Guidance on dealing with the changing distribution of tree species
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Natural England Technical Information Note TIN053
Guidance on dealing with the
changing distribution of tree species
Native tree species are considered to be of higher value than non-native species for
nature conservation because they are a link to the original natural conditions and are
more likely to create and support the conditions needed by other elements of the
natural woodland system. However, the definition of what should be considered
native is the subject of debate. This note explores the issues and recommends a
flexible approach to dealing with non-native species that are native on the near
continent and which may naturalise in England. This approach should help reduce
unnecessary conflicts in woods where there are other objectives, for example
landscape, recreation, historic or wood production, for which the distinction between
native and non-native species is less important.
Background In previous inter-glacial periods a wider range of
From a nature conservation point of view a high tree and shrub species were present in the
priority is given to maintaining the native trees British Isles.
and shrubs in our woods, because they provide
a link to original natural conditions and are more As a consequence of expected climate change
likely to create or support conditions needed by the distribution of tree species will alter in the
other woodland species in England. For example future. It is unclear precisely what these changes
in the generic guidance on setting conservation will be. However, Natural England is
objectives for woodland Sites of Special encouraging habitat networks and increased
Scientific Interest the target is predominantly landscape permeability. We are therefore
95% native tree and shrubs, although this can encouraging species to move between sites.
be varied for particular sites. The same This could include spread to areas where they
approach is generally applied to other sites of do not currently occur (ie are not currently locally
high nature conservation value. However, this native), and this will lead to changes in the
may lead to potential management conflicts with woods into which they spread. Assisted
visual, cultural, wood-production or historical migration might also be considered for some
objectives, where the distinction between native non-mobile species on account of the rate and
and non-native species is often of lesser or no magnitude of predicted climate change. At the
importance. same time there may be losses of species or
reduction in their abundance in other regions.
How native is defined depends on what
geographic boundaries and what time periods Changes in species distribution are seen as part
are considered. Beech is native to Great Britain. of the process of the nature conservation
At a finer scale it is not native to Scotland, but is adaptation to climate change. It therefore
to England and Wales. It is native to southern becomes illogical to automatically rule out the
but not the extreme west of England, to south- spread of species that are not currently native,
east but not to northern Wales. Similarly Scots but which do occur on the near continent. Many
pine is native to Great Britain, but there are no of these have already been introduced into
recent native populations in England or Wales. gardens and plantations and have
naturalised to varying degrees.
First edition 5 March 2009
www.naturalengland.org.ukNatural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
While such naturalised stands have almost may increase the potential richness of the
certainly originated from planted individuals it is woodland. Alternatively their presence can be
impossible to be sure that sycamore could not part of the evolution of the site towards a future-
have spread naturally into southern England natural/future cultural state. Any action taken to
from northern France in the last millennium, for remove them may create damage or disturbance
example, through seed blown on an exceptional to the site.
south-westerly gale.
There is a balance to be struck between more-
Thus, while in most cases it is reasonably clear or-less intensive intervention to remove the
what is native in any particular area, there are species and the future losses or gains from
some species whose status is less clear-cut, for leaving them alone. The same arguments apply
example because: to the treatment of native species whose
abundance is changing significantly (eg ash) and
They are very long-established introductions which have the capacity to alter the character of
that have naturalised at least at some sites eg a woodland (eg holly).
sweet chestnut in Kent.
The limits of their past native distribution are The approach set out below is based on
debateable (beech in the north). three elements:
The species was present in an area but has 1 The nature conservation value of the site
been absent for many centuries (Scots pine in
northern England). Management of colonising or spreading species
should have a higher priority:
The distribution/range of a species is changing
or expected to change substantially as a
In sites notified for a particular woodland type
consequence of climate change (beech).
rather than in non-designated sites.
The current populations are clearly planted or
In semi-natural woods rather than in
are derived from plantations in the last 200
plantations.
years.
In ancient woodland rather than in recent
These issues are discussed in more detail for woodland.
particular species in the section, The status and Where there is no particular cultural, social or
distribution of selected species in England. historical value attached to the colonising
species at that site.
