|Certain woodlands can credibly be established as being
'ancient' through the study of old historical records such as
maps and estate records. Observations of landscape features such as banks, ditches and
other topographical features within a wood will also give clues to previous land use. By
surveying a number of these 'proven' ancient woodlands, species which are usually confined
to this type of habitat can be identified. Their presence can then be used to indicate
ancient woodland status in other less well-documented woodlands. The indicator species
chosen are commonly plants rather than animals. This is because plants are usually
conspicuous, relatively easy to identify and do not hide or absent themselves when humans
Most Ancient Woodland Indicator Species lists are
based on vascular plants (flowering plants, native conifers and ferns). These species are
known as Ancient Woodland Vascular Plants (AWVP). AWVP
scores (the number of these species present at a particular site) are frequently
considered in conservation work. Indicator species lists have also been constructed for
some areas using Bryophytes (mosses) and epiphytic lichens (those which grow on trees).
These lists of species provide extremely useful tools for ecologists
and conservationists in evaluating woodland habitats. However, they do need to be used
with a degree of caution. Lists of indicator species will vary according to geographical
location. This means that lists specifically worked out for a geographical area, such as
the Southwest of England, must be consulted if one is surveying in Devon. A list compiled
in Lincolnshire, for example, may give completely erroneous results in other areas of the
country. This is because local geology, soils, climate and history of land use will all
influence the plant species present and their ecological distribution. For example,
Hay-scented Buckler Fern, which is restricted to woodland in certain areas, is much more
common and widespread in mild, wet southwestern counties. It is therefore of less use as
an indicator in these regions.
In addition, the presence of a few relevant indicator species does
not mean that a woodland should be designated as 'ancient'. In general, the greater the
number of Ancient Woodland Indicator species occurring together in a wood, the greater the
probability that a woodland can be accorded this status. Below a certain minimum number of
species, few conclusions can be drawn.
||Indicator species are chosen for the following characteristics:
- They seldom occur outside woodland or, if they do,
they indicate long continuity of woodland cover.
- They are capable of growing in shade, although not
necessarily only in shade.
- They seem to be reliable indicators in at least part
of the region under survey.
- They are slow colonizers..
- A high AWVP score is a reliable indication of natural
- It also indicates ancient woodland, but does not on
its own constitute proof.
- Some woods which are undoubtedly ancient have a low
AWVP score. Study of other components of the woodland biodiversity such as lichens, or
invertebrates in rotting wood, may give clearer indications of ancient woodland status.
Quite often, ancient sites that are rich in AWVP's will be poor in lichens and rotting
wood invertebrates and vice-versa.
- Indices are also available based on epiphytic
lichens. There are about 30 species which are used as Ancient Woodland Indicators. These
can only be used where air pollution is not a problem and the trees are sufficiently large
for a diverse lichen community to grow on. This type of list can be particularly
useful in pasture woodland with open glades.
- Individual species should not be used solely to
indicate ancient woodland status.
- High AWVP scores are good indications of an ancient
woodland site, but are not proof on their own. They can however, be used to provide levels
of probability that a site is ancient.
- Not all indicator species are strictly limited to
ancient woodlands. For example, where secondary woodland adjoins older woodland, it will
acquire species associated with older woods much more quickly than isolated secondary
- Some plants tolerant of a wide range of ecological
conditions will behave differently on different soil types. They may be suitable
indicators of ancient woodland on one soil type, but not on another.
- Plants which are also cultivated in gardens (e.g.
Wild Daffodil) should be used with great caution.
- The development of indicator lists for particular
areas may involve so much work in initially identifying credible ancient woodland sites
from records, that the list is no longer required!
Examples of AWVP species
Sources of Information:
Francis Rose (1999) Indicators of
ancient woodland - the use of vascular plants in evaluating ancient woods for nature
conservation. British Wildlife: 10 (4) 241 - 251
George Peterken (2000)
Identifying ancient woodland using vascular plant indicators. British Wildlife: 11
(3) 153 - 158