant Species: Himalayan Balsam and Japanese Knotweed were found to be the most widespread, particularly along watercourses where seed spread is constant.
Priority Hotspots: Large green spaces and linear corridors (e.g., Ballyarnett Country Park, Foyle Valley Greenway) were identified as the highest management priorities due to extensive linear infestations.
Evidence-Based Engagement: Identifying dense infestations near infrastructure (e.g., Japanese Knotweed close to buildings at Strabane Council Offices) allows for urgent, targeted remedial action.
Procurement Readiness: By delivering a complete species–area matrix, Axion provided the council with the exact data needed to tender treatment contracts.

Longitudinal analysis demonstrates that several 2018 infestations (particularly Japanese Knotweed at cemetery sites and riparian corridors) have persisted over a seven-year period, confirming the resilience of established rhizomatous species and the necessity of multi-year treatment contracts rather than single-season interventions.

The comparison between 2018 density-estimated stands and 2025 polygon-calculated footprints provides the council with its first structured temporal benchmark for invasive species spread, containment, or regression.

Reflections and Long-Term Legacy

The project established a maturation point in DCSDC’s ecological stewardship. By treating IAS data as a living infrastructure, the council now possesses a durable asset that materially reduces the burden of coordination for environmental maintenance.

Restoration Framework: The data supports the replanting of treated areas with native species to enhance biodiversity and stabilise soil.
Community Integration: The mapping provides a platform for volunteer "Balsam Bash" events and public awareness campaigns.

Importantly, the integration of the 2018 EVO Ecology dataset ensures institutional memory is retained. Rather than superseding historic work, the 2025 assessment consolidates and enhances it—transforming fragmented point observations into a unified, district-scale ecological intelligence system.

The legacy of this work is a master spatial dataset that establishes a replicable model for future system-level land monitoring, ensuring that every intervention is supported by clarity, purpose, and lasting ecological impact.