Wear Invasive Non-native Species (WINNS)

An exploration of invasive species across the Wear catchment

A volunteer bashing balsam in Hopper's Wood during the summer of 2022

Non-native Species are species that have been moved outside their native range by humans, either accidentally (e.g. via crops, footwear, vehicles etc.) or on purpose (e.g. ornamental plants, pest control etc.). Most of these species don't cause any problems for humans or native wildlife, but some have the potential to threaten biodiversity and damage structures. These damaging species are known as Invasive Non-native Species, or INNS for short. Globally, INNS are one of the biggest drivers of biodiversity loss and their impacts are only likely to get worse with climate change. It's hardly surprising, then, that the Wear catchment is badly affected by a variety of invasive species. Check out the interactive map below - can you name the 3 species that are most widespread?

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WINNS 23/24_2

The 3 main players

The 3 key invasive species in the Wear catchment are Himalayan Balsam (Impatiens glandulifera) with its pink, nectar-rich, trumpet shaped flowers; Japanese Knotweed (Reynoutria japonica), which forms dense bamboo-like stands and has leaves arranged in a characteristic zigzag pattern, and Giant Hogweed (Heracleum mantegazzianum) with its huge umbrella-shaped flower heads that can reach heights of 5m.

From left to right: 1. Himalayan Balsam flowers, 2. Himalayan Balsam seed pods, 3. Japanese Knotweed leaves, 4. Winter stand of Japanese Knotweed, 5. Man next to fully-grown Giant Hogweed, 6. Giant Hogweed leaves

Himalayan Balsam was introduced to the UK by Victorian plant enthusiasts and was prized for its attractive, nectar rich, pink flowers. Unfortunately, though, it can cause huge problems for our native wildlife and waterways. It spreads extremely quickly thanks to its spring-loaded seed pods, which are able to throw seeds up to 7m away. These regularly land in moving water, spreading the seeds downstream. Once Himalayan Balsam has a foothold, it soon forms dense stands that quickly outcompete surrounding plants. The flowers have large nectar reserves, which are a huge reward for pollinators, consequently lowing the chances of pollination for our native flowers. On top of this, Himalayan Balsam is an annual, meaning it dies back each winter, leaving bare, exposed ground, which increases the risk of erosion and has a negative impact on water quality.

Japanese Knotweed was also introduced to the UK in the 1800s and was once prized within horticultural circles. It is now considered one of the top 10 most damaging invasive plants globally. It spreads along our watercourses via rhizomes and outcompetes native flora. Additionally, it is economically damaging due to its ability to grow through man-made structures such as roads and buildings.

Giant Hogweed, again introduced during the 19th century as an ornamental plant, is an extremely problematic plant. Not only does its vast size allow it to bully native plants, but it also poses severe risk to human health due to its phototoxic sap. If it comes into contact with bare skin, the sap reacts with sunlight and causes burns and blistering that can remain sensitive for several years. Consequently, Giant Hogweed must only be handled by trained professionals and volunteers.

Use the interactive map below to explore how, and where, invasive species are impacting our catchment, and what we are doing to try to control their spread.

An interactive tour of WINNS

The source of our Giant Hogweed problem

Surveys carried out by Wear Rivers Trust staff and volunteers have traced the source of Giant Hogweed to Coalford Beck, just north of Pittington Village. Huge stands are present along the Pittington and Coalford Becks, and down onto Old Durham Beck, which joins the main river Wear in the Maiden Castle district of Durham City.

Japanese Knotweed at the top of the catchment

Unlike Giant Hogweed, Japanese Knotweed is widespread across the whole catchment - we have found the plant high up in St. Johns Chapel, Weardale. Japanese Knotweed is extremely hard to eradicate, as it can grow from tiny root fragments - 0.7g is enough for it to bounce back! Parts of the roots are often spread downstream in flood events, meaning it's very common to find the plant along our waterways.

Japanese Knotweed relatives and hybrids

In the UK Japanese Knotweed almost always spreads vegetatively - via root fragments. This is because we only have female Japanese Knotweed plants, meaning they can't undergo pollination and produce viable seed.

