The nature conservation value of scrub in Britain
This report represents a synthesis of the existing knowledge of scrub ecology and conservation, and identifies priorities for future conservation and research. This information has been accessed through published and unpublished literature, questionnaires, an expert workshop, and through consultation with national and international experts.
Rationale and approach
- Scrub has received little attention from nature
conservationists, resulting in insufficient knowledge of the
distribution, ecology, management and conservation status of scrub
in Britain. This information is needed to identify, conserve and
enhance valuable scrub.
- This report represents a synthesis of the existing knowledge of
scrub ecology and conservation, and identifies priorities for
future conservation and research. This information has been
accessed through published and unpublished literature,
questionnaires, an expert workshop, and through consultation with
national and international experts.
Definition and classification
- For the purposes of this report, scrub includes all stages from
scattered bushes to closed canopy vegetation, dominated by locally
native or non-native shrubs and tree saplings, usually less than 5m
tall, occasionally with a few scattered trees. This includes carr,
scrub in the uplands and lowlands (including wood edge habitats),
montane scrub and coastal scrub. The definition excludes dwarf
shrub heaths, planted stands of young trees and coppice stump
regrowth less than 5m high.
- Most scrub in Britain is seral, forming a stage in the
transition from open herbaceous vegetation to woodland. In certain
situations, scrub can be considered a climax vegetation type, for
example where altitude, exposure or edaphic factors limit tree
growth. Such communities can be found in the alpine and sub-alpine
zones, on exposed coasts and on skeletal soils.
- For seral scrub, problems of definition occur when separating
scrub from herbaceous and woodland vegetation. For species which
have ranges above the scale of an individual scrub stand, the
intimate mix of scrub with woodland or herbaceous communities is an
important habitat requirement.
- Widely used classifications of scrub types depend on
floristics, the identity of dominant woody species and soil
characteristics. However, for describing the conservation value of
scrub types for associated organisms, especially birds and
invertebrates, classifications which take account of both
horizontal and vertical structural complexity are
- The National Vegetation Classification describes five scrub
types, although scrubby vegetation forms an important component of
many other grassland, heath, mire woodland and coastal NVC
- In Britain, scrub vegetation comprises a significant component
of six priority habitats types in the EU Habitats Directive, namely
dune juniper thickets (Juniperus spp.), semi-natural dry
grasslands and scrubland facies on calcareous substrates
(Festuco-Brometalia) (important orchid sites), limestone pavements,
Caledonian forest, bog woodland and residual alluvial forests
- Scrub vegetation comprises an important component of 11
Priority Habitats in the UK Biodiversity Action Plan, and a minor
component of several others.
Distribution and conservation value
- The available information on the distribution and abundance of
scrub communities in Britain is inadequate.
- Best estimates (from the ITE [CEH] Countryside Survey 1990) are
that there is 900 ±200 km2 ( 90,000 ±20,000 ha) of scrub
in Britain. On a country basis this breaks down into: England 600
±100 km2; Scotland 200 ±50 km2; Wales 100 ±50
- Scrub occurs widely within SSSIs but has rarely been taken into
account when designating them. Hence it is not known to what extent
the distribution and abundance of particular scrub types within
SSSIs is representative.
- Scrub is generally valued by managers of designated sites for
its contribution to biodiversity.
- In England and Wales scrub is generally (with the exception of
juniper) valued primarily for the species it supports rather than
in its own right. In Scotland scrub (mainly upland and montane) is
more often valued for its own intrinsic value.
- Scrub is known to be an important habitat for a wide range of
higher plants, herbivorous insects and birds, including Red Data
Book and BAP1 species.
- Little is known about the value of scrub for lower plants,
non-herbivorous invertebrates, reptiles and amphibians, and mammals
although scrub is likely to be equally important for these
- Most British scrub communities are well represented elsewhere
in Europe. However, hawthorn scrub is particularly characteristic
of the English lowlands and of marginal uplands in England and
Wales, while Scottish montane dwarf willow communities differ in
detail from their Scandinavian counterparts, perhaps reflecting
- Scrub in Britain is almost entirely a product of man's
activities. In primeval landscapes, scrub would have occurred in at
least five situations and local examples can still be found. These
situations are: in primary successions such as dunes, on exposed
coasts, as high altitude montane scrub, as ecotones between
woodland and open habitats, as natural regeneration within treefall
- The majority of scrub results from secondary successions. In
the lowlands, the breakdown of traditional grazing and cutting
regimes on marginal land has been a major stimulant for scrub
development. Large-scale expansion of scrub may occur in the
uplands as a result of abandonment of hill farms and reduction of
- The mechanisms driving the successional development of scrub
are poorly understood. A range of mechanisms may operate
simultaneously. Seed dispersal may be a critical factor in the rate
of scrub development and in the structural mosaics that develop.
