Efforts to control INNS are demonstrated in UK law, for example The Wildlife and Countryside Act 1981, which aims to prevent and minimise their introduction and spread. A list of INNS species can be found in the Act which includes 30 birds and 11 amphibian and reptile species, as well as 10 mammal species, including the American mink (Neovison vison), responsible for a dramatic decrease in water vole populations across the UK, and grey squirrel (Sciurus carolinensis), which is responsible for the decline in our native red squirrel numbers.

The Act also includes 36 plant species, each recognised as being particularly harmful to our native habitats and species. Japanese Knotweed (Reynoutria japonica) is perhaps the most famous of these, known for its particularly aggressive and persistent growth. Native to Japan, China and Korea, the plant was introduced in the mid-1800s for use in gardens and rail embankments and by the 1970s it had spread across Britain. The plant is a tall perennial, surviving year upon year, and can rapidly grow outwards from underground stems named rhizomes, forming large, dense patches. The main problem with Japanese Knotweed is within the built environment, as the roots of the plant can be very vigorous, being known to grow through tarmac, drains, and foundations. It spreads through tiny fragments of their rhizomes separating from the parent plant, which then establish new plants. It can quickly spread through an area unintentionally via the movement of soil and other building materials, and once in a location, can be very difficult and costly to remove.

Himalayan Balsam (Impatiens glandulifera) is another harmful plant species, introduced in the 1830s to the UK from the Himalayas for its ornamental properties. It is an annual, completing its life cycle from germination to death within a year. It spreads via seeds, which are particularly well adapted to dispersal as the seedpods burst, launching seeds several metres away from the parent plant. Each plant can produce up to 800 seeds, which are able to float and so can travel significant distances via waterways. Once established, the plants form dense colonies that quickly grow to over one metre tall, casting shade upon the vegetation below and reducing its ability to survive. The roots of the plant are shallow in comparison to our native vegetation and therefore when it dies each winter it can leave the banks bare of vegetation, without stabilising root systems. This can increase erosion into our watercourses as well as reducing the diversity of habitats, which in turn affects native species.

Rhododendron (Rhododendron ponticum) is a large shrub with large pink flowers which was originally introduced for garden use in the 1700s from the Iberian Peninsula. It is now established over much of the UK and has become a threat to native woodland. It produces small seeds that can be dispersed up to 100 m by wind and even further by water, remaining viable in the soil for many years. It can grow prolifically in woodland and once established few native plants survive, as its dense foliage casts shade upon the ground. Only trees which grow above the level of the rhododendron canopy can persist; however, when these trees die, they are generally not replaced as their seedlings cannot grow under the lightless canopy.

Building development projects can be a leading driver of the spread of terrestrial INNS, especially plants. The huge number of different sites connected by the shared use of equipment and personnel between these means that the spread of INNS can be easily facilitated. Due to the legislation surrounding INNS, landowners and land managers have a responsibility to prevent the spread of INNS from their site. Demonstrating that development projects have exercised due-diligence with regard to INNS is advisable, and best-practice can be achieved through correctly identifying INNS at a site, obtaining sound mitigation advice, following good management practices, and adopting a precautionary approach.

Consideration of INNS at an early stage is advised for developments of all sizes. Early detection of INNS within a site can lead to significant cost savings as it facilitates more informed and efficient decision making with regard to site selection, design and implementation. Eradication of INNS from site can become costly once they are established and so the knowledge of their presence can be very beneficial when considering land purchase. Management of INNS on a site can take many forms depending on the species present and the scale of the infestation, including avoidance, mitigation using biosecurity protocols, and eradication.

APEM’s skilled ecologists are experts in the identification, mitigation, control and eradication of INNS in both the aquatic and terrestrial environment. We regularly prepare risk management strategies, design mitigation measures and develop biosecurity protocols. We also manage specialist contractors to eradicate INNS infestations from a site.

To find out more about the INNS services APEM offer please visit our webpage.

Further information on INNS can be found at the following websites:





[1] F. Williams, Fl. Eschen, A. Harris, D. Dieddour, C. Pratt, R. S. Shaw, S. Varia, J. Lamontagne-Godwin, S.E. Thomas, S. T. Murphy (2010). The Economic Cost of Invasive NonNative Species to the British Economy. CABI, Wallingford