Balsam Bashing in Hopper's Wood

Japanese Knotweed and Giant Hogweed need to be managed by professionals and volunteers that are trained in the safe use and application of pesticides. Thankfully, Himalayan Balsam can be managed by anyone. This provides us with great opportunities to get communities together to make a positive impact on their local environment. Here at Wear Rivers Trust, we regularly put on 'Balsam Bashes' throughout late spring and early summer. Keep an eye on our get involved page to find an event near you.

Getting to grips with Himalayan Balsam in Weardale

Like Japanese Knotweed, Himalayan Balsam can also be found at the top of the Wear Catchment, throughout Weardale.

The source of our Giant Hogweed problem

Surveys carried out by Wear Rivers Trust staff and volunteers have traced the source of Giant Hogweed to Coalford Beck, just north of Pittington Village. Huge stands are present along the Pittington and Coalford Becks, and down onto Old Durham Beck, which joins the main river Wear in the Maiden Castle district of Durham City.

As Giant Hogweed is only present in a relatively small section of the Wear catchment, we are hopeful that we'll be able to get to grips with the issue in the coming years. We have already seen positive results from our management regime, and are well on our way to cutting the plant off at its source.

Citizen science schemes and biological recording centres, such as  ERIC North East  help us to keep up-to-date with sightings. This means we can act fast if plants are seen higher up the catchment than Pittington.

Japanese Knotweed at the top of the catchment

Unlike Giant Hogweed, Japanese Knotweed is widespread across the whole catchment - we have found the plant high up in St. Johns Chapel, Weardale. Japanese Knotweed is extremely hard to eradicate, as it can grow from tiny root fragments - 0.7g is enough for it to bounce back! Parts of the roots are often spread downstream in flood events, meaning it's very common to find the plant along our waterways.

When managing invasive species, it makes strategic sense to start from the top of the catchment, and work your way down. Plants like Japanese Knotweed take years of effort to tackle, meaning St. Johns Chapel is an important site for us.

Japanese Knotweed relatives and hybrids

In the UK Japanese Knotweed almost always spreads vegetatively - via root fragments. This is because we only have female Japanese Knotweed plants, meaning they can't undergo pollination and produce viable seed.

Unfortunately, a closely related cousin - Giant Japanese Knotweed (Reynoutria sachalinensis) - does have both male and female plants present in the UK, and they can hybridise with R. japonica to create Reynoutria japonica x bohemica or 'Hybrid Knotweed'. These hybrid plants are able to produce viable seed, and should be monitored carefully.

Luckily, Giant Japanese Knotweed is far less widespread than normal Japanese Knotweed. In the Wear catchment, one of the few sites is located on the Sands, just north of Durham City Centre. This stand is being carefully monitored, and management plans are in place.

Balsam Bashing in Hopper's Wood

Japanese Knotweed and Giant Hogweed need to be managed by professionals and volunteers that are trained in the safe use and application of pesticides. Thankfully, Himalayan Balsam can be managed by anyone. This provides us with great opportunities to get communities together to make a positive impact on their local environment. Here at Wear Rivers Trust, we regularly put on 'Balsam Bashes' throughout late spring and early summer. Keep an eye on our  get involved page  to find an event near you.

Getting to grips with Himalayan Balsam in Weardale

Like Japanese Knotweed, Himalayan Balsam can also be found at the top of the Wear Catchment, throughout Weardale.

Weardale is a fascinating and beautiful area. The region's rich culture and mining past is written within the landscape, and small burns and tributaries hold wonderful wildlife.

One such tributary, Rookhope Burn, has unfortunately got a Balsam problem. The invasive plant is posing risks to local biodiversity and water quality. It also threatens sites of high value downstream.

Thankfully though, with monumental volunteer efforts, and the help of our friend's at Northumbrian Water, we are getting to grips with the problem. We are on track to prevent any seeds from setting on Rookhope Burn in 2023, allowing us to focus our efforts further downstream in the future.

A volunteer bashing balsam in Hopper's Wood during the summer of 2022