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The importance of plant and seed
sources:
A problem of definitions:
The right plant in the right
place:
Principles of good practice concerning introduced species:
Introduction:
Today, many schemes, across all the major land-based sectors, have among their objectives the creation or restoration of plant communities that have value for native wildlife.
Examples include: the creation of new native woods the restoration and/or replanting of existing woodlands (including ancient
semi natural ones) the planting of new hedgerows, and the restoration of old and ancient ones the creation of
"new" habitats on bare land following gravel extraction, opencast mining, waste disposal, arable farming, and major engineering works (e.g. flood
defence works in river valleys) the restoration of damaged landscapes, such as
pipeline tracks across moorland, as well as lowland heath and upland moors damaged by repeated fires, overgrazing and pollution the creation of new "naturalistic" parks and public open spaces in towns and the enhancement of
existing uniform and biologically impoverished urban landscapes the enhancement of botanically poor gang-mown grasslands on land owned by utility companies and other corporate bodies the enhancement of botanically poor agricultural
grassland, especially where there is an environmental imperative to reduce agrochemical inputs (e.g. in Nitrate Vulnerable Zones) the construction of new wetlands for nature conservation, flood
defence or for controlling pollution
("constructed wetlands").
At the very smallest scale, the establishment of native plant species in gardens, is also becoming increasingly popular. Even a small plot of native meadow wildflowers will quickly attract hoverflies, bumblebees and other welcome
beasties. Properly managed, wildflowers in gardens are not only as attractive as the usual cultivated ones, but are usually of much greater value for wildlife. More about gardening with wildlife in mind can be found on the Flora-for-Fauna
website.
Plants that are established in these schemes will provide the essential building blocks upon which new areas of biological diversity can evolve - from microbes and fungi networks that are associated with plant roots and soil, to leaf
and nectar feeding insects, birds, reptiles, amphibians and mammals. With pressure continuing on existing
wildlife habitats and species, and an increasing public desire to be put in touch with "the wild", this
up swelling "go
native" movement offers a chance to put something back. But habitat creation should not be seen as a substitute for the proper conservation of important habitats that still exist. However, if the "go native"
projects undertaken at a field or landscape scale are to make a real and significant contribution to enhancing local environments for wildlife, there are a range of issues which need to be addressed.
The importance of plant and seed sources.
The increasing interest in and public support for the restoration of native vegetation (including broadleaved woodlands, hedgerows, wildflower meadows, heaths and grasslands) has created a demand for plants and seed of native
wildflowers, grasses, trees and shrubs. For a number of reasons, this demand cannot yet be met by local growers and instead the majority of planting stock has been imported from other countries. In fact the majority of native trees
planted in the UK within the past 25 years have been sourced from overseas and do not represent the native genetic variability of trees found growing in the wild in the UK. In recent years an increasing amount of the wildflower seed used
has been of British native origin, but the use of imported continental material, agricultural and amenity varieties is still commonplace. Practically all the grass seed used in the UK is sourced from abroad. More detailed information on
plant and seed sources may be found in the section titled "Sources of native-origin
plants". The use of introduced or Tran located seed and plants may have a variety of consequences. These
include: potential for erosion of
existing genetic diversity represented in wild plants through hybridisation with the introduced ones differences in the characteristics, growth and
behaviour of non-native or non-local varieties (e.g. greater or lesser frost-tolerance,
varying ability to germinate in wet conditions, timing of bud burst and dormancy) may have consequences for associated fauna and the long-term survival of plants that are not adapted to local conditions extra costs are incurred if schemes
are unsuccessful (in some cases, introduced varieties perform less well and fail to survive) a habitat composed of "imported" plants is unlikely to represent (and may not resemble) native vegetation characteristic to the local
area (an issue of cultural as well as biodiversity concern) increased risk of introducing and spreading invasive introduced (exotic) species, including fungal and viral pathogens.
PlantLife - the
Wild plant Conservation Charity, was one of
the first organizations to highlight these issues in the report Seeds of Destruction
(Akeroyd, 1994). Since then has been an increasing appreciation that the origin of plants and seed is important. However, at present, there is a
dearth of scientific knowledge about the genetic variation and adaptive traits of our native plants, and whether small differences exhibited in a particular species, are important. We do know that there is adaptive variation among some
species, and that physical differences in the shape or size of a flower when it is selectively bred can make it useless for native insects which take nectar from the wild forms. A little research carried out into genetic variation among
native species growing in the UK, has also found that plants of the same species growing at different locations can be quite different in their appearance, growth and
behaviour. These variations have evolved over long periods and reflect
adaptation to local conditions, such as climate, soil chemistry and water. For example, distinctive forms of some wildflowers have evolved where species populations have been isolated for a long time, such as on the coastal fringe, on
islands and in local biogeography regions that are well separated from other similar ones. Differences have also been identified among tree species growing at different altitudes or latitudes. Armed with the little information we do
have, it is difficult to be certain about what the best approach to sourcing planting material should be for individual species and locations. For this reason, the approach proposed by Flora locale and by the UK Forestry Commission (the
only UK government agency to have, so far, attempted to have tackled this difficult subject) to sourcing planting material is based upon the precautionary principle - with emphasis on sourcing plants from the local area, wherever
possible. However, it is accepted that, given the dearth of current data, this strategy is not scientifically-based. More research into understanding genetic variation and adaptation in our native plants will help to refine this strategy
in the future.
