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13 Jul 2018

Tree and bat surveys at Inverewe

Written by Ian Williams, Highland CV Group Leader
Tree surveying at Inverewe
Inverewe is much more than its spectacular garden: there are also 800 hectares of varied countryside, much of it wooded, with a large number of plant and animal species.

A project is currently being undertaken to survey the trees so we can quantify the forest structure and the environmental benefits that trees provide. This includes the value they contribute to Inverewe in terms of ecosystem services – biodiversity, carbon capture, temperature effects on buildings and water uptake.

The Highland National Trust for Scotland Conservation Volunteer Group assisted with this survey over two days, and here Ian Williams, CV Leader for this project, tells us more about it:

‘We surveyed all the trees within the immediate confines of the buildings and car park, then surveyed sample areas from the wider estate. Working in pairs, we measured the vital statistics of trees – trunk diameter, height, canopy width and height of the canopy base from the ground. Then we had the more challenging task of estimating how much of the crown is missing and how healthy the remaining crown is. This can be a bit subjective but it’s easier to reach an informed assessment when there are two of you.

‘Visitors to Inverewe were very interested in what we were doing, particularly how we measured the height of some of the very tall trees. This involved using a clinometer aimed at the top of the tree and moving it to a point from the tree when the clinometer is at 45 degrees. You then measure the distance from where you’re standing to the middle of the trunk; finally, by adding your height you get the height of the tree. For the mathematically minded among you, this forms an isosceles right triangle.

‘At the same time, we worked with staff to conduct a bat survey to determine where bats are feeding across the estate. Armed with bat detectors, we walked a set route and noted the number and type of bats we saw or heard with the detector. The main species found here are the common pipistrelle (Pipistrellus pipistrellus) and soprano pipistrelle (Pipistrellus pygmaeus), although brown long-eared bats (Plecotus auritus) have also been recorded in the past. Common and soprano pipistrelles are most readily distinguished by their echolocation calls being at different frequencies to each other. Having established the key roost sites, the survey data is collated into a heat map, which enables us to see how they move through the landscape.’

Ian says: ‘I volunteer first to make a difference. Many tasks would simply not get done without the help of conservation volunteers and it’s extremely satisfying to see the results of our hard work. Secondly, there’s great camaraderie among the volunteers, who work well as a team. The banter and team spirit are just so rewarding that it makes you feel good. Finally, I get a bit of exercise, which buys me a few more heartbeats.’

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