What's Next for Invasive Non-Native Species Management and Why Does it Matter?

Emerging Invasive Non-Native Species (INNS)

Well known Invasive-Non-Native Species (INNS) are widely understood, however the threat of new and emerging INNS across the UK is real. 

This post focusses on species being considered for listing by the INNS GB non-native species secretariat; whilst the emerging list is not final and is entirely advisory, those mentioned currently make up the first cycle of the listing process. 

The plant species being considered are detailed below, including their prevalence and how they spread:

• Purple Pitcher Plant (Sarracenia purpurea): A carnivorous plant in the UK, typically found across the southern regions. Particularly favours nutrient-poor bog habitats and outcompetes native flora including Sphagnum moss. Spreads via a deep rooted horizontal growing rhizome system. 
  
  
• Giant Cane (Arundo donax): Introduced to gardens, favours riparian habitats that can form dense monocultures. It displaces areas of native vegetation and can increase the risk of flooding across these areas. This species is already formally listed as invasive under the Wildlife and Countryside Act Schedule 9 in Northern Ireland. The plant spreads via a network of rhizomes through creeping stems forming dense colonies known as canebrakes.
  
  
• Thicket shadbush (Amelanchier spicata): A species commonly used for it’s horticultural value, it can form dense thickets through dense suckers at the base of the plants which can shade out native species from establishing. It can spread from both distributed seeds and its lateral root system. 
  
  
• Chocolate Vine (Akebia quinata): This species can rapidly cover areas by forming dense mats which smother native species and can grow upwards of 40 feet. The species produces pods with seeds which are typically dispersed by birds. 
  
  
• Snake-bark maple (Acer rufinerve): An ornamental tree species known for its vibrant autumn colour and striped bark. This species can form dense shade-producing thickets which can reduce ground layer diversity of native species. They can propagate via numerous seeds allowing for it to disperse widely and quickly. 

- by Connor Tucker, Senior Landscape Manager, Warrington office.

INNS and Biodiversity Net Gain

In UK planning and environmental policy, invasive non-native species (INNS) are closely linked to Biodiversity Net Gain (BNG). This relationship is reflected in the Statutory Biodiversity Metric condition assessments, where the presence of INNS is considered within the scoring criteria for many habitat types.

Where INNS are identified during ecological site assessments, they are recorded as a negative factor for the relevant habitat type. Their presence can reduce the overall condition score, depending on how the habitat performs against the remaining criteria. For example, scrub containing INNS may fail to meet the requirements for moderate condition and may therefore be recorded as poor condition.

The management and treatment of INNS within a BNG scheme can improve habitat condition and increase the number of biodiversity units (BUs) generated by that habitat. In the example above, appropriate treatment to remove INNS from scrub habitat could help improve the baseline condition and support a higher target condition following intervention. Proactive INNS management can also help prevent their spread into new areas, or further spread within areas where they are already present.

Where INNS are recorded on a development site, suitable biosecurity measures should be implemented to prevent spread into other habitats, which could otherwise reduce their habitat condition and the sites overall habitat value.

BNG can support the treatment of INNS at a local level by incentivising habitat improvement through condition targets. This can increase a site’s BU value while helping developers and landowners meet the statutory requirement to deliver at least 10% biodiversity net gain for new development.

Where a development cannot meet its BNG requirements on-site, the sale of BUs through off-site solutions can provide funding for wider habitat enhancement. This can include targeted INNS management within BNG Habitat Banks, helping to address INNS across habitats and landscapes where funding or delivery opportunities may previously have been limited.



The long-term legacy of BNG is supported by a requirement for habitat management and monitoring for a minimum period of 30 years. This provides an opportunity for longer-term INNS treatment programmes where their management is required to achieve target habitat condition. It also enables continued oversight and monitoring of sites, whether INNS are currently present or there is a risk of future colonisation, supporting a proactive approach to their management.

- by Rick Tomlinson, Associate Landscape Manager, Warrington office.

For further information on our Land and Estate Management services, or to discuss invasive species or wider land management issues, please contact us and a member of our team will be in touch.