Tree management usually involves growing trees for a saleable product, such as timber, or undertaking work to prolong the life of a tree. The increasing awareness of the value of trees has shaped tree management over recent years. Features that were once viewed as signs of ill health and typically removed, such as deadwood, are now retained for their wildlife value. Whether it’s lichens growing on bark, insects feeding on decaying wood or birds nesting in hollows, the wide range of wildlife species are integral to the functioning of the natural world.
But what if tree management went one step further, and instead of simply retaining features used by wildlife, it created them? This is exactly what bat researcher Jim Mullholland is trying to do for two of the UK’s rarest bat species. We caught up with Jim to find out more.
“The UK is home to 17 species of bats. Some are relatively common, whereas others are rare. The reasons for the differences are varied, however one key theme is the loyalty bats show to their homes (known as roosts). Unlike birds, who create a new nest site each year, bats will return to the same roosts year on year. When roosts are lost, this has an impact upon local bat populations.
In the UK bats and their roost sites are protected, making it illegal to harm bats or damage/destroy their roosts. This protection has improved the prospects for some species, although recovery is slow. This slow recovery is in part due to the fact that bats are slow to reproduce, only giving birth to one young per year.
Unfortunately, other species have not fared as well. Two of the UK’s rarest bat species, Bechstein’s and barbastelle bats, are woodland specialists and are heavily reliant upon trees for roosting. With increasing pressures on natural environments through changes in agriculture, development and a need to manage risk from falling trees, suitable roost trees are becoming increasingly scarce.
Standard bat conservation measures for these species have relied upon bat boxes, or perhaps resurrecting hollow branches. Whilst these techniques have had some success, nothing replaces a hollow tree as bat roost. Various studies have shown that the temperature and humidity profiles of bat boxes differ from natural cavities, making them less suitable for mothers to rear their young.
This got Jim thinking: would it be possible to create suitable roosting conditions in living trees? A similar approach has been used to create wood-decay habitat for saproxylic species. Saproxylic (literally meaning ‘feeding on wood’) includes a large number of insect, fungi, bird and mammal species. One of the most iconic is the stag beetle (Lucanus cervus), the larvae of which live in decaying tree roots before emerging as adults.
With support from the People’s Trust for Endangered Species, the Arboricultural Association and STIHL, a five-year research project was born. Jim explained more:
“Inspired by work focussed on deadwood species, we came up with the idea of cutting holes in trees specifically designed for bats. First, we worked with foresters to select suitable young trees. These trees were of low economic and wildlife value and would have otherwise been removed as part of standard forestry practice.
With suitable trees identified, we researched the roosting requirements for both Bechstein’s and barbastelle bat. In summary, Bechstein’s bats like tree cavities, with a particular preference for woodpecker holes, whereas barbastelle bats prefer splits, cracks or flaking bark.
For each species we created what we are calling ‘instant’ and ‘future’ roosts. Instant roosts are essentially a bat box in a living tree. Future roosts are created by wounding trees in such a way that they develop roost features over time. This recognises that in conservation sometimes we need immediate solutions and other times we are interested in the long game. Instant features, as the name suggests, are suitable from the moment they are created. We expect future features to take around five years to mature and offer suitable conditions.
As we are working in woodlands with these rare bats, I was keen to keep any disturbance to a minimum; we don’t want to scare the bats off before they have a chance to find the new roosts! With advances in battery technology, the obvious choice was battery-powered chainsaws and, as a life-long STIHL fan, I knew exactly where to go to find the right tools. We use a combination of the STIHL MSA 161 T and MSA 220 C-B for the work, between these two cordless chainsaws we have the power and flexibility we need.
We hope that our work will provide a valuable conservation tool that can be used to help protect and enhance woodland bat populations. In the future, we plan to deliver training on the techniques we are using. The battery chainsaws will provide a superior learning environment, compared to petrol chainsaws, allowing us to hold conversations with trainees whilst someone is working in the tree.”
The new roost features were created in early 2021. Jim and his team will spend the next four years monitoring these features to see if, and when, bats take up residence. We can’t wait to find out what happens!
You can find out more this vital conservation work at https://www.batlicence.co.uk/2020/07/06/improving-the-future-for-two-tree-dwelling-bat-species/ or https://ptes.org/grants/uk-mammal-projects/monitoring-tree-roosts-for-bats/