Debate or ambiguity on the status of a species in
an area can lead to inconsistency in the advice 2 The degree to which a particular species
that staff give on how to treat these species. changes the nature of the site
Determined by the tree characteristics, rates of
Much effort could be spent on assessing the regeneration and other factors, for example:
precise status of these species without
necessarily coming to a consensus, because the Replacement of one dense-shading species by
evidence may be missing or ambiguous. It may another will have less of an impact than where
therefore be more productive to assess such the new species casts much more shade than
species primarily in terms of the impact that they the species it replaces.
are having on the particular site in question in Conifer replacing conifer is likely to cause less
relation to the nature conservation objectives change in shade than conifer replacing
(whether formal or informal) for that site. broadleaf.
On any particular site a species that
A site-specific framework for dealing with
regenerates freely is more significant, because
spreading or introduced tree species of potential future impacts, than one that is
Tree species whose ranges are increasing will unlikely to regenerate.
alter the composition of the sites that they
colonise to varying degrees. In some cases they
Page 2Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
Does the species replace another as host for Where there are other major seed sources in
a rare or threatened species? (For example old surroundings such that ongoing work would be
sycamore trees may be hosts for lichens needed to prevent further regeneration.
previously found on elm). In minimum intervention stands.
3 Resources Presumption towards management of a
The ease and cost of control needs to be species in a particular site:
proportionate to the likely impact or threat: Where the stand being invaded is of high
conservation value, with species or
Management before the species has assemblages that would be impacted by a
significantly altered a site is a higher priority change of species and:
than where the species is already long-
established and changes to the woodland The new species is present in small amounts,
assemblage have taken place. which could be eliminated readily and without
One-off operations, or management that is part causing significant damage.
of work that will be taking place anyway, are The new species is present in amounts that
more justifiable than those where extensive can be eliminated as part of ongoing
and on-going work will be needed specifically management that would be undertaken
to manage the new species. anyway.
Where there are largely young stems or young
None of the above should be taken as absolute to mature stems showing little regeneration.
presumptions for or against management of a Where there is no significant seed source in
particular species and most are consistent with surroundings.
what is already accepted practice in some areas.
For example, it is similar to the approach
In actively managed sites.
adopted towards sycamore in the LIFE Ravine The result will be three types of site:
Project Management Handbook.
Sites where the aim is to maintain the past
Decisions at a site level should therefore be native tree and shrub composition as closely
along the following lines as possible.
Sites where a change of species is accepted
Presumption towards acceptance of a alongside conservation of the main features of
species in a particular site: interest.
Where the impact on characteristic species or Sites which are managed or allowed to
assemblages has already happened or is not develop towards a new state which may
likely to be significant. contain different suites of species.
Where mature or veteran trees of the new
species are present, especially if they are part The status and distribution of selected
of uneven age structured population. species in England
Where the species is already widespread in This section explores how the approach above
the stand or wood, having largely replaced the might apply to particular species in different
former type, and is showing good parts of England.
regeneration.
Where high level of management (particularly Beech in northern and western England
ongoing management) would be needed to Past distribution
remove the species, especially if this would be The species first appeared in Britain fairly early
the main reason for having to carry out the in the post-glacial period, but the records
management. remain sparse for several thousand years. It
Where the management to control the species appears to have not been very competitive in
would cause significant other disturbance.
Page 3Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
the wildwood, possibly because Britain is its range and abundance declines in southern
towards the edge of its range. Europe.
The main spread and increase in abundance
occurred around the Neolithic period and may Consequences of increased beech in
have been facilitated by human disturbance woodland
and clearance of the wildwood. Even so it may Beech regenerates well under higher levels of
never have reached the climatic limits of its shade than oak or ash and has the potential to
potential range. become the canopy that is dominant across a
As a major forest type, beech seems to have wide range of soil types. The production of
been limited to southern Britain and there is beech mast (seed) is irregular which will slow
evidence for continuity of beech woodland spread in woods. However, it may become
presence through to the present in these more common if summers become warmer.
regions. Beech woodland conservation is There is evidence of a high frequency of mast
therefore focussed on these regions, see maps years in southern England over the past ten
of beech woodland types in Rodwell (1991), years.
