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Sourcing native flora


A Flora locale guidance note

Flora locale  15/11/1999
 
© Flora locale (UK) 6 December 1999
This Technical note may be downloaded and distributed electronically or by simple photocopies but may not be published or sold for commercial gain. The guidance has been updated and presented more concisely in our document Go Native! Planting for biodiversity (guidelines).

To seek permission to publish this note, or extracts from it (electronically or otherwise) please contact info@floralocale.org.
1 Introduction

So you know what species you want to establish or grow on your site? But where should you source your plants and seed from?

Are you:
  • going to use plants of local native origin that reflect the local diversity of soil types and habitats in your area?
  • thinking of using plants that originate from another country (but are native species)?
  • concerned about using agricultural cultivars, such as registered and selected varieties of clovers, grasses and vetches?
  • going to use wildflowers that originate from seed collected in a meadow 400 miles from your site, or from one that is situated close by? 
  • Is the origin of your planting material important? Should you care?
Flora locale considers that you should care about how you source your plants, so as to:
  • ensure the genetic conservation of plant species that still grow in the wild (which may remain as very small and isolated populations)
  • ensure that your new plant community will provide the foundation for enhancing populations of other wild species, such as bees and butterflies
  • to maximise the chance of plant survival.
In overview of issues concerning the sourcing and use of native plants we have explained some of our concerns relating to the use of introduced forms and varieties of native species, and discussed why genetic variability and associated adaptation in native species is important. Below we again outline some of the issues, then outline our recommended approaches for sourcing of planting material for different types of schemes.
 

Some reasons to be cautious
 
Currently we do not know how important it is to use seed or plants of local native origin (i.e. whose parent plants grow in wild plant communities close to where the project site is situated). We do not fully know whether slight or major genetic variation within a particular species, is important either to its ability to survive and grow at a particular site, in relation to the wildlife which it supports or the type of management that might be applied.
 
There is plenty of anecdotal evidence that some plants of a variety or ecotype typical of a particular locality or geographic region can behave rather differently when transported to a different one. There may also be particular characters which relect local adaptation (especially to climate) that make the ecotype maladapted to areas beyond its natural range.
 
The period of dormancy, time of leaf fall and bud burst are characters of deciduous trees which may be particularly critical. A good example is provided by a variety which naturally grows in an area which is frost-free. If planted in an area where frosts occur, its rate of survival may be rather poor. Large-scale mortality has been associated with planting non-native varieties of native tree species for forestry. One of the worst cases has been reported from France where a Portuguese variety of Pinus pinaster was planted. Trees over 70,000 hectares died following severe frost.
 
Trees sourced from other countries may also be unable to respond to the different "switches" associated with daylength and daylight intensity - unseasonal leaf fall, or failure to drop leaves at all, has been reported by a number of people working in the horticulture and landscape trade.
 
Timing of bud burst and dormancy may also be maladapted to the place of planting, and can affect native species that are planted at different altitudes only a short distance away from their true native origin. This has been observed in Caledonian Pine (Pinus sylvestris ssp. scotica), which has one of the best-studied genomes of the native British trees. Distinctive Caledonian Pine ecotypes have been identified and mapped, and guidance on sourcing from appropriate localities has been produced by the Forestry Commission. Such detailed knowledge is not available for most other species but will gradually become available in the future.
 
Hawthorn (Crataegus monogyna) has been widely planted in new hedgerows all over the British countryside during the past 20 years, with the majority of plants coming from overseas (often Eastern or Central Europe). Recent research has shown that imported Continental hawthorn is more susceptible to disease, and is less thorny and environmentally robust in an upland Welsh environment, than a native Welsh variety.
 
Cultivated varieties of certain wildflowers, such as species grown as agricultural fodder varieties, have been widely sold into the landscape trade for use in nature conservation schemes in recent years. These varieties include species such as Sainfoin (Onobrychis vicifolia), Birds'-foot Trefoil (Lotus corniculatus), clovers (Trifolium spp), vetches (Vicia spp.) and Fodder Burnet (Sanguisorba minor ssp. muricata). The cultivars can be quite different in shape and form (and other vital characteristics) to native ones. Some varieties of Red Clover (Trifolium pratense), for example, are useless for certain bumble bees which normally feed on the wild strains. Others survive poorly in the long term, so are a waste of money if they are meant to be a long-term component of permanent grasslands re-created for wildlife conservation. Nevertheless, many fodder varieties have proved valuable for pollinators - and are useful when sown as pollen-nectar mixes and for green manures.
 
Sourcing strategies should also take into account the potential effect of introducing or translocating new forms of wild species into areas where there are already locally adapted forms. Again, little is known about how such introductions will impact upon perhaps small and fragmented populations of native species. Will local adaptive traits be swamped if large quantities of plants from another area, agricultural forms or even genetically modified varieties are planted close by?
 
In the UK, and in other countries (especially the United States) there is an ongoing debate about the relative importance of sourcing planting material from local areas. Our advice is largely based on the precautionary principle. It has some similarities with the strategy outlined in a North American research paper on this issue (Lesica & Allendor , 1999).