Most scrub species are dispersed by birds and factors such as
proximity to seed sources, availability of perches and quality of
the receptor site for dispersers may be important.
- Successional development of scrub involves increases in soil
nutrients, organic matter, shifts in the composition of the ground
flora and ultimately reduction in the seed bank. These changes are
accompanied by continuous development in the structure of the scrub
as a result of canopy-closure and increasing height of the woody
vegetation. Structural development of much upland birch and pine
scrub appears to be less complex than in much lowland
- For many taxa, shrub species composition is less important than
microclimate, microhabitat structure or macrohabitat structure.
However, examples of apparent dependencies on particular species
are to be found among the lower plants and among phytophagous
insects. The majority of phytophagous insects are specific to plant
family and a substantial number are specific to plant
- Many invertebrates and birds are associated with specific
vegetation structures. This results in large ongoing changes in
insect and bird communities as a result of the massive structural
changes that accompany scrub development in succession.
- Scrub often exists as a mosaic with grassland and other open
vegetation. Spatial patchiness is an extremely important habitat
feature for many plants and animals. In the case of invertebrates,
fine-scale mosaics of structure and plant composition provide a
diversity of niches and a variety of food and shelter. Edges are
particularly important and intimate mixtures of grass, scrub and
woodland may be advantageous to many insects. Similar structural
patchiness can result in very rich bird communities. The
maintenance of such mosaics is a difficult management
- There is often insufficient clarity in setting objectives for
scrub management due to imprecise definitions of its
- Scrub is often felt to be both beneficial and a nuisance on the
same site, especially in the English lowlands where invasion of
species-rich grassland is a very common problem. However, the
proportion of scrub which is considered to be a nuisance is
generally small (<25%). Juniper and hazel scrub are always
- Much management of scrub in lowland England aims to develop and
maintain mosaics of scrub and grassland, which are believed to
favour the widest range of flora and fauna. Scrub is generally less
welcome on wet habitats in the lowlands where it may adversely
affect site hydrology. It is also often unwelcome in coastal areas
where it invades maritime grasslands and dwarf shrub heath of
international importance. Sea buckthorn, although having
appreciable conservation value in its own right, is generally
regarded as a pest species in sand dune systems.
- Scrub is generally reviled by archaeologists and geologists who
consider it a nuisance where it damages or obscures features of
- Scrub is rarely considered to be a nuisance in the uplands and
in Scotland there is a major programme for the protection and
enhancement of montane scrub communities.
- A very wide range of techniques is used for scrub management
and control, with very varying success. These techniques are mostly
based on cutting with or without stump treatment followed by
grazing or mowing. Practitioners urgently seek improved information
on which techniques are appropriate where and when and how they
should be carried out.
- Rhododendron ponticum is by far the most serious
invading exotic scrub species throughout Britain accounting for 44%
of all cases mentioned by survey correspondents. Very large amounts
of money are spent annually on Rhododendron control and eradication
- Clearance of scrub is widely funded in lowland England, where
scrub is widespread and frequently encroaches onto habitats
perceived to be more valuable. In upland England and Wales, scrub
is less common, and grants are available for both conservation
management and clearance. Scotland contains a low proportion of the
British scrub resource, but many of the uncommon habitat types of
high conservation value. As a consequence, only management to
conserve and enhance scrub is funded.
- None of the schemes reviewed differentiate between scrub of
high conservation value and other types of less valuable scrub when
- Neither Countryside Stewardship nor Environmentally Sensitive
Area schemes in England fund annual management to conserve or
- Land management grants to promote conservation and enhancement
of wet scrub (willow and alder carr) are available in only a few
regions of Britain.
- The nature conservation value of scrub is generally related to
its structure, including elements of both vertical canopy structure
and horizontal spatial structure in relation to other habitats. The
National Vegetation Classification, being based on floristic
inventory of homogenous stands, is therefore inadequate for
ascribing conservation value to scrub stands.
- There is a need for a structural classification of scrub that
is ecologically meaningful in terms of the requirements of
scrub-associated organisms, especially invertebrates and birds.
This classification must take account of spatial structure (mosaics
/ patchiness), scrub height and foliage profiles.
