Have you ever thought about habitat piles? Do you use this technique for tidying up after tree felling and woodland management?
Dead wood habitats, such as log piles and wood stacks, can have a valuable role, but they come with several issues.
Piles of wood and brash left on the woodland floor, or on heathland and scrub areas, can be used by nesting birds such as blackcap and willow warbler, as well as refugia for amphibians; whilst this would be a positive thing on a nature reserve, in another setting it could become a constraint to management. For example, one of our regular jobs is to advise on ecology issues at electricity sub stations and similar utility sites across the country. In these circumstances, bird nesting can restrict the essential maintenance of clearways along protective fences, and habitat piles can also create a fire risk or a means of unauthorised access over a fenceline.
It’s not just birds, fire and access issues. We have found piles of woody material left on top of features such as important woodland plant communities and badger paths, close to active setts; this level of potential disturbance is clearly something that we would try to avoid wherever possible. Part of the problem is that at certain times of year, the important ecological feature is not always obvious.
One other issue that comes with disturbance is the potential for spread of invasive plant species. Himalayan balsam, shown in the image below, is a species that thrives on ground disturbance and soil movement, both of which are often part of tree and woodland operations associated with development sites.
But what about areas in the wider environment? Are habitat piles and log stacks a management tool with some merit?
I wasn’t actually thinking about habitat piles when I set out to record the dawn chorus in a rather superb woodland nature reserve last week. The ancient, semi-natural, broadleaved woodland, which is a Site of Special Scientific Interest, is managed as a coppice with standards, and has coupes throughout at various stages of growth and development. I had been there in February last year to carry out an initial site recce, and the birdsong was already impressive, so I was confident that a visit in the middle of the breeding season would be something special.
I was carrying out a test of some sound recording equipment, this time a Zoom H3 VR (in contrast to the Song Meter Mini – see previous blog), and as I walked off the path looking for a suitable site, I came across several large piles of cut wood. When I came back to pick up the recorder the following morning, I decided to have a longer walk, and sure enough, there were piles of wood scattered throughout the reserve.
Some of these piles were taller than me and 2-3 metres wide. Historically, the produce from a coppice woodland would be of high value (otherwise why bother with this very labour-intensive practice at all?) and would form the basis of a woodland produce industry, with material perhaps being used for charcoal, building and tool handles. Originally, then, cut wood would likely all be used and the woodland could appear much more tidy (like an organised industrial site) than it would in modern times.
Trees lock up carbon – they are carbon sinks – anyone who has spent time reading about global warming could probably tell you that. Trees also store other materials, and together we might reasonably refer to all this stuff as nutrients i.e. things that other species could eat and digest, to help them grow. When a tree is cut down, the cut material starts to decay and the nutrients are released. In effect, the area with the cut material becomes more fertile and potentially this will support species which have a competitive advantage in areas with high nutrient availability. Nettles and goosegrass are classic examples of nitrogen-guzzling plants. But is this ok? Do we want to add what amounts to fertiliser to a woodland?
As anyone who has managed a reserve will tell you, a significant cost of habitat management is handling of waste products or by products – this can sometimes cost more than the original activity (such as tree felling) itself. So, it is understandable that an organisation might struggle to cope with the removal of a very large quantity of heavy, dense material, especially where this has been generated hundreds of metres from the nearest access point.
Tidiness and trouble brewing
There is no doubt that with both development sites and our many small, isolated reserves in the UK, we are necessarily habituated to micro-manipulation of habitats – what amounts to gardening on a grand scale, albeit to fulfil very worthy conservation aims. This approach, where everything has its ‘correct’ place, often leads to over-tidiness, which is perhaps one reason why the practice of generating habitat piles is so easily adopted.
As much of the work that generates log piles takes place outside the growing season, in winter months, we may not be aware of the impacts on vegetation until much later on. This is when growth of species such as variegated archangel becomes obvious, but are we still involved by this stage and able to deal with it?
And in our nature reserves, just as we have stored or singled coppice in some woodlands with the promise of future resources, habitat piles can store nutrients released slowly with future issues, but do we wait long enough to see the impacts of our efforts? Rather like unintentional disturbance to bats during surveys in winter, the impacts of our actions may not be seen until much later, and when we realise the mistakes, it can be too late to rectify things. In fact, the results of nutrient release may not be obvious for a long time – long enough for a change of manager, a new management plan or for the original notes of a previous management action to be lost altogether.
What to do?
Generating piles of materials is usually a convenience and in our experience is rarely a goal in itself. This cut material can be highly valuable as a management resource if used effectively and for a defined purpose.
How cut material accumulates and the role it plays will be different, depending on the management history, habitats present and the goals of the site owners. It’s definitely worth spending a bit of time thinking through all of these before making a final decision – large piles of wood and brash are unlikely to be moved again once deposited.
And if you ever unsure about the role of dead wood or how it accumulates in a given habitat, just spend time looking around. It should soon be obvious if you are creating an issue.
Footnotes:
Coppice – Coppicing is probably the earliest form of structured silvicultural management, and relies on the ability of many species of tree to regenerate from cut stumps or ‘stools’. It primarily involves cutting either a tree or existing coppice stool to encourage re growth from the freshly cut stumps to produce many small stems per tree or coppice stool. The many stems are in turn harvested on regular short rotations. Most of our native trees will coppice well, with the most common species including hazel, ash, oak, alder and field maple.
Stored and singled coppice – tree management in coppice woodlands sometimes involved the removal of all but the best stem (straightest and vigorous) from each stool. This operation is known as ‘singling’ and the stems grown on to form large trees which are known as ‘stored coppice’.
Coupe – Coppice is normally divided into coupes (otherwise known as a fell, a cant, a hagg, or more simply a compartment).