A problem of definitions.
One of the major problems facing anyone wanting to "create" native plant communities and use appropriate planting material, is the wide range of definitions applied to describe different seed and plant sources. Definitions
for identical terms, such as "origin" and "provenance" are different, depending on whether you are talking to someone working in forestry, landscape or horticulture.
To overcome this, Flora locale has produced a
Specification for Native Plants.
The terms that Flora locale asks plant
specifiers and suppliers to use Native origin: planting material collected from parent plants whose wild origin has been documented and is known by the
supplier. An example might be Oxeye Daisy (Leucanthemum vulgare) grown as a wildflower crop from parent plants that have been grown from seed collected from an ancient wildflower meadow (i.e. a wild site that whose vegetation not been
planted). All wildflower seed, trees and shrubs that are used for ecological restoration should be of native origin. Trees and shrubs used to create new native woodlands or used for landscape planting in towns or along highways should
preferably be of native origin (see above). Local provenance: Seed or plants that can be traced back to a wild site, but the parent plants are of unknown origin, such as an oak tree that may have been planted in a native woodland. However
the parent plants appear native and well adapted to the site in which they grow. This term can also be used as a supplementary descriptive term to describe planting material of native origin that is destined for use in the same local area
as it was collected from. The place of native origin or native provenance should be stated (e.g. Plant of British native origin, or, Native origin: Berkshire, Plant of Hungarian native origin). The term "provenance" is otherwise
meaningless, as it means "the place that a seed or plant was collected from", which could be a plant nursery. To achieve a standardisation in the way the terms are used, plant collectors, growers, suppliers and users are
invited to adopt Flora locale's Code of Practice for collectors, growers and suppliers of native flora. This also requires the source to be identified at the point of supply in particular, the place of native origin should always be
given, or stated as "native origin not known").
The right plant in the right place.
Using the right combination of native plant species will create a framework which will promote the colonisation of a site by a diverse range of insects and other invertebrates, such as butterflies, ants and bumble bees. The native
plant community is, in effect, the essential building block for re-creating and rehabilitating biodiversity in damaged landscapes. However, no one should be deluded into thinking that a pristine and wildlife-rich habitat, such as a
stunning wildflower meadow, can be re-created overnight. If the objective of a scheme is to create some kind of coherent plant community, it is not only important to select the right combination of plants, but species which will actually
grow. Like plants commonly used in formal horticulture, British native plants include annuals, biennials, perennials, species which like lime-rich soil and those which do not, wetland plants which don't grow on droughty sands, and so on.
In the wild, these plants form distinctive associations which reflect the nature of the soil, the water regime, geographical location and influence of management (such as sheep grazing or mowing) or interference by people, animals and
other fauna. These plant associations are described in the British Plant Communities volumes (published by Cambridge University Press). A useful abbreviated synopsis is also published as British Plant Communities in Natural Associations
(Christopher Betts, 1997).Other useful references are:
Planting mixes based on the National Vegetation Classification system. (Authors: Joanna Francis & Graham Dixie, 1996. Published by H V Horticulture Ltd, The Street, Sutton Waldron, Blandford Forum Dorset DT11 8NZ) Creating New
Native woodlands. (Forestry Authority & Forestry Commission Bulletin 112. Authors: John Rodwell & Gordon Patterson. £9.95. ISBN 0 11 710320 9. Available from the Stationery Office) There are also two electronic decision support
systems currently under development (at October 1999):The Ecological Site Classification System (Forestry Commission) (currently this is focused on tree planting and selection) The Habitat Restoration System (Institute of Terrestrial
Ecology for the Ministry of Agriculture). Details on availability, hardware specifications and costs are not yet available. Understanding the natural range of native plants is very important when selecting species to establish -
both to ensure that the plants will survive and that the naturalness of remaining native plant communities in the locality is not deleteriously affected. Maps showing the national distribution of native plants (by 10 km square) can be
found in the Atlas of the British Flora (soon to be revised by as the Atlas 2000). More detailed distribution maps are also available for most of the English counties, published as individual county floras. Details of these publications
are available from the Botanical Society of the British Isles. Judgments about what is the right species to plant must take into account both the ecological and landscape context of an area, as well as the scheme objectives. In some
cases, this may lead to a decision to plant a native species outside its natural range but not where nature conservation is the primary objective. Some native species have already been extensively planted outside their natural range and
in the wider countryside, where they are now considered to form important components of the landscape. Beech is such an example. In contrast most native wildflowers have discrete natural ranges and their distribution has, historically,
not been extensively tampered with.