Peterken (1980), Rackham (2003). The seed tends not to spread widely from
There are outlier pollen records further north parent trees so often there will be clusters of
and west in England, some of which may have beech and then relatively large areas with little
represented local populations, rather than regeneration. Parent trees outside the site are
long-distance pollen transport, but with no therefore less of a concern in assessing impact
evidence for continuity of beech woodland or than for some other species.
veteran trees. Regeneration is limited by grazing (as is that of
The oldest trees tend to be in designed parks other species).
or other situations where the trees seem likely Beech casts one of the heaviest shades of
to have been planted. broadleaved species. Particularly on acid sites
Veteran beech trees seldom survive more than the ground flora and shrub layer (other than
350 years, so survival of individuals from the holly) can be greatly reduced in cover and
early medieval period is unlikely. richness.
There is some overlap between the ground
Future distribution flora and shrub layer found under beech and
Beech has been widely planted in north and that found under oak or ash, but but under
west England (and also in Wales and beech there is reduced cover and frequency
Scotland) over the last 300 years and has (Rodwell 1991).
locally naturalised. The assemblages that do develop under beech
Given that beech may not have reached its beyond its current native range are not
climatic limit before humans disrupted the dissimilar (allowing for climatic and soil
landscape, the natural spread or re- variations) to those that occur in southern
colonisation (if the outlier pollen records did Britain, but some of the rarer beech woodland
represent past populations) of northern and specialists may be missing (Wesche and
western England could still be happening, others, 2007).
albeit masked by the effects of planting. Beech can develop a rich deadwood
Changing climatic conditions may put beech invertebrate fauna and in some sites in
populations in southern England under northern England (Dunham Massey,
increased stress and it may not be possible to Duncombe Park) the veteran beeches are a
maintain the current levels of beech in some significant part of the interest.
sites. Most models suggest that conditions for Old beech in the north is not particularly rich in
beech in north-west England will remain lichens (Francis Rose personal
favourable or improve. The significance of communication).
beech populations in Britain may increase if Beech woods are considered rich in fungi but
(as is likely from climate change projections) there are no known systematic surveys
Page 4Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
comparing the richness of northern and recently it has been a significant part of woods
southern beech woods. or as trees in the landscape.
Preliminary assessment Future distribution
Long-term dominance by beech is not Sycamore has been widely planted particularly
inevitable in all sites, so concerns about beech in north and west England (and in Wales and
takeover should be based on the actual Scotland) over the last 300 years and has
regeneration occurring on the site. locally naturalised. It is a characteristic feature
The impact of increasing beech dominance will of Pennine farmsteads and is likely to remain a
be most significant where there are rich and significant part of future landscapes.
important ground layer communities, whether It regenerates freely, particularly on moist
of bryophytes on acid soils or higher plants on neutral to base-rich soils; it is more likely to
base rich soils. spread on such soils, rather than on acid soils.
Veteran beech should be maintained for their It is relatively shade-tolerant; hence it is
contribution to the deadwood communities. capable of spreading within existing woods.
If the distribution and abundance of beech is Some studies suggest that regeneration tends
responding to climate change, accepting more to follow soil disturbance (work by Neil Riddle
beech in woods in the north and west is 2005, summarised in Ravine Woodland
anticipating the process of climate change Management Handbook).
adaptation. The changes in ground flora and Trees seed regularly and spread quite well,
other woodland components are a further again encouraging spread. Some studies
consequence of this. suggest possible alternation of regeneration
The cultural value of beech varies. On some with ash (Waters and Savill 1991).
sites it has been an important contribution to Regeneration is limited by grazing (as is that of
the cultural landscape (eg of designed parks) other species) .
in other cases it may be diluting the traditional The growth of sycamore may be reduced
landscape eg oak coppice landscape. under future droughts compared to ash, which
may encourage co-existence with ash and oak
Sycamore in some sites (Morecroft and others 2008).
Past distribution
The species is first definitely recorded in Consequences of increased sycamore in
Britain in the early medieval period (Jones woodland
1945). There are claims for earlier occurrences Sycamore regeneration tends to develop first
(Green 2005), but the evidence for this is into a dense pole-stand understorey and then
ambiguous and there is a difficulty in into even-aged patches of mature timber with
separating its pollen from that of field maple. little understorey. Existing shrub layers may be
There are some early archaeological finds. lost through shading.
