Beetle monitoring: How dead wood is supporting new life

Posted: 12th June 2020

Peter Cairns /

It only takes a few minutes of walking through a healthy Caledonian pinewood to see what a complex, dynamic place it is. From areas of dense canopy cover to sunny clearings. Young saplings to ancient ‘granny’ pines. Trees as straight as bean poles to others gnarled and twisted, with ferns growing from their branches. You would also see an impressive number of dead and dying trees – deadwood – some standing tall like statues, others lying on the forest floor, perhaps covered in moss or with fungi growing from them.

Such deadwood is an essential part of a healthy forest. It is home to a great array of flora and fauna, which together play a vital role in recycling nutrients through the forest ecosystem, as well as being sources of food for other creatures. Deadwood also helps to stop erosion, especially in streams where it slows down the flow of water. The number of species that live in or on deadwood is staggering – in the UK alone, there are more than 2,000 deadwood invertebrate species. These species not only support birds, mammals, plants, fungi and mosses – there are even fish that rely on deadwood habitat in streams!

In forests that have been planted for commercial timber production, the deadwood resource tends to look quite different to what’s present in more natural woodland. For instance, deadwood might be concentrated in a few small pockets rather than being spread throughout the forest, or there might be lots of small pieces of deadwood but fewer large dead trees. With the volume and variety of deadwood often being far lower in former plantations, restoring them to healthy forests therefore often involves adding to the deadwood resource, both by actively killing trees and by simply leaving trees in situ (on site) when they die naturally.

‘Ring barking’ is one method of deadwood creation being used by the Cairngorms Connect team to restructure areas of plantation. Photo credit: Cairngorms Connect.

Such ‘deadwood creation’ and ‘plantation restructuring’ methods are being used across the Cairngorms Connect area to address this imbalance.  To find out how well this is working to restore the forests to healthier, functioning ecosystems, the project team are monitoring one particularly crucial group of beasties: deadwood beetles (that is, beetles that rely in some way on deadwood). In the UK, there are 650 different species of deadwood beetle that we know of, belonging to 53 families. Some of these species eat the dead wood itself, others rely on the fungi and moulds that live on the wood – some of them even farm fungi for food, inside the deadwood!

Steininger bottle trap hanging from a Scots Pine tree in the Cairngorms Connect area. Photo credit: Cairngorms Connect.

Cairngorms Connect will be measuring the abundance and diversity of deadwood beetles in former plantation forests where new deadwood is being actively created, and comparing this with the beetle abundance and diversity in areas where no active deadwood creation is taking place. In both types of forest, naturally arising deadwood is being left in situ, so the team will also be monitoring the natural accumulation of deadwood over the course of the study. They will be repeating the monitoring in nearby areas of semi-natural forest, to help understand how much further they still have to go in achieving the ultimate goal of restoring plantation forests to habitats that effectively look and function like natural Caledonian pinewoods.

To monitor beetles, the Cairngorms Connect team are using a simple DIY type of flight interception trap. Traps like these are a common way of surveying flying insects in forests, as they let you compare what’s living in different trees or habitat patches in an objective, unbiased way. The design they’re using was originally developed in the US by Steininger and colleagues. The traps are cheap and easy to make out of an old 2-litre fizzy drink bottle, making them ideal for school projects and citizen science too! Insects accidentally fly into the clear plastic panel and then fall down into the collecting fluid below. Every month, the team empty the traps and replace the collecting fluid, then take the samples back to the lab to identify the collected insects.

The team are excited to see the results of this work over the next few years. As well as tracking how their management work is affecting the numbers and types of beetles present, this monitoring may shed light on other questions such as whether there are beetle species living in the area that they didn’t even know were there!

This research forms part of the Cairngorms Connect science and monitoring programme which is essential to assess the impact of restoration work and look at future ways to help with landscape scale restoration towards healthier and sustainable habitats. To find out more, visit the Cairngorms Connect project page.

A version of this article first appeared on the Cairngorms Connect website, and was written by Dr Pip Gullet – Project Scientist at Cairngorms Connect.

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