Bird Cherry Prunus padus is a very attractive small native tree worthy of planting in urban areas, but its natural distribution in Britain is patchy. It should not be planted in ancient woodlands and hedgerows where it had never naturally
occurred in recent history (and where it could be potentially invasive and eventually distort the balance of indigenous tree and shrub species). This is an example of a native species where planting outside its natural range would be
acceptable in certain "controllable" circumstances, but could pose problems to existing wild plant communities in others. The establishment of native species outside their natural range also has implications for environmental
monitoring. Mapping and monitoring the distribution of native plants helps us to assess the state of the environment. Native plant introductions (putting native plants in areas where they have never occurred before) need to be recorded,
so that background changes to plant distributions are not obscured. This is particularly important in the context of identifying changes in British vegetation that may be associated with global climate change. Any introductions of this
sort, if they must take place, should be notified to the Botanical Recorder for the area. Details of Vice-county Recorders is available from the Botanical Society of the British Isles.
Establishing native plants, in the garden or on a larger landscape scale, can be challenging, but requires good knowledge on the ecological requirements of the plants, the place and context in which they are to be established, and the
future management that will be necessary to ensure their future survival. Lack of such knowledge can lead to disappointing results, wasted effort and money, and may prejudice opinion against using wildflowers and other native species
again.
For these reasons, good advice on what native species are appropriate for the planting site, should be obtained before embarking on a major scheme. This knowledge, is usually available locally either on a professional basis (e.g. from
a professional ecologist with botanical skills) or via amateur botanists who belong to the Botanical Society of the British Isles. It is also available from nurseries that specialise in collecting and propagating seed of native species.
Some of these also have expertise in site preparation and planting.
If you are not a plant ecologist, do not expect to learn the ecology of native plants overnight by reading a book! Expert advice is especially important at the earliest stage of designing large landscaping projects which involve
the selection and use of native species. For landscaping schemes which are predominantly using native plants, and which have as their principal purpose the creation of vegetation that is going to be of some wildlife value, the science and
practice of ecology is fundamental to scheme objectives, approaches and design.
5 Environmental responsibility and introduced species Introduced "exotic" species have an important role in enhancing the urban environment, parks and
gardens. But there is a scant awareness about the risks posed to our native
biodiversity from some introductions. Apart from habitat destruction by man, the spread of invasive introduced species now poses probably the single greatest threat to global biodiversity.
In the UK, measures now being taken to eradicate invasive plants are proving costly. At the same time, the globalisation of trade in horticulture, forestry and agriculture, means that many other wild species are piggybacking on
otherwise benign imports of trees, garden and crop plants. Some of these new invaders are pests that threaten agriculture, horticulture and our native
wildlife. One extreme example is the hybrid Phytopthera disease (the progeny of two
introduced species) which, by the beginning of 1999, had already destroyed around 10% of wild alder trees in southern England, and threatens to do to our alders what Dutch elm disease did to our native elms. Horticulture, landscaping and
habitat creation are potent sources of invasive exotic plant species.
Examples include:
Gaultheria shallon (invading Dorset heath land) New Zealand swamp stonecrop Crassula helmsii (which is effectively destroying wetland plant communities of international importance in the New Forest) exotic dogwoods (invading Irish bogs
having been planted on highway verges) New Zealand flatworm (which is gobbling up our native earthworms on an advancing front). Specific vectors of invasion
include: landscape gardening: planting invasive species in landscape schemes
(which then "leapfrog" into the wild) landscape gardening and well meaning members of the general public (e.g. angling clubs): the introduction and planting of aquatic plants of non-native species or introduced origin, into
ponds, gravel pits and freshwaters outside gardens (i.e. in the wider countryside) horticultural trade: the incidental establishment of exotic species (e.g. via transfer of seed, spores or plant fragments) which piggyback on grass seed,
in compost, or hitch a ride with aquatic plants similar piggybacking in compost or soil in plant pots or around plant roots. Flora locale wishes to encourage a responsible approach among professionals and land managers responsible for
specifying and using plants at the field and landscape scale.
The following principles of good practice are proposed concerning introduced species:
Avoid planting any species which is known to be invasive, such as Gaultheria, especially where the plantings are located close to habitats likely to be at risk stick to planting native species, of appropriate native origin, in the
wider countryside (including landscaped road verges on the edges or outside of towns)
Always assess the potential environmental impact of using non-native plants in large landscaping schemes, incorporating risk assessment procedures for the plant species and varieties themselves, as well as for the scheme in general
never introduce aquatic plants into new ponds or other water features (except in gardens) unless you know they are (a) native species and (b) of native origin (and never plant anything, even in garden ponds, that is already an infamous
invader). © Flora locale (UK) 10 February 2001.
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