What and Where

What is a non-native species?

Non-native species are any species either terrestrial, freshwater or marine that did not naturally occur within the United Kingdom before people first arrived after the last ice age.

What is an invasive non-native species?

An invasive non-native species is any non-native species that causes, or is thought may cause, serious negative impact on our native species, our health or our economy. The distinction between non-native and invasive is important as there are many non-native species that are not invasive and pose no threat. This is particularly true in London where we have a range of naturalised non-natives that form important roles in our urban ecosystems. Any species that is native to one country, including Great Britain, can become invasive if introduced to an area outside its natural range. A list of species of concern can be found on the ‘species of concern’ page.

So why do species become invasive?

Plants, animals, fungi and micro-organisms have become increasingly mobile throughout the world. This has brought species into ecosystems that have developed without them, and without the conditions that limit their growth in their natural system (nutrients, moisture, pests, diseases, etc.). This allows some species to grow and reproduce unchecked. The ecosystem is unable to cope with this new species and is thrown off balance. This population increase can then result in damage to the ecosystem, our health or our economy and more often a combination of all of these. This is when invasive non-native species become a problem and management is needed.

Why is London in a unique position?

London differs to other areas in the UK most noticeably with regard to climate, habitat and overall land use. These factors help to define the range, density and behaviour of invasive non-native species and can lead to invasive non-native species behaving differently in London to how they behave in the rest of the UK.


London is subject to the ‘urban heat island affect’ where heat created from items such as air conditioners, cars etc. is stored in building materials and hard surfaces such as pavements, and redistributed back into the environment. This only occurs in highly urbanised areas and makes the average temperature within London higher than would normally be expected. Climate defines many aspects of species behaviour and is related to their ability to survive in a new location. Low temperatures can be a limiting factor for many invasive species within the UK. We may be able to use London to predict possible trends of invasive non-native species establishment, distribution, density and behaviour for other areas in Great Britain as the climate warms.


London is a highly urbanised world city with a long history. It is a major international port for both travel and trade. Through these connections to the world we intentionally and unintentionally transport species from and into Greater London. We intentionally transport species for agriculture, horticulture and the pet trade. Unintentionally, we transport stow-a-way species via shoes, equipment and in vehicles. Urban areas also have a variety of available ecological niches and an abundance of critical resources i.e. food, water and shelter. This means that any arriving species will have a variety of different habitats available, increasing the chance of their finding one that is suitable. This can be problematic for surrounding rural areas as species can become established in London where they do not cause damage then move to rural areas where they can. Management of these species can be over looked in urban centres as the need for direct  management may not be understood until a source population is well established and by then it can be too late.


The people that live, work and travel in a city determine how invasive non-native species are perceived and how action needs to be communicated, carried out and explained. London has a highly cosmopolitan population, something which comes with a range of ideas about and relationships with nature. People’s connection to the environment varies widely. There is a need for us as land owners, managers or researchers to find ways to communicate with the wider community as they can assist us in influencing government priorities and guiding practical action, whilst significantly contributing to work directly through volunteering.

Proximity to existing populations:

A large amount of movement of human populations occurs between Europe and the UK. A large portion of this goes through London. This movement is a major pathway for the potential spread of new invasive non-native species into the Greater London area.

All these factors combine to provide a unique set of conditions. London provides both the means for invasive non-native species to enter the UK, and provides a range of habitat conditions able to sustain new species and populations.

There is a need for London to be at the forefront of invasive species management so that any potential new incursions can be prevented or managed quickly and effectively.

Where are they?

LISI works with a range of partners to collect invasive non-native species data. More information can be found in the ‘Surveying and Reporting INNS’ section of this website.