|Ancient Woodland Holywell Dene (Wikipedia)|
The threat to Britain’s ancient woodland has been much discussed recently, the suggestion being that where they are lost to housing development they might be replaced with new woods through biodiversity offsetting schemes.
This issue will need to be addressed, particularly in relation to HS2, the route of which is likely to cut through or close to about 60 ancient woods.
So what makes ancient woodland different? After all, 40 years ago the term was virtually unknown, even in conservation circles.
Where are the ancient woods?
The concept of ancient woodland was developed in the 1970s by Oliver Rackham at Cambridge and George Peterken, then of the Nature Conservancy Council.
The aim was to help identify and conserve sites likely to be rich in woodland plants and other rare or endangered species, but it was recognised that ancient woods also had a significant cultural value, having been managed sustainably for centuries using traditional practices such as coppicing.
In 1981 Peterken initiated the process of drawing up an inventory of all woods greater than two hectares in Britain that could be classed as ancient because they had been continuously wooded since 1600 (1750 in Scotland).
Evidence for continuity came from old maps or references in historical records, evidence of long-standing traditional management and, if available, records of plants that are generally slow to spread to new woodland, such as herb paris.
The inventories were compiled between 1981 and 1991; prior to the ready availability of the internet and Geographic Information Systems they were collated using tracing paper, coloured pencils and a lot of temporary staff time.
In only a few cases was there evidence that the wood was definitely present as far back as 1600, so the working presumption was that if it had existed in 1800 then it was likely to have existed in 1600, in the absence of evidence to the contrary.
The maps are not and probably never will be completely accurate, but the process identified over 20,000 ancient woods in England covering over 350,000 hectares; they are present in most 10km squares.
Ancient woodland was recognised as a distinct category in national forestry policy in 1985, and consolidated in revised forestry and planning policy guidance in 2005.
Why are they special?
The original idea was that ancient woodlands are special, valuable places that should be protected. Ancient woods tend to be richer in biodiversity, and harbour more uncommon plants such as toothwort, hay-scented fern, or the goldilocks buttercup than more recent woods.
Such species tend to be poor at spreading through the countryside, so it may take decades or centuries for them to reach new woods. In addition soil conditions in new woods are different because they are usually created on farmland that has been ploughed and fertilised.
However some ancient woods have been heavily disturbed in the past and are species-poor. And equally, sometimes new woods boast more species associated with older forests than expected.
Woodland archaeologists have confirmed that ancient woods often contain banks, ditches, and remains of old settlements that add to the reasons why they should be conserved, while also casting doubt that they have an unbroken link back to the wildwood, the landscapes that developed in Britain after the last ice age.
Today’s threats to woods
So where does ancient woodland conservation stand today? The main threat prior to 1980 was the wrong forestry practices - many were replanted with conifers, or were neglected such that they became too dense.
That is being addressed through the encouragement of more sensitive management. But the building of new roads, housing, and quarries remains a significant threat, although it affects only a small number of sites across the country.
The National Planning Policy Framework includes a stronger statement against development than for most other habitats:
Planning permission should be refused for development resulting in the loss or deterioration of irreplaceable habitats, including ancient woodland and the loss of aged or veteran trees found outside ancient woodland, unless the need for, and benefits of, the development in that location clearly outweigh the loss.It is not absolute protection, but even protected sites of European importance do not have that guarantee.
Ancient woods are irreplaceable, but they are not all of equal value: a few trees on a housing estate with little in the way of woodland species beneath, even though they are the remnants of an ancient woodland, does not have the same significance as Monk’s Wood National Nature Reserve.
Nevertheless threats to even small ancient woods are regularly contested at planning inquiries and often won.
Where the case is lost then biodiversity offsetting should come in to play, but at the right level. If two hectares of ancient woodland is lost, then two hectares of new habitat as compensation would be laughable. Suppose the offer were not two but 2,000 hectares, and an appropriate endowment?
This could provide a potentially greater, albeit different, legacy of biodiversity to that lost. But such a ratio is unrealistic - the “right level” will lie somewhere in-between.
The challenge is to make sure that the level of biodiversity offsetting is high enough that it is a genuine net biodiversity gain: the costs involved may then also discourage developers from going near ancient woods in the first place.
Keith Kirby was previously employed by the Nature Conservancy Council and its successor bodies as a woodland ecologist, in part responsible for producing the ancient woodland inventories. He is now affiliated with Plant Sciences Department, Oxford.
This article was originally published at The Conversation. Read the original article.