However, these are not convincing, for The ground flora is often rather uniform under
example the early medieval leaf carving on St mature sycamore (eg a carpet of Dog’s
Frideswides tomb (Oxford) could have been mercury) but this may be more to do with the
carved by a French mason, or a local mason tendency for these to be mature high forest
who had seen the tree in France. A fourth stands, rather than the effect of sycamore
century Roman bucket of sycamore occurs at shade per se. Ground flora richness may be
a site which also contains other finds including maintained in other situations (Taylor 1985;
silver fir and quern stones from Germany. Riddle 2005).
If sycamore did occur pre-Medieval times it On the continent sycamore is a characteristic
would appear not to have been abundant component of the Tilio-Acerion Habitat
enough for anyone to notice, compared to Directive type. In some British sites it may
more regular records from the seventeenth occupy situations where either lime or elm
century onward. It is only comparatively would previously have been dominant.
Page 5Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
However, it is unlikely to out-compete either Sweet chestnut
species where these are healthy. Past distribution
Old sycamore can have a rich lichen flora Sweet chestnut was probably native originally
distinct from that on oak on similar sites. to the Balkans and parts of south-central
Veteran sycamore can provide valuable dead- Europe. However, its value as a food source
wood habitat. as well as for its wood meant that it has been
Its reputation as poor for invertebrates is widely spread throughout the rest of Europe,
based on a particular study of specialist not least by the Romans.
faunas. It is richer than some native species Rackham (2003) discusses the early
and can carry a high biomass of invertebrates, controversy over whether or not it was native
which may be more significant if food for birds and the eventual conclusion was that it was a
and mammals is a consideration. Roman introduction. However, he treats it as
an honorary native at least on some sites,
Preliminary assessment particularly in Kent and Essex and locally
Long-term dominance by sycamore is not elsewhere in the south-east and the Welsh
inevitable, so the actual regeneration occurring borders. The earliest localised record is in the
on the site should be assessed. Management reign of Henry II in the Forest of Dean.
to remove existing trees may create the Its value, particularly as coppice, led to it being
disturbance that favours increased sycamore widely planted throughout the lowlands. It was
regeneration. also managed as pollards and as ornamental
The potential impact will be most significant trees in parks.
where there are rich and important ground
layer communities of higher plants on base Future distribution
rich soils and where it is replacing ash, rather Although widely distributed the woods where it
than former elm sites. is abundant are relatively rare. In most
Its reputation as having a low associated fauna instances the trees or stools have been
has been challenged. planted. Natural regeneration and spread tend
Veteran trees should be maintained for their to be limited, not least because the nut crop is
potential lichen and deadwood interest. not very good in England. With increased
On the continent sycamore is frequently summer temperatures nut set and natural
associated with relatively cool, moist regeneration may improve.
situations, such as gorges. Some of these may The recent advance of chestnut blight
become under stress under future climate Cryphonectria parasitica in northern Europe
scenarios, with an expected range shift to the suggests strongly that it will extend its range
north and west. Allowing some spread in into Britain. If it does the impact could be to
British woodland is compatible with the reduce the dominance of chestnut in woodland
process of climate change adaptation. in southern England.
It has the potential to spread from parent trees Rackham considers it predominantly a tree of
in the neighbourhood. However, provided there acid soils, typically on sandy or silty soils, but
is little ground disturbance the significance of Buckley and Howells (2004) suggest that it can
such spread may be limited. By itself this is not occur on a wider range of conditions.
a reason for not managing the species where it
is considered to be undesirable. Consequences of increased sweet chestnut
The cultural value of sycamore varies: in many in woodland
non-woodland situations it is an important part Chestnut stands are often poor in vascular
of the local landscape - particularly as non- plants, partly because of the nature of the soils
woodland trees in northern England. Also on which they occur, but also because of the
sycamore coppices were associated with the density of its shade, frequently compounded
bobbin mills of the north-west. by its growth as well-stocked coppice. In
addition its litter, composed of large, slow to
Page 6Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
decay leaves, may suppress some smaller provide a better economic crop and the
ground flora species. coppice is more likely to be worked. The aim
The shrub layer, other than coppice regrowth, should be to achieve structural diversity
also tends to be poor, again because of the through the coppice system.
competitive nature of chestnut. In other stands management should allow or
The value of chestnut coppice means that it is encourage the gradual diversification of the
more likely than many other species still to be composition through spread of other tree
worked, and there are benefits from the species (usually oak and birch).
diverse structures that this creates.