- In order to assess the absolute and relative importance of
scrub to nature conservation, whether regionally, nationally or
within Europe, there is a need for better information on the
distribution and extent of the major scrub types.
- Treatment of scrub within land cover surveys adopted by various
agencies varies considerably. Much information on national
distributions is potentially available within the ITE Countryside
Survey 1990 and Countryside Survey 2000 datasets but it is
currently in aggregated form under the main category 'Shrub'.
Dis-aggregation of these data would provide information at the
required level of detail.
- Certain rare scrub types (e.g. juniper scrub) or scrub composed
of rare shrub species (e.g. Salix lanata) have Habitat or
Species Action Plans within the UK Biodiversity Action Plan. No
changes to the definitions of broad or priority habitats are
considered necessary. However, the conservation value of scrub as a
structural component of many priority habitats needs to be fully
acknowledged in relevant Habitat Action Plans.
- An assessment is needed of the extent to which scrub within
SACs and SSSIs is representative of the wider resource and to
decide whether further designations are required to cover
under-represented scrub communities.
- Better information is needed on the status and management of
scrub within existing SSSIs, including occurrence of scrub types,
structural characteristics, associated species, conservation
importance within the SSSI and management objectives.
- An assessment is needed of the ecological contexts in which
scrub should form a criterion for SSSI designation. In addition,
citations for existing SSSIs and definitions of 'favourable
condition' may need to be changed to take account of the nature
conservation value of scrub.
- Research is needed to determine for which species and under
what circumstances scrub is a primary (or sole) habitat and when
and where it is of secondary importance.
- Characterisation of the unique attributes of British scrub
types in relation to those of mainland Europe is essential in order
to set conservation priorities within the UK. A meeting of key
European specialists could provide a starting point for a European
network on managing scrub vegetation for nature conservation.
- This review has identified the importance of mosaics of
vegetation, of which scrub is an integral part, for several taxa.
There is a need for research that identifies the optimum mosaic
structures for ground flora, invertebrates and birds. This work
needs to take account of the different scale requirements of these
taxa and should take account of the importance of edges and glades
- The processes of scrub establishment and the development of
patchiness within scrub are poorly understood. In particular, there
is a need to examine more closely the role of birds in seed
dispersal and how their behaviour influences the distribution and
spatial structure of scrub.
- A landscape approach to the importance of scrub for
conservation needs to be developed. This could have two main
components. First, an assessment of how the proximity of other
habitats, especially woodland and grassland, affects the plant and
animal communities found within scrub. Second, there is a need to
determine the contribution that scrub makes to biodiversity within
different landscape types relative to other habitats. The latter
work would help to identify the extent to which species are
dependent on scrub compared with other habitats and, therefore,
clarify the complementarity of scrub and other habitats.
- Research is needed on the successional dynamics of animal
communities (especially invertebrates, birds and small mammals)
within developing scrub. Such research should seek to identify
which are the richest stages of successional development, both in
terms of species richness and the presence of species of particular
conservation interest. These data would be valuable in helping to
underpin management policies that sought to maintain rich
communities of animals within scrub habitats.
- Carr has been remarkably little researched, especially
concerning its animal communities and how these are influenced by
factors such as successional stage and wetness. Further research in
this area seems highly desirable in view of the current
conservation interest in riparian woodland.
- Very little is known about the mycorrhizal associations of
scrub species and indeed, how these might benefit the rare
communities. Manipulation may enhance the success of establishment
or restoration of these communities, especially when soil
conditions are not optimal.
- Carefully controlled experimental research is needed to
determine the effectiveness of differing procedures for scrub
management, including procedures for maintaining scrub as well as
controlling it. This should take account of existing guidelines and
the considerable amount of information contained within the
responses to the questionnaire carried out as part of the current
- In the context of scrub control, there is a need to identify
whether critical thresholds of scrub development exist, beyond
which scrub clearance is ineffective as a means of restoring
habitats such as lowland calcareous grassland or fen.
- Research is especially needed on appropriate management
techniques for maintaining patchiness and mosaics. Rotational
large-scale cutting of scrub is unlikely to be adequate for
maintaining complex vegetation mosaics and approaches that adopt
grazing or combinations of grazing and selective cutting are likely
to be more successful.
- A scrub management handbook should be developed outlining best
practice for managing scrub, especially means of encouraging
sustainable mosaics of scrub and other habitats.
