Biosecurity and Non-Native Terrestrial Plants

Biosecurity measures are essential on all construction sites even if they are not known to be present on site, some may ask why? One reason may be that invasive plants may completely die back and disappear in winter or become hard to identify, therefore they may have been missed in surveys; or in cases where rapid growth is seen, they may have entered the site and spread in just the last growing season. Another reason is that biosecurity measures also aim to stop the introduction of species onto a site. While some invasive non-native species (INNS) spread by seeds, many spread by tiny vegetative fragments. Smalls seeds and vegetative fragments can easily catch a ride on plant, equipment or in the treads of shoes and tyres. Once on site they can be easily spread across the site, potentially even only being discovered post construction when new growth is discovered, leaving the contractor liable for potentially costly remediation. If discovered during works, a fast response for containment and management can be vital to minimise spread, delays and costs spiralling.

Furthermore, it is an offence if activities cause the spread into the wild of species listed under Schedule 9 of the Wildlife and Countryside Act 1981, or of species to a ‘location outside its native range’ under Wildlife and Natural Environment (Scotland) Act 2012). In this article we will explore the key terrestrial invasive flora to be aware of and which are listed under Schedule 9 (S9).   

Himalayan Balsam (S9) is one of the most widespread invasive plants in the UK, it spreads incredibly easily due to its explosive seed heads. Often establishing along waterways, they outcompete other plants in the summer yet die off in the winter, destabilising banks leading to erosion and increased flooding risk. These annual plants can grow to 3 metres high and can disperse seeds 3-5 metres away, with seeds remaining viable for 2 years. If you’re working anywhere near these plants during or after seeding (June onwards), make sure a buffer of a minimum 5m is maintained at all times. If access in closer proximity is required, then shoes should be cleaned and all earth and seeds removed from soles of boots and treads of tyres when leaving the area. 

Japanese knotweed (S9) is one of the most difficult plants to kill, simply cutting the plant back is not only ineffective, it severely risks spreading the plant and increasing the problem. To manage the plant, it is must be sprayed at a specific time of year or in some cases each individual stem must be injected; in more extreme cases where a quick turnaround is required or spraying is not suitable, the plants and the earth beneath are excavated. Unlike Himalayan Balsam which spreads by seeds, Japanese knotweed spreads through rhizome and stem regeneration, and it only takes a 0.7g piece of rhizome to grow into a new plant! Therefore, it is vital that all stands are identified before groundworks commence – this is sometimes a requirement in planning conditions. Current guidelines state rhizomes can spread up to 7m away from the centre of the plant, and as such, a significant exclusion zone is often needed. Not only can it spread easily, but it can grow through cracks and gaps or in extreme cases hard surfaces such as thin tarmac, posing a significant risk to construction projects if allowed to spread across a site!  

Giant hogweed (S9) looks similar to native cow parsley yet grows up to 5m tall. It reproduces by seed which are produced prolifically. In hot summer months it can spread rapidly, especially along riverbanks. Though hard to miss due to its size, its size is not what poses the greatest danger, the sap from the plant is “phototoxic” – this means that it can burn and blister the skin in the presence of sunlight. Any removals should be done with appropriate PPE to ensure the sap does not make contact with the skin!  

Rhododendron (S9) can cover vast areas so if clearance is required, mechanical cutting and chemical treatment will often be needed to eradicate the species from site. An appropriate contractor and plan to deal with the waste should be in place for successful eradication and spread control.  

Buddleia (non S9) are a common waste ground INNS. Seeds blown into cracks germinate and the young plants root into the masonry which can cause structural damage to brickwork. Seeds are spread easily and the damage it can cause may be greater than those on Schedule 9, so despite there not being any legislative controls in place, it is worth not overlooking these if present on site.

Ensuring pre-construction surveys are undertaken is vital when any engineering or construction works are planned, especially in areas where invasives are known to be in the wider area or on waste ground. Biosecurity and invasive management plans should then be implemented to reduce the risk of spread or introduction of INNS. It is always worth remembering, if the construction activities facilitate the spread to the wild or to a ‘location outside its native range’ (Scotland), it would constitute an offence under Schedule 9 of the Wildlife and Countryside Act 1981 (in England and Wales) or Section 14 of the Wildlife and Natural Environment (Scotland) Act 2012). As a minimum, a ‘clean, check, dry’ method should be implemented on all sites.

Naturally complaint can undertake invasive species surveys and advise on how to manage them on your site, the earliest involvement of an environmental professional can often help to reduce any delays and costs due to INNS.