There appear to be few species strongly Holm oak Quercus ilex
associated with the tree. Past distribution
Veteran chestnuts can provide valuable dead- This is primarily a Mediterranean species,
wood habitat and are a significant component although it occurs into central France.
of the interest at sites such as Croft Castle. It has been cultivated in Britain since the 16th
century, widely planted in the 18th century and
Preliminary assessment was recorded in the wild in 1862 (Preston and
To date chestnut has not been viewed as a others 2002).
particularly invasive species in the way that
sycamore or beech in the north have been. In Future distribution
future this may change, although increased It currently occurs through much of southern
invasiveness might be countered by increased England and appears to be spreading.
attack by chestnut blight. It is likely to be favoured by climate change.
Where sweet chestnut becomes dominant the It seeds prolifically and can regenerate freely
effects are likely to be reduced ground flora on appropriate soils.
abundance under the canopy. However, if it is
managed as coppice this effect may be off-set Consequences of increased holm oak in
by increases in ground flora in the recently cut woodland
stands.
As an evergreen species it changes the
The woods where it seems most likely to character of the woodland community in a way
spread are oak-bramble-bracken (W10) and that the species discussed previously do not.
oak-wavy hair-grass (W16) woods. However, The nearest native equivalents are stands of
its impact on these communities is likely to be yew and holly.
less than its impact in ash (W8) woodland.
There is very limited information on the
Locally the species has high cultural value. For ecology of the species in Britain, but casual
example it is associated with hop production in observation at Lyme Regis Undercliff suggests
Kent and the Welsh borders. that the ground flora underneath it is likely to
Where it is a long-established component of become dominated by ivy, ferns and a scatter
the wood (>200 years) there is no particular of other highly shade-tolerant plants.
reason not to treat it as a naturalised species,
particularly in the south-east and Welsh Preliminary assessment
borders. It is likely that this species will continue to
Veteran chestnuts should be maintained for spread under climate change.
their dead-wood value. Where it does not currently occur, or is present
as only a few trees, it is probably best, if
Where it has been planted and forms dominant
practical, to try to keep this species out.
stands two approaches should be considered:
Controlling or removing it where it is
If it can be effectively managed as coppice established is likely to involve major felling.
there may be a case for maintaining the stand Gradual thinning out is unlikely to be effective
largely as chestnut since this is likely to since it may simply increase the regeneration
Page 7Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
of the species in the gaps created. Hence Pine regeneration in woods is likely to be
where it is already well-established and limited by its need for relatively open
regenerating, it may be less disruptive to conditions and some soil disturbance for
accept it as a future-natural new woodland seedlings to establish.
type. Hotter summers may favour pine spread on
Holm oak ecology in Britain should be a priority some soils where other species can currently
for future research. out-compete it.
Increased extreme events could provide more
Scots pine in northern England and on large scale disturbances that would favour pine
southern heaths regeneration.
Past distribution Increased fires might favour pine spread.
Scots pine was widespread across England
during the early Holocene period. There is Consequences of increased pine in woods in
debate as to whether these populations were England
the same as, or continuous with, those that In general pine is not likely to spread much in
spread in Scotland or whether there were most existing broadleaved woodland,
different origins and invasion routes. particularly if this is managed by minimum
Subsequently Scots pine declined in the pollen intervention, coppicing or as high forest using
record as broadleaved species spread. low intervention methods.
However, from comparisons with its behaviour Where it occurs as small stands or as a
elsewhere in Europe pine may have remained component of woods on acid soils the ground
a component of high altitude woodland in flora is not dissimilar to that under oak and
England, of woodland on dry acid sands and, birch stands on those soils.
probably as scattered trees, on acid bogs. Some pine-specific associated species do
Past management, particularly coppicing, occur in such stands from time to time,
would act against pine as it tends not to regrow increasing local diversity.
well after cutting. Oak and birch are able to establish in
There appears to be little, if any, direct association with pine, so it is unlikely that pure
evidence for survival of native pinewoods in pine stands will remain pure in the long-term
Britain into the historic period, except in the without regular disturbance.
