Posted on May 16, 2022

Developers, watch out for these invasive species

Why do invasive plant species need controlling?

Not only can invasive plants be detrimental to our native flora, if unidentified or not properly controlled, they can cause costly delays to a project and even lead to prosecution.

Under Schedule 9 of the Wildlife and Countryside Act, 1981 (as amended), developers are legally required to prevent invasive non-native plants on their land from spreading into the wild. This can include moving contaminated soil or plant cuttings. Developers are also obligated to prevent invasive weeds on their land from spreading onto a neighbour’s property.

Here are our top five invasive plant culprits commonly found around development sites:

Himalayan balsam

Himalayan balsam Invasive Species Week

Himalayan balsam (Impatiens glandulifera) is an easily recognisable and rather common species of riverbanks and damp places. Its explosive seed heads can spread the seeds widely, particularly via water. It often forms dense stands to the exclusion of native plants.

During the summer, the lush growth can impede water flow and lead to flooding. When it dies back in the winter, it can leave bare banks exposed to erosion. Care needs to be taken not to spread the seeds further during control, particularly within contaminated soil.

Giant hogweed

Giant hogweed Invasive Species Week

A frequent and unmistakable invader, particularly along riverbanks, giant hogweed’s (Heracleum mantegazzianum) large size (up to five meters tall), rapid growth and abundant seed production can cause it to dominate native vegetation and block access to riverbanks.

This leads to soil erosion and increased flood risk, and poses a risk to human health as it can cause serious skin blisters. It can be troublesome to control, due to rapid re-growth from the seed source within the ground.

New Zealand pigmyweed

New Zealand pigmyweed Invasive Species Week

If your site has still or slow flowing water bodies, there is a risk you have New Zealand pigmyweed (Crassula helmsii) as it is spreading fast throughout the UK. It can be troublesome, forming dense mats that can impede drainage and cause flooding, as well as displacing native plants and reducing the amenity value of the waterbody.

It is also very easy to spread into the wild and thus contravene legislation, as it can reproduce from tiny fragments of stem. Appropriate handling and disposal by an experienced contractor are essential.

Japanese knotweed

Japanese knotweed invasive species week

Japanese knotweed (Reynoutria japonica), is often encountered on development sites, as it can tolerate a wide range of disturbed conditions, such as urban areas, schools, watercourses and waste ground. Its strong shoots can damage hardstanding and it can be difficult to eradicate. It does not produce seed in the UK but, like New Zealand pigmyweed, Japanese knotweed can regrow from small fragments of the plant.

Cotoneaster species

contoneaster invasive species week

A large group of small trees and shrubs introduced from East Asia, spread readily by birds eating the berries and can come to dominate rough or waste ground. Five cotoneaster species are listed under Schedule 9 of the Wildlife and Countryside Act and they can form an extensive root system, proving difficult to eradicate.

What are the costs to your business?

Invasive non-native species cost the British economy approximately £1.7 billion per year (Williams et al., 2010). The cost for your business can be minimised by seeking expert advice at the earliest stage in your project.

If detailed expert surveys are not conducted or inexperienced personnel are used for clearance, invasive species can either be overlooked or mishandled. This can lead to costly delays during construction.

How we can help

At Thomson environmental consultants, we can help you through the entire process, so that your project can continue to run smoothly. Invasive species surveys undertaken by trained botanists can often be incorporated into other essential ecology surveys. We can help you develop an invasive species management strategy, as well as remediation and treatment services, to ensure that you comply with relevant legislation, while providing efficient and reliable removal and disposal in line with best practice.

To discuss any concerns over invasive non-native species, or to obtain a quote, get in touch today.

Tel: 01483 466 000
Email: [email protected]


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      Knowledge Hub Developers, watch out for these invasive species