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15 May 2023 < Back

Invasive species in the built environment

Welcome to what is the start of ‘Invasive Species Week 2023’. As we raise awareness and draw attention to the impacts of invasive non-native species, we begin by looking at what an invasive species is and why they are an increasing concern within the built environment, not only in the UK, but globally impacting us financially, ecologically and mentally.

What is a Non-Native Invasive Species Plant? 

Invasive plant species are characteristically defined as non-native or exotic plants whose introduction and spread pose a significant impact on the environment, economy, and/or human health. These species can be introduced deliberately, like Japanese knotweed which was first introduced into the UK during the 1850s as a decorative, ornamental plant, with very little understanding of how the plant actually spreads. Whilst we know hindsight is a wonderful thing, the introduction of this plant costs the UK an estimated £165 million per year and has impacted the property market both in terms of property value and financial institutions reluctant to lend.

However, not all non-native plants introduced into the UK are a problem. Rapeseed was first recorded in the UK in the 14th century, but originates from India. The UK now produces roughly 1.5-2 million metric tons per year, which is worth £595 million to the UK economy, thus demonstrating that not every non-native plant automatically becomes a problem. 

The distinct difference between invasive non-native and just non-native plants, is their capability to spread from their initial introduction environment, and their ability to disrupt native plant species which can impact the sensitively balanced equilibrium within the environment. 

Finding the reason behind the invasive spread

Urbanisation and the built environment have created ideal conditions for invasive plant species to thrive. These conditions range from changes in soil quality to an increase in the number of abandoned urban landscapes which can harbour non-native plant species.

Quite often we find Buddleia emerging from brickwork several stores from ground level, where maintenance options are very limited. Himalayan Balsam or Giant Hogweed emerging throughout whole development sites where the land has been levelled, spreads the seeds from the plant to each of the four corners of the boundary. Or, Japanese knotweed located along the roadside through illegal transportation and fly tipping, where it gets left to spread even further into the natural environment. Not only do we introduce these native plants, but we actively encourage their spread…yet we wonder why these plants can often escape from their intended environment so easily.

Impacts of the spread

Professionals in the sector and those who have had the problem of dealing with invasive plants (whether on site or residential) will be aware that the impact is much greater than simply its capability of rapidly spreading.

Many invasive plants can have a significant impact on buildings and infrastructure such as roads and pathways. Most notable is Japanese knotweed. This pIant has the capability of exploiting tarmac or hard landscape features, causing damage to the immediate area and has caused a property blight incomparable to any around the globe.

These plants tend to create a monodominant society, meaning that very few have the capability or resources to survive within the area, reducing overall biodiversity. Plants like Bamboo create these monodominant societies, shading out everything at lower levels with their tall culms and provide very little in terms of biodiversity as they rarely produce a flower with pollen. Not only do they provide poor biodiversity opportunities, but they have the potential to expose pre-existing damage within built structures or paving as they force their way through tiny crevices. Their expansive growth capabilities can inevitably lead to further problems, from lifting paving slabs, to major wall damage and even finding entry within the internal property walls.

Health impacts with certain invasive species

The impact on human health can be very harmful even by simply touching some plants. For example, Giant Hogweed produces a toxic sap which causes phototoxicity, resulting in the affected area becoming extremely sensitive to UV light, creating blisters when exposed. 

Mental health must also not be forgotten. The worry which surrounds the taboo topic of Japanese knotweed when selling a property can pressure vendors into being deceitful when completing the TA6 form, or it may produce sleepless nights over the fear of their garden being overtaking by this 'triffid like plant'.

An opportunity for all of us to learn…

As we mentioned at the start, Invasive Species Week is about creating awareness around the impacts of invasive non-native species…but it is also about drawing attention to what you can do, whether you are a homeowner or a professional curious to learn more. 

Throughout the week we will highlight plants which could present a problem and the control options available for these plants - whether that is putting in steps to prevent them escaping from their intended environment, considering planting other native plants in their place or the importance of using accredited and professional contractors if things become out of control. 

As supporters of this annual event, we will be releasing blogs, news bites and videos which we hope will be helpful and insightful to all. BUT we are not the only place to get supporting information. If you are interested in the upcoming events for Invasive Species Week, then make sure you visit our unique webpage or the Non Native Species Secretariat events page, to see what is happening and what you can learn.

If you have any concerns…there are specialists you can talk to

As always though, if you do have any concerns regarding invasive weeds, then there are professionals who can help you. PCA's specialist invasive weed members will be happy to offer advice and guidance over the phone and, if you have pictures, will be happy to look at those before confirming if you need to book a survey. To find a registered PCA specialist near you, simply use the search tool below.

If you want to find someone to talk do, then click on the button below to run a local search…

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