Scottish Highlands. There is apparently a
medieval record for firs in the Lake District that Preliminary assessment
might refer to pine, but these do not seem to This is a different situation to those considered
have survived thereafter. previously in that it is re-introducing a species
The occasional occurrence of old native- south of where it currently survives as a native
looking pines in northern England and a species in Britain. The whole of England is
distinct saproxylic pine beetle assemblage in within its climatic range and some sites may
East Anglia and some Surrey heaths have become more suitable for Scots pine under
been interpreted as possible continuity of hotter summers.
scattered trees, if not woodland, through If we accept there were woods with a native
historic times in these areas (Roger Key pine component (even if not the dominant tree)
personal communication). on some soils and situations in the past then it
is not unreasonable to consider it as a
Future distribution component of new woodland in such areas
It has long been planted widely throughout (although not necessarily pure stands).
Britain, both within its native Scottish range Generally pine should not be introduced into
and elsewhere. Hence it is now almost ancient or other long-established woods where
ubiquitous in England. it does not occur, but there is no need to be
It spreads naturally very well from planted assiduous in cutting out natural regeneration if
stands, particularly on heathy soils. the soil and site appear appropriate.
Page 8Natural England Technical Information Note TIN053
Guidance on dealing with the changing distribution of
tree species
In northern England, if new pine stands are North American species most widely spread
being created there is a case for considering through the countryside are the dense shading
using a mixture of provenances from the native conifers which change the character of our
pinewoods (albeit there will be some risk to woods and wildlife significantly. The broad-
this from moving them south, against the leaved tree Robinia also has the potential to
climate change trend). spread more than it has to date under climate
In the south no particular provenance selection change projections.
is recommended from a nature conservation
point of view. Rhododendron, snowberry, laurel
These species spread to form dense thickets
Species this approach does not apply to! replacing existing understories, shading out
The following are examples only of species ground flora.
where the presumption should remain that,
Eucalypts
where nature conservation is important, they
should be removed if they occupy a significant These produce a very different type of woodland
area of the wood or are spreading. structure and composition (albeit there is very
limited data from UK conditions) and are
Norway spruce, European larch and silver fir taxonomically very different to British or
These species do occur on the continent but at continental species.
present the arguments against them are:
Further information
They are not particularly suited to the current Natural England Technical Information Notes are
or future climates in Britain. available to download from the Natural England
They do not appear to have naturalised website: www.naturalengland.org.uk . Other
regularly, despite several hundred years of notes on woodland include:
being planted in woods.
TIN001 - The historic environment and
They change the character of the woods
woodland management
significantly, through the nature of the shade
that they cast and their litter type. For information on other Natural England
publications contact the Natural England Enquiry
Turkey oak
Service on 0845 600 3078 or e-mail
This species is alternate host for the knopper enquiries@naturalengland.org.uk.
gall which attacks the acorns of native oaks.
Hence it should not be encouraged. Author
This note was developed by Keith Kirby, Natural
North American species
England.
The basic assumption behind this approach is
that our woods are part of a broader continental
continuum and hence species on the continent
might spread in time to them anyway. This does
not apply to North American species. In addition
References
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silviculture on former ancient, broadleaved woodland sites in south-east England. English Nature
Research Report, Peterborough.
GODWIN, H. 1975 The history of the British flora. Cambridge University Press, Cambridge.
GREEN T. 2005 Is there a case for the Celtic maple or the Scots plane? British Wildlife, 16, 184-188.
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Guidance on dealing with the changing distribution of
tree species
KENNEDY, C.E.J. and SOUTHWOOD, T.R.E. 1984. The number of species associated with British
trees - a re-analysis. Journal of Animal Ecology 53, 455-478.
LINHART Y.B. and WHELAN R.J. 1980. Woodland regeneration in relation to grazing and fencing in
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TAYLOR, N.W. 1995. The sycamore Acer pseudoplatanus in Britain - its natural history and value to
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alternation. Forestry, 65 (4), 417-433.
WESCHE, S., KIRBY, K.J. & GHAZOUL, J. 2006. Plant assemblages in British beech woodlands
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