Ancient woodland is an ecosystem in which more threatened wildlife than in any other UK terrestrial habitat dwells. Across Europe, ancient woodlands are rare, but can be found in the form of remnants of “wildwood” or primeval forests, such as the Białowieża Forest on the border between Poland and Belarus, which once spanned the European Plain. But when does a woodland become “ancient”? And why is conservation important for these systems?
In England, ancient woodland is defined as woodland which has existed continuously since around 1600AD, or 1750AD in Scotland (Goldberg et al., 2007). Today, its cover across Britain extends over only 2%, when it was once the dominant habitat (covering up to 90% of the UK 6000 years ago) (Woodland Trust, 2000). This rapid decline occurred as a result of conversion to conifer plantation and clearance for agriculture especially over the last 100 years, providing wood for the war effort (encouraged by the Forestry Commission) and food for an ever-increasing population (Woodland Trust, 2000).
What makes an ancient woodland?
The plants which have adapted to live in ancient woodlands are different in many ways to those which have adapted to other types of woodland – they tend to be more shade-tolerant, avoiding overly wet or dry areas, and are generally more stress-tolerant (Hermy et al., 1999). A review of literature on the subject of plant diversity in ancient woodlands found 132 forest plant species with an “affinity for ancient forests” across Europe (Hermy et al., 1999). These include species such as wood anemone (Anemone nemerosa), Lily of the Valley (Convallaria majalis), Oxlip (Primula elatior) and the most well-known indicator, the bluebell (Hyacinthoides nonscriptus) (Fig 1).
“Ancient woods are valued as being among the most complex and diverse of ecosystems, and as having plants and animals that do not occur in woods of recent origin” – Rackham (2008)
Ancient woodland plants also share characteristics which make them particularly vulnerable to disturbances: they prefer habitat interiors (that is, the centre of habitat patches rather than the edges), have low dispersal ability (with 24% of European species dispersed by ants) and low reproductive potential (Hermy et al., 1999). According to Rackham (2008), ancient woodlands do not necessarily need ancient trees (the age at which a tree is considered “ancient” depends on the species), but may contain ancient coppice stumps, or multi-stemmed trees with large bases as a result of coppicing (Rackham, 2008). Old trees provide refuges for lichens, which are generally characteristic of primeval woodlands (Goldberg et al., 2007).
Threats to ancient woodland
Rackham (2008) highlights ten main threats to ancient woodlands globally. These include the usual suspects: fragmentation, depletion (removal of trees), climate change and invasive species, but also altered fire regime, disease, infilling of savanna, excessive numbers of deer and pollution. These threats have been outlined for their negative impact in woodlands globally, but some changes, such as climate change, are affecting species in different ways (and not always negatively). For example, the mixed effects of temperature, rainfall and aridity shifts act on different species according to their different tolerances, ability to migrate and colonise new habitats. This can be illustrated by the unexpected change in species distribution which occurred in Ken Wood, London, where a warm-loving hornbeam-oak wood migrated into a built-up area of London where the heat-island effect was stronger. (Rackham, 2008).
One threat of particular relevance to England is excessive numbers of deer. Deer populations across the country have been increasing for the last 200 years, because of increasing woodland area, removal of large predators, expansion of winter cereals (an important food source) and a reduction in livestock grazing, allowing a build up of browse for deer to eat and hide in (Fuller & Gill, 2001). The ecological impacts of deer are fairly well studied, and have been shown to affect all trophic levels –everything from trees to small mammals to ground flora and invertebrates (Fuller & Gill, 2001). Birds are also affected – overgrazing impoverishes woodland flora, which directly impacts low and ground-nesting birds (Rackham, 2008). Deer are therefore a key factor in the management of ancient woodlands, which must be considered to maintain woodland biodiversity.
“Increasing populations of deer have become one of the major forces of ecological change in British woodland” – Fuller & Gill (2001)
Conservation and management opportunities
Woodland management should focus on small changes in specific areas which have experienced losses, to ensure the overall health of the ecosystem (Goldberg et al., 2007). Hermy et al. (1999) state that forest management must aim at “favouring ancient forest plant species by maintaining traditional deciduous forest management systems” as a way to keep this natural diversity. But how will this be affected when considering newer unprecedented threats, such as that overgrazing by deer?
Deer control is difficult, due to the man power it requires – fencing can be effective, but requires maintenance. Culling has been shown to reduce damage in fields, but not in woods. Deer culling regulations are conservative, and often underestimate the number of deer at a site, making the culling quotas inappropriate. And then there is the question of how to determine the “right” level of browsing, or the “right” number of deer to be culled to obtain a balance. The deer problem is a complicated one, and has many potential solutions, including the reintroduction of predators, increased culling or increased cattle grazing as a replacement. For a real solution to be obtained, these suggestions need to be studied and put under the scrutiny of the public and the government.
Conservation of these woodlands is imperative, considering we have so little left, and its ecological importance for a range of wildlife. Not only must these woodlands be protected from the threats of agricultural conversion and land use change, but conservation must be adaptable to the changes we have yet to see with the current climate and the potential spread of pests and disease. The future of these wild places hangs in the balance.
Fuller, R.J. & Gill, R.M. (2001) Ecological impacts of increasing numbers of deer in British woodland. Forestry, 74(3), pp.193-199
Goldberg, E., Kirby, K., Hall, J. & Latham, J. (2007) The ancient woodland concept as a practical conservation tool in Great Britain. Journal for Nature Conservation, 15(2), pp.109-119
Hermy, M., Honnay, O., Firbank, L., Grashof-Bokdam, C. & Lawesson, J.E. (1999) An ecological comparison between ancient and other forest plant species of Europe, and the implications for forest conservation. Biological conservation, 91(1), pp.9-22
Rackham, O. (2008) Ancient woodlands: modern threats. New Phytologist, pp.571-586
Woodland Trust (2000) Why the UK’s ancient woodland is still under threat. [pdf] Available at: http://www.wbrc.org.uk/atp/Ancient%20Woodland%20Threats%20-%20Woodland%20Trust.pdf (Accessed: 28/07/2019)
Woodland Trust (n.d.) Why is ancient woodland special? [online] Available at: https://www.woodlandtrust.org.uk/about-us/ancient-woodland-restoration/ancient-woodland/why-is-ancient-woodland-special/ (Accessed: 28/07/2019)