Invasive Species Week 2022

Invasive Species Week 2022

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16th to 22nd May hails Invasive Species Week 2022. Invasive Species Week is an annual national event to raise awareness of the impacts of invasive non-native species, the simple things that everyone can do to prevent their spread, and some of the fantastic work taking place across the UK, Ireland, Jersey, Guernsey, and Isle of Man to protect the environment and reduce their impacts.

Why not take part in this year’s Invasive Species week? You could host an event, find a Local Action Group, or look out for invasive plants while you’re out walking. Find out more about how you can take part.

What is an invasive non-native species (INNS)?

Invasive non-native species (INNS) are sometimes referred to as ‘invasive alien species’. These non-native species, such as Japanese knotweed and North American signal crayfish, can spread rapidly and become dominant in an area or ecosystem, causing adverse ecological, environmental and economic impacts. INNS can also affect our health.

It is important to remember that only a small number of non-native species become invasive, but these few can have serious negative impacts.

The impact of invasive species in the UK

Over 3,000 plants and animals have been introduced to the UK from all over the world by people. These are known as non-native species. Most are harmless, but around 10-15% become invasive non-native species (INNS) that spread and have a harmful impact.

INNS are one of the top five drivers of global biodiversity loss. Here in the UK, they threaten the survival of native wildlife, damage our natural ecosystems, cost the economy over £1.7 billion a year, and can even harm our health and interfere with activities we enjoy.

The United Nations Convention on Biological Diversity (CBD) identifies INNS as a major threat to biodiversity. Many non-native species do not threaten biodiversity, but INNS can spread disease (e.g. North American signal crayfish), modify ecosystems (e.g. Rhododendron ponticum), and drastically reduce populations of native species (e.g. American mink), or hybridise with native species (e.g. Ruddy duck).

Under the CBD, the UK has an international obligation to address the impacts of INNS. In 2008, the UK Government published the Invasive Non-native Species Framework Strategy for Great Britain.

30% of the UK’s Important Plant Areas have been found to contain invasive non-native species.

The impact of INNS on our woods

Our woods have been affected by invasive species in several ways. For example, the introduction of non-native deer species, Muntjac, for hunting has become a serious issue. Lack of natural predators means deer numbers can grow unchecked. The increased population feeds on tree saplings and hampers the process of natural regeneration. These deer are preventing the next generation of trees from developing.

Grey squirrels, introduced from America in the 1870s, strip the bark of trees, especially fresh growth. They have outcompeted native red squirrels. They also carry the squirrel pox disease which our red squirrels are particularly susceptible to. As a result, red squirrel populations have plummeted to the point where they can now only be seen in small areas of Great Britain.

The threat from Japanese knotweed

Many harmful INNS plants started as ornamental plants. However, in their new environment, they are free from native predators, pathogens, and competitors, allowing them to grow without competition. This is exactly the case for Japanese knotweed.

Japanese knotweed was introduced as an ornamental garden plant in the 19th Century. It’s now common in urban areas, particularly on wasteland, railways, roadsides, and riverbanks. But it affects our woods too. For example, it:

Even the smallest fragment, 0.5g, of rhizome (root) can propagate into a new plant, so it also spreads easily, making it challenging. In fact, Japanese knotweed is listed on the Wildlife & Countryside Act 1981 Section 14, Schedule 9, Part II, which prohibits its introduction into the wild. You could be fined up to £5,000 or imprisoned for up to 2 years if you allow contaminated soil or plant material from any waste you transfer to spread into the wild.

The "mad" invasive: Rhododendron

Rhododendron ponticum arrived in the UK during the 18th Century and was commonly used as a root stocking for grafting, but with neglect, the hybrids have become the common ponticums again.

It can spread to fill the space which is available to it, either remaining as a small shrub or, if light conditions and other resources allow, out-competing and displacing all other vegetation and local fauna. The cost of clearing R. ponticum from the Snowdonia National Park has been estimated at over £30 million.

The nectar and leaves of the Rhododendron contain poisons called grayanotoxins. They act as a natural defence from herbivore attack. The honey from the Rhododendron nectar is commonly referred to as “mad honey”. Consumption of the honey can result in grayanotoxin poisoning. Despite the risk of cardiac problems, grayanotoxin poisoning is rarely fatal in humans. In fact, in some regions of the world, the honey is consumed as a recreational drug and traditional medicine.

Carrier of pox: Grey squirrel

The grey squirrel is native to North America and was first released into the UK in the 19th century.

Grey squirrels outcompete the native red squirrel and are highly invasive due to their prolific breeding cycle. If food is available, female grey squirrels can have two litters of young per year. Eradication programmes for grey squirrels rarely work as neighbouring populations of grey squirrels will fill the habitat availability left by the eradicated squirrels.

Grey squirrels carry squirrel pox which can be carried and spread by grey squirrels and kills red squirrels, but the grey squirrel is unaffected.

Grey squirrels also impact woodlands by stripping bark off the trees, so they can feed on the soft inner layers. The trees can suffer severe damage, or even die, depending on the level of damage caused.

The impact of invasive species on the World

13% of all extinctions and specifically 40% of all animal extinctions since 1500 have been caused entirely by INNS. Aquatic invasions have cost the global economy US$345bn.

A 2017 study found that over 33% of all introductions in the past 200 years occurred after 1970 and the rate of introductions is showing no sign of slowing down. In fact, a 2020 study predicts the number of established alien species will increase by 36% between 2005 and 2050.

Many INNS can expand rapidly to higher latitudes and altitudes as the climate warms, out-pacing native species. INNS that are regularly introduced by humans but have so far failed to establish may succeed in doing so thanks to climate change, bringing new INNS to new shores.

INNS reduce the resilience of natural habitats, making them more vulnerable to the impacts of climate change. For example, some INNS grasses and trees can significantly alter fire regimes, especially in areas that are becoming warmer and drier. This increases the frequency and severity of wildfires and puts habitats, urban areas, and human life at risk. INNS can also impact agricultural systems by reducing crop and animal health.

What can you do?

There are simple things you can do to help prevent the spread of INNS.

Check Clean Dry


Check your equipment, boat, and clothing after leaving the water for mud, aquatic animals or plant material. Remove anything you find and leave it at the site.


Clean everything thoroughly as soon as you can, paying attention to areas that are damp or hard to access. Use hot water if possible.


Dry everything for as long as you can before using elsewhere as some invasive plants and animals can survive for over two weeks in damp conditions.

Find out about some of the INNS in our waterways.

Be Plant Wise

Know what you grow

Choose the right plants for your garden, pond, and water features.

Stop the spread

Keep your plants in your garden - don't plant them, or allow them to grow, in the wild.

Compost with care

Dispose of your unwanted plants, roots, weeds, seeds, and seed heads responsibly.

Be Plant Wise materials and resources are available from the GB Non-Native Species Secretariat’s website.

Get involved!

Find out how you can take part in 2022’s Invasive Species Week. Over 250 organisations took part in 2021.

Help to protect our environment and wildlife for future generations to enjoy by taking part in Invasive Species Week!

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