Nicola Arndt und Matthias Pohl - Neobiota

In this north temperate climatic zone, without intervention, various types of woodland would cover the
majority of the land surface of the UK, except around exposed coasts, on the highest mountains and on
deep peats where there are edaphic or climatic limitations to tree growth. However, as might be
expected in a country with such a long history of settlement, the bulk of the vegetation that can now be
seen within the forest zone consists of replacement communities, except in the most remote and
inhospitable areas. In fact, between 90 and 98 % of the potential forest cover of the UK has been lost
and, even where surviving woodland is more ancient, it is often much affected by silviculture and
other anthropogenic influences. Elsewhere, away from settlements, industrial areas and communication
networks, agriculture has converted much of the original forest cover to arable land, pastures,
meadows and heath, with weed and wasteland communities in more disturbed places. Within the 16
forest mapping units that are represented in the country, 19 phytosociological associations of
woodland have been characterised by the UK National Vegetation Classification (RODWELL 1991 et
seq.), while there are over 150 replacement communities. On a local scale, the complexity of
landscape history within the climatic and geological frame means that the mosaics of these vegetation
types are often very intricate.
2 A predictive framework for new native woodlands
The scarcity of woodland in the UK has long been a concern, both because of the country’s lack of
self-sufficiency in timber but also, over the past two decades, because of a desire to increase the extent
of native broadleaf woodland for its amenity and biodiversity value. To provide some ecological basis
for sustainable planting, a cheap pocket guide “Creating New Native Woodlands” (RODWELL &
PATTERSON 1994) has been produced by the forest agency. This uses the framework of the European
Vegetation Map to provide a broad zoning of the country, gives lists of trees and shrubs appropriate
for planting in the climate and soils of these zones and provides design guidelines for developing
mosaics of such woodland types on a local scale. This approach, which is novel for the UK, has
proved very popular for planting new woodlands on farmland, around building developments, on
reclaimed derelict land and along motorways, and has brought the concept of predicting potential
vegetation before a wide audience of practitioners in landscape design and silviculture. Training
courses for such professionals on the use of the guide have helped disseminate the approach.
As an example of how the guidelines work, a user wishing to plant a woodland on podzols developed
from siliceous bedrocks and sands in the north-west of England would find themselves within the
European Vegetation Map unit F8 Atlantic-Subatlantic birch-oak forest (Figure 1). In the UK,
surviving stands of this woodland type are typically dominated by mixtures of Quercus petraea,
Q. robur, Betula pubescens and B. pendula with Ilex aquifolium and Sorbus aucuparia and these are
the recommended species for planting – a disappointingly brief list, perhaps, for someone with an eye
only for diversity, but an appropriately species-poor assemblage for such impoverished, acid soils. In
time, such woodland develops a field layer with shade-tolerant ericoid sub-shrubs, Deschampsia
flexuosa, Galium saxatile, Oxalis acetosella and ferns and to assist with targetting new woodlands of
this type on congenial sites, the guidelines also specify optimal precursor vegetation where an existing
flora with these species already offers some prospect of the development of the predicted woodland
field layer more quickly – in this case, these precursors are a variety of grassland and heath
communities dominated by sub-shrubs such as Calluna vulgaris, Erica cinerea and Vaccinium
myrtillus.
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