Tamar Invasive Plants Project

The Tamar Valley AONB delivers the Tamar Invasive Plants project, on behalf of a partnership of four organisations (Tamar Valley AONB, Environment Agency, Natural England and Cornwall Council – known collectively as the Tamar Invasives Group).

The project continues treatment to control Giant Hogweed on an annual basis. Numbers of plants have shown a progressive decrease in the survey area in recent years. However, the 2021 season showed a slight increase which demonstrates the need for constant vigilance to prevent the spread of this invasive species.

Giant Hogweed Eradication Project survey and control update

The full survey and control of Giant Hogweed took place in 2021, with the support of all landowners currently involved in the project, including the owners of a property where permission was withheld in 2020 due to concerns about the transmission of Covid-19 during the first pandemic lockdown in England.

We are awaiting the final survey data from our control contractor, but early reporting shows that the total number of Giant Hogweed plants has increased since last year, with a current reported rise from 61 plants in 2020 to 277 in the main project area in 2021. Adding to this the Giant Hogweed found in non-riparian sites surveyed last year, shows an increase in the total number of Giant Hogweed surveyed and controlled by our contractors in the project area from 96 in 2020 to 300 in 2021.

It should be noted that the area with the greatest increase was the estuarine Calstock to Gunnislake section, with an additional 216 plants located this year, up from 44 in 2020. We are unlikely to see the upstream spread of this local population into the non-estuarine sections the project area. In addition, most of this increase is due to a cluster of newly geminated plants found at the site where the consent to survey was withdrawn last year, and which is a known hot spot for Giant Hogweed in the valley. The landowners of the site later reported removing approximately 12 plants from property but, due to the difficulty in physically moving around this site to carry out a complete survey, the likelihood that a flowering plant went undetected is a very real possibility.

In other sections of the main project area, we have seen smaller changes in plant numbers, including reported single figures in 3 of the 5 project area sections, although we are waiting for the final reporting of 2021 survey data. With regards the additional non-riparian sites, combined numbers are down from 35 plants in 2020 to 23 plants.

Landowner consent is an ongoing issue with a collaborative programme of this scale and it is important to engage as many landowners as possible to minimise the opportunities for the plant to spread. There are some areas in the project catchment area where consent is not granted or the landowner carries out their own survey and control. We take every opportunity to engage with these landowners when the opportunity arises so that we can continue to monitor the situation in these areas.

The importance of engaging with the general public to encourage the reporting of Giant Hogweed sightings is clear and this year the AONB office was notified about two separate sightings, including an unexpected cluster of 5 plants in an atypical location about 1km beyond the project area, and the report of 2 isolated flowering plants in the estuary by a passing canoeist. Renewed efforts to inform and engage the general public will be made before the 2022 season.

As part of this effort, a public engagement event, expected to be held face-to-face in the spring of 2022, will include a presentation on the results of an independent review of the Giant Hogweed Eradication project currently taking place and funded through the Water Environment Grant (WEG) programme. The event will also offer an opportunity to consider the status of other Non Native Invasive Species (NNIS) in the Tamar Valley catchment.

The Tamar Valley AONB and our partners in the Tamar Invasives Group, are grateful to have been awarded an additional £10,200 funding through the Water Environment Grant (WEG) earlier this year, covering the cost of the 2021 survey and control work. In addition, South West Water generously donated an additional £4895 in 2021, ring-fenced for future invasives work in the Tamar Valley.

Encouraging better water primrose reporting – August 2021

It’s this time of year that non-native invasive water primrose (Ludwigia grandiflora) is in full bloom, which makes identification much easier. NNSS has provided a landing page on their website for potential new records.

Please can you look out for water primrose and report any sightings asap. The Environment Agency have recorded 44 sites, 16 of which have been eradicated. This is a tough plant to kill, so they want to manage sites before water primrose can get too established.

Images are available on the GB NNSS gallery with lots of other information on the species page, too.

Contact us

For more information about the project please contact Valerie Darwall on 01822 835030 or email vdarwall@tamarvalley.org.uk


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