Invasion of the Non-Native Concrete Snatchers

Did you know that there are around 80 invasive non-native plant species regulated under Schedule 9, part II of the Wildlife and Countryside Act 1981 with another 40 new non-native species expected to become established in the UK by 2040? [1]. Here we discuss what these species are, what the implications are on land development and what the corresponding land remediation processes can involve.


The Joint Nature Conservation Committee (JNCC), a public body that advises the UK Government and devolved administrations on UK-wide and international nature conservation, identifies non-native species as those that have reached this country by “accidental human transport, deliberate human introduction, or which arrived by natural dispersal from a non-native population in Europe.” It includes all species that have found their way to our shores from the year 1500. [2] In addition to the JNCC, the Non-Native Species Secretariat has responsibility for helping to coordinate the approach to invasive non-native species in Great Britain, and their website provides a comprehensive set of tools and extensive information for those working to support the GB Invasive Non-Native Species Strategy. [3]


Many of non-native plants were transported to our island nation deliberately by well-meaning horticulturalists over the years, who brought them back from overseas to enhance the planting of their gardens and estates here in the UK. The most well-known of these are Japanese Knotweed, Giant Hogweed, Himalayan Balsam, Rhododendrons and Buddleia, but other lesser-known species such as Water Primrose, Floating Pennywort, Variable Water Milfoil and Parrot’s Feather are wreaking havoc in some parts of the UK.



Whilst some of these plant species may still be used within contained domestic settings, deliberate introduction into the wild is regulated under Section 14 of the Wildlife and Countryside Act 1981.


Due to previously uncontrolled releases, these species are now well established in the wild where they continue to pose a conservation threat to native biodiversity and habitats. They also cause soil erosion and flood risk, and impact railways, highways and buildings. The damage they cause can be particularly high in urban areas and developments where buildings are undermined, with root systems liable to affect underground structures, foundations and drainage systems, and possibly render a property unsaleable.


The annual cost of invasive non-native species (plants and wildlife) to the UK economy is estimated to be around £2bn, with Japanese Knotweed alone running up a yearly bill of over £200 million. [4]


According to the RICS, there are an estimated 1.45 million homes affected by Japanese knotweed in the UK [5] and mortgage lenders often take a very dim view of properties if this or any other type of invasive perennial weed is flagged up in a pre-purchase survey. Whilst there is a certain amount of misinformation that has been driven by the fears around what these weeds can do - the ability of Japanese Knotweed to ‘eat through concrete’ is unfounded! - appropriate remediation from expert professionals can ensure a favourable outcome for all parties involved.


Consequently, and in addition to the plethora of considerations to be taken into account when developing a new site for commercial or residential use, contractors have a duty to include invasive non-native species on the list. The contractor should commission a full site survey to determine the extent of the infestation, whether that be Japanese Knotweed or any other regulated species.


In-depth site surveys can be carried out using a variety of methods to identify the areas of contamination. Once these have been ascertained, a set of treatment, removal and containment recommendations is then drawn up.


Treatment of regulated plants normally involves spraying with glyphosate, with all affected areas being fenced off and compulsory foot washes implemented to ensure against any further spread. Once the weeds have been sprayed, the plants can be either physically removed to a controlled waste site, and/or if site conditions allow, buried in situ in a sealed cell for example under an area not intended for habitation such as a car park. Soft landscaping can be employed subsequently to cover any burial pits.


To prevent reinfestation, consideration must also be given to boundaries with vertical barriers sometimes being required if the roots have penetrated through to neighbouring land.


Jomas Associates are able to undertake full site surveys to identify invasive non-native species. We will then work with our remediation contractor to remove the regulated weed(s) in line with all statutory requirements ensuring the solution is cost-effective and minimises delays to the construction programme to protect the value of your land development.


In addition to invasive non-native species surveys, Jomas Associates undertake site investigations, land contamination risk assessments, geotechnical engineering surveys, flood risk assessments, and are award-winning environmental and engineering specialists, working on construction sites across the UK. We pride ourselves on offering pragmatic, highly qualified, competitively priced, value engineering with pace. We’d be happy to talk to you about any future project you have and how it could be conducted to save you both time and money.


[1] https://environment-analyst.com/uk/105616/uk-playing-catch-up-on-invasive-species

[2] https://www.nationalgeographic.co.uk/environment-and-conservation/2019/07/deadly-invaders-non-native-species-threatening-british

[3] http://www.nonnativespecies.org/index.cfm?sectionid=55

[4] https://geographical.co.uk/uk/uk/item/2682-the-hidden-costs-of-invasive-species

[5] https://www.rics.org/uk/news-insight/latest-news/press/press-releases/japanese-knotweed-doesnt-have-to-derail-home-sales-with-new-rics-guidance/