Beavers – slowing the flow in Cropton forest
Cath Bashforth, ecologist at Forestry England, gives an insight into the Yorkshire enclosed beaver release trial.
What work are you doing?
In April 2019, 2 adult beavers from Scotland were released into an enclosure in Cropton forest as part of a 5 year trial. The enclosure is securely fenced and is just over 10ha in size, it is situated in the river Seven catchment.
How does this trial relate to improving climate resilience?
The stream rises and falls very rapidly and was part of the ‘slowing the flow’ project which started in 2007 to look at the impact of man-made woody dams reducing the peak during storm events. This earlier project had been established in an effort to reduce flood damage in Pickering and Sinnington downstream.
What are the aims of the trial?
The main aim of the trial is to monitor the way that the beavers interact with the man-made woody structures in the beck - to see if they will adopt and maintain them on our behalf. There is one large timber bund in the site and 3 smaller man-made dams.
Other aims of the project include assessing the additional amount of water retention and how the water moves through the site, the beaver’s impact on biodiversity within the enclosure and also their effect on rhododendron. It is also hoped further into the project that the potential for ecotourism can be investigated.
How do you monitor the impact of the beavers?
Exeter University have been working on the hydrological monitoring of the watercourses and also undertaking aerial drone imagery. Leeds University have been involved with laser scanning several areas and Teesside University have undertaken aquatic vegetation surveys.
Over 40 volunteers have been involved, surveying plants, bats, small mammals, otter, amphibians and reptiles, mosses and liverworts, butterflies, dragonflies, diptera and fungi. The volunteers were invaluable in pulling together a fantastic baseline of information of site biodiversity and this will be monitored throughout the 5 years of the trial.
We also monitor the beavers closely with 12 trail cameras throughout the enclosure to capture footage of behaviours and monitor their health and wellbeing.
What water engineering have the beavers done so far?
The 2 beavers have quickly made the site home. They set to work straight away plugging the leaks in the top pond and the water levels have now increased by over a metre in both ponds. The beavers constructed an amazing canal to connect the bottom pond to the top pond. Beavers move much more easily in water and feel more comfortable, so this was to aid their travel between the ponds.
In addition, the beavers have built a large dam in the river which is now over 6ft tall. This has significantly raised water levels upstream to enable them to burrow into the banks and create an underwater entrance into their lodge, which they have constructed on the river bank. They have since extended this dam across the floodplain, connecting the pond and the river, and built up the bottom pond edge by 30cm along its whole 60m length to hold back even more water, significantly changing the way the water moves through the site.
So far the beavers have not worked on the man-made structures – but it is early days yet.
Have the beavers slowed the water flow?
Now, water is forced out across the floodplain in periods of heavy rain instead of rushing down the river channel, resulting in a multi-braided watercourse which effectively slows the flow.
Early results from Exeter University’s monitoring show that the beavers’ structures do indeed seem to be helping to reduce the peak of the water flow through the site, although it is still too early in the project to be conclusive.
How have beavers impacted on biodiversity? Their work has resulted in a record amount of amphibians recorded at the site. Before the beavers were released just 6 clumps of spawn were recorded, this year the amount of spawn was uncountable. Because of the number of frogs and toads over 12 herons have been regularly seen fishing around the pond and both otters and tawny owls have been caught on camera feasting on the amphibians. Teal and Mandarin have been spotted on the site for the first time too because of the increased water levels.
The beavers have also coppiced many of the trees overhanging the pond - opening it up to a lot more light. This has seen foxgloves and other vegetation appearing along the pond banks which were not growing here before due to the amount of shade. The willow trees are already coppicing back up with abundant shoots – a future resource for the beavers. Interestingly many of the stems were ‘pleached’ (left attached) and fell into the water meaning that the shoots that grow will be much more accessible to the beavers going forward – was this accident or planning?
Male beaver photo credit: © Forestry England, Sam Oakes.