When you’re walking through a woodland and see an older tree with signs of decay, snapped branches with bits of dead wood hanging, cavities and hollows, this may well be a veteran tree. These veteran trees are important biodiversity hotspots, all their features providing something for wildlife within the woodlands. Hollows and cavities are great spaces for nesting birds. Slots created by snapped branches become homes for bats and insects. Deadwood is a perfect habitat for invertebrates.
However, we don’t have as many veteran trees as we once had. Recent data suggests that only 1 in 50 native woodlands have more than one veteran tree per 200,000 square metres (around the size of 28 football pitches) [1]. Without them, these features are being lost from our woodlands, leading to a decline in the abundance of invertebrates, birds, mammals and other species that rely on them.
As part of our wider restoration project in the Medlock Valley, we are responding to this through innovative habitat creation work known as tree veteranisation.
Tree veteranisation is the process of purposefully damaging or wounding younger trees to accelerate the formation of microhabitats. Cavities and nesting holes are manually carved in the trunk and branches to mimic the habitats created naturally by birds, storm damage or disease.
These habitats can take decades to form, which is why this work is so important. By creating these features now, we’re helping to provide spaces for species that might otherwise have to wait years for suitable habitats to develop naturally. This technique is only becoming more popular in the UK as we look for ways to replace the features that develop in veteran trees over time, helping to support the wildlife that depends on them. It is a practical way of restoring lost features within our woodlands and supporting nature recovery in the Medlock Valley.
How did we do it?
Tree veteranisation is all about creating the features that would usually take decades to form naturally. But how exactly do you go about turning a healthy tree into a future home for wildlife? Here’s how we did it in the Medlock Valley.
Step 1: Get a little help from our friends
As most of our work here at City of Trees tends to be on the ground, we had to enlist the help of our friends at TreeStation – Manchester-based arborists with the right knowledge and tools to help us get up into the trees and carry out the tree veteranisation.
Step 2: Acquire the right tools
On top of the gear to get up the trees, the most important tool we needed for this job is known as a piglet.
The piglet allowed us to hollow out the inside of a tree with more precision than a chainsaw ever could. Using the piglet, we were able to create smaller entrance holes. This precision means fewer gaps for air to get in and fewer wounds that the tree may fail to occlude (heal over) or invite disease. The piglet also creates a smooth nest interior, preventing animals from being injured whilst inside.
Step 3 – Pick our species: Homes for bats and birds
After getting to know the site in the Medlock Valley, we identified the potential to host a variety of bird and bat species. The river running through the woodland attracts insects, which creates a feeding ground for bats. On top of this, our initial site assessments showed that some bats already resided on the site, suggesting more would follow suit.
3a. Bat cavity creation
The bat cavity was hollowed out using the piglet. This creates a long, thin cavity for the bat to crawl deep down into and roost.
The rectangular wedge of the tree is then returned to the cavity and secured back onto the tree to create an airtight habitat.
All of our bat cavities face south; this is the preferred orientation for their homes, as it ensures they receive maximum sunlight and stay warm when roosting.
3b. Bird nesting holes
Installed at two different heights to accommodate for a variety of bird species, our bird nesting holes were hollowed out using the piglet. A nesting hole attachment was then secured to the nest opening. The birds require a smaller entrance to prevent predators from entering the nest.
At 4 to 6 metres, the nesting hole is suitable for coal tits. Further down the tree, at 1 metre, the slightly larger nesting holes are suitable for blue tits and willow tits.
Each entrance hole has a mushroom-like shape, which ensures a secure fit and promotes the main stem of the tree to repair and occlude the entrance hole fitting.
3c. Owl nests
The owl nest was the largest job and required the most work from the team. First up, we prepared a large poplar that the new owl home would sit in. We reduced the crown to ensure that it was clear of public footpaths if it were to fall. This will also promote bushy growth from the cut sections, providing shade and protection.
Like the bat cavity, a rectangular shape was carved out with suitable dimensions for a tawny owl.
The nest was positioned facing away from prevailing winds, and 100mm of wood chippings were left in the bottom of the nest, as tawny owls don’t bring their own nesting material to their habitats and often use existing nests, like those of woodpeckers.
Step 4: Look for existing wounds
In addition to creating fresh wounds, we identified some pre-existing wounds that can be carved into future bird homes. This process is known as rotting tree collar carving. With this hole facing upwards, a drainage hole was carved at the base of the nest to prevent waterlogging.
A decaying cavity is a great place to carve a hole, as the soft wood would normally be pecked and scratched at by animals; therefore, it creates a great natural habitat.
Step 5: Set up our cameras and wait…
After creating these new habitats, we need a way to see if tree veteranisation has been successful. So, we have set wildlife cameras at the newly created sites. This gives us a chance to monitor the new homes and see which nesting sites are popular with which species. This is vital data that can help us inform our future work in the area. And when we see our sites in action, we will be sure to share with you. To stay up to date, please click the link and follow along on our socials.
This work is part of a wider project with our partners at Groundwork Greater Manchester, The Conservation Volunteers, Canal & River Trust, Mersey Rivers Trust, and local councils to restore habitats across the Medlock Valley. This work is supported by the Species Survival Fund. The fund was developed by Defra and its arm’s-length bodies and delivered by The National Lottery Heritage Fund in partnership with Natural England and the Environment Agency. Read more here.