Thompson Common pingos are some of the most biodiverse in Europe and support many scarce species, some that are found nowhere else in the UK. Unfortunately, some of the ponds were threatened by a non-native pond weed, Crassula helmsii, aka Australian Swamp Stonecrop. Crassula can form a dense mat across a pond’s surface that can prevent many other plants from growing, as well as removing food plants for many organisms and lowering oxygen levels. Left unchecked, the invasive plant would have spread into many of the ponds and wetland areas. 

Funded for the first two years by Anglian Water Invasive Species Fund and the past two years by Natural England’s Species Recovery Programme Capital Grants Scheme, the project aimed to find and remove all the Crassula NWT Thompson Common and eradicate it or at least reduce it to a level where it could not spread or impact biodiversity.   

NWT’s Crassula Officer, Julia Mumford-Smith, led the ambitious project. ‘Crassula helmsii is notoriously difficult to eradicate,’ she says. ‘Some ponds had large amounts of the plant which were easy to see but we suspected it had spread to other ponds in small amounts.  We wanted to find these and eradicate them before they got established and became extremely difficult to manage. With the help of volunteers, we searched over 1,276,369 square metres [equivalent to 187 football pitches] looking for a plant that can be 1cm tall, hiding amongst lush sedges and vegetation.’  

‘It is fantastic to see the diversity of plants and animals return to the areas that were infested by thick mats of Crassula,’ continues Julia. ‘Those areas are now a garden of water violet, tubular water dropwort, bladderwort and rare stoneworts with scarce liverworts floating past, stirred by the movements of water vole, water shrew, great crested newt, huge water beetles and Britain’s rarest frog. 

‘I would like to thank the 43 volunteers who gave their time to this project and worked relentlessly throughout the year including through icy winter weather and scorching summer heat to protect the fantastic wildlife of one of Norfolk’s most special places.’ 

Eradicating Crassula at NWT Thompson Common will also reduce the risk of the species spreading into the newly created ponds on land surrounding the nature reserve.