Dissemination and Education
- A major constraint on the conservation of scrub and its
associated species is the widely-held opinion that scrub is of low
conservation value and primarily a threat to other more valuable
habitats. Methods of addressing this problem of perception need to
- In particular, there is currently insufficient guidance
concerning situations where scrub is valuable and in which contexts
other conservation priorities take precedence. This problem is
exacerbated by the linkages between the conservation value of scrub
and its intimate association with other communities in habitat
- It would be highly desirable to establish a network of scrub
demonstration sites where different approaches to difficult scrub
management issues can be viewed and discussed with site
- In most situations, scrub is primarily considered as a threat
to other habitats, and capital payments allocated for clearance.
Funding for agri-environment schemes needs to take account of both
the efficacy of scrub clearance for restoring species-rich
herbaceous communities such as chalk grassland, and the intrinsic
nature conservation value of scrub or habitat mosaics including
- The introduction of annual management payments to conserve and
enhance scrub of high conservation value in England (as opposed to
one-off capital payments for clearance) would benefit scrub
conservation, and bring the English agri-environment schemes into
line with those in Wales and Scotland.
- Little attention is paid to the roles of landscape processes
when funding scrub management, despite the likely impact of the
surrounding landscape on the value of individual habitat patches. A
consideration of the large-scale spatial processes should be taken
into account when allocating funding for scrub management. This
approach relies on scrub of high conservation value being
identified in funding applications, something that is currently not
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- Conservation of seral scrub can only be achieved on a large
spatial scale, allowing management producing mosaics of scrub at
different successional stages.
- Wherever appropriate, scrub should be encouraged as part of
natural vegetation dynamics. For example, in the Scottish Highlands
there may be increasing opportunities to regenerate natural
woodland cover in which scrub is present not just in the initial
establishment phase but also in the longer term as a natural
component of the forest dynamics following disturbance by windblow
- A more positive approach to scrub habitats is required in the
uplands of England and Wales to match that adopted in Scotland. For
example, it might be interesting to consider how treeline scrub
communities might be enhanced in Snowdonia and the Lake District;
how scrub communities might play an important role in 'wild-wood'
developed on former conifer forest sites; how upland hawthorn scrub
might be regenerated and extended under agri-environment schemes;
how willow scrub might be used to enhance and link wet woodland
- Landscape policies that promote the large-scale expansion of
scrub on lowland flood plains would contribute significantly to the
conservation of residual alluvial forest (a priority habitat in the
Habitats Directive) and delivery of the Habitat Action Plan for wet
- Scrub and associated wet woodland communities frequently
develop on abandoned mineral extraction sites. Promoting the nature
conservation value of such sites amongst mineral planning officers
would provide opportunities for expansion of these habitats and
their appropriate management.
- Within the context of agricultural land, abandonment may
provide opportunities for the creation of scrub habitats. Issues of
negative perceptions of the value of scrub amongst landowners need
to be addressed.
- The use of scrub buffer strips adjacent to new farm woodlands
would contribute significantly to the nature conservation value of
- The nature conservation value of scrub, and of mosaics of
scrub, woodland and herbaceous communities, needs to be recognised
in the planning of new lowland woods and national forests.
Download in sections:
- Download Approach (PDF, 123 kb)
- Download Definition and classification (PDF,
- Download Distribution and conservation value
(PDF, 332 kb)
- Download Figures for Chapter 3 (PDF, 640
- Download Ecology (PDF, 400 kb)
- Download Management (PDF, 300 kb)
- Download Recommendations (PDF, 200
- Download References (PDF, 190
- Download 3.1 Coastal, lowland grassland and
heathland NCR sites (PDF, 120 kb)
- Download 3.2 Examples of SACs with important
scrub communities (PDF, 160 kb)
- Download 5.1 Countryside Stewardship management
prescriptions (PDF, 150 kb)
- Download 5.2 Environmentally Sensitive Area
management prescriptions (PDF, 200 kb)
- Download 5.3 Questionnaire responses on
techniques for scrub management (PDF, 220 kb)
- Download 5.4 Questionnaire responses on
objectives for scrub management (PDF, 215 kb)
- Download 5.5 Questionnaire responses on success
of scrub management (PDF, 220 kb)
- Download 5.6 Questionnaire for land-managers
and 6.1 Appendix Questionnaire for project officers and
advisors (PDF, 220 kb)
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ISSN 0963 8091
Please cite as: Mortimer, S.R., Turner, A.J., Brown, V.K., Fuller, R.J., Good, J.E.G., Bell, S.A. Stevens, P.A., Norris, D., Bayfield, N. and Ward, L.K., (2000), The nature conservation value of scrub in Britain, August 2000, JNCC Report 308, 191 pages, ISSN 0963 8091