 

2 Sensitive localities
 
Sensitive localities are defined as localities which hold:
  • semi-natural plant communities
  • locally adapted forms of wild plants
  • fragmented and often isolated populations of native plants.

Examples of sensitive localities are: 

  • Sites designated as being important for their biodiversity value (e.g. Site of Special Scientific Interest)

Other land where ancient and well adapted native plant communities are found; in the UK these include:

  • ancient semi-natural woods and hedges
  • botanically rich grasslands, including meadows
  • semi-natural heath and heather moor
  • well-established wetlands, such as fens and bogs
  • other habitats identified as 'priority' habitats for UK Biodiversity*
  • the coastal fringe and islands.

* (UK Biodiversity Group. 1998. UK Biodiversity group Tranche 2 Action plans Volume II terrestrial and freshwater habitats.

 
2.1 Designated land
 

The following strategies should be used on or adjacent to designated land (in a British context this would be a Site of Special Scientific Interest): 

1. natural regeneration (this may include habitat management)
2. use of planting material that originates from the wildlife site
3. stock originating from a similar site that is close by (this strategy may be required for moorland rehabilitation).

The strategy chosen will depend upon individual circumstances.
 
As a general principle, seed and plants sourced from outside a designated site should not be introduced to the site. If there has been a problem of erosion or other damage, the priority must be to attend to the causes, and use physical or other means (e.g. reducing livestock densities) to address the problem prior to seeding or plug planting vegetation from other parts of the site. Habitat management, and management of activities that have caused the damage, should be the initial recourse, followed by seeding or planting where damage is severe.

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2.2 Grassland creation
 

Agri-environment schemes close to species rich grassland should refrain from using wildflower seed sourced from other localities. The following strategies are advised: 

1. Ideal strategy: commission wild seed collection from existing species-rich grassland; if necessary, bulk this up with the help of a local nursery; use only this seed to establish the new grassland
2. Less ideal strategy: Sow a grass sward at a low seeding rate, using commonly available agricultural grass varieties of "fine-grass" species; collect wildflower seed from existing species-rich grassland (bulk up in nursery if necessary); this seed can either be sown into patches of bare ground within the established sward, or might be grown as plug plants which can then be planted into the grassland.

Fodder varieties of wildflower species should be avoided in all schemes which have wildlife enhancement as at least one of their objectives and should never be purchased or substituted for the wild type.
 
Using agricultural varieties of grasses
 

Over recent centuries, the majority of commonly found grasses of agricultural value have been subject to considerable manipulation by selective breeding. Today, only a few seed merchants currently sell seed that is of known British native origin and local provenance. Because these grasses have been so widely used over a long period, the use of agricultural grass varieties is not considered to be as important an issue as the use of wildflower cultivars. However, Flora locale hopes that supplies of native origin grass seed will increase over succeeding years and emphasises that, wherever possible, seed of native origin and local provenance should be used where seeding is carried out within or close to sensitive localities.
 

Precautions should be undertaken when harvesting wild seed from a species-rich grassland, to ensure that the existing grassland is not damaged. For guidelines on harvesting seed from wildflower meadows see Crofts & Jefferson and the website section Seed Collection and Plant Propagation.
 
Strewing freshly cut hay from species-rich meadows is another approach that has been successfully used to enhance the botanical diversity of herb poor grassland, but partial destruction of the original (receiving) sward is usually necessary (e.g. using a graminicide or by stripping turf) to allow bare ground in which the seed can establish. Yellow Rattle (Rhinanthus minor) can also be sown into existing grassland to reduce grass growth and open the sward. Further details on this and other approaches is to be found in Crofts & Jefferson).

Enhancement tends to be more successful on sites with lower fertility and in swards that still contain a good variety of native grasses (and correspondingly more difficult on rye grass-clover swards which are highly fertile).
 
There have been circumstances when seeding is due to take place adjacent to a botanically important site, such as a coastal grassland SSSI, but when no local seed has been available. The most appropriate approach to dealing with this type of situation is to sow widely available agricultural varieties (not horticultural ones) of fine-leaved native grass species that reflect those found in other permanent grasslands in the area. 
 
Examples of fine-leaved native grass species for re-creating wildflower grasslands
Red Fescue (Festuca rubra) Crested Dog's-tail (Cynosurus cristatus)

Small Timothy (Phleum bertolonii) Common Bent (Agrostis capillaris)

Yellow Oat-grass (Trisetum flavescens) Sweet Vernal-grass (Anthoxanthum odoratum)
 
These species are suitable for dry grasslands and lowland meadows on a range of soil types.
 
Once this sward is established, it can be augmented with wildflower and native grass seed collected from native plant communities in the locality, ensuring that bare ground is first created into which the seed is then sown. Grazing will help the spread and establishment of wildflowers. White clover, or agricultural varieties of other clover species, should not be used.
 

Road verges and land associated with highways
 
Where land disturbance results from highways developments, such as construction of a new highway, plant sourcing should pay close attention to the characteristics of the surrounding vegetation. In general, topsoil should not be imported as this tends to be highly fertile, favours noxious weeds and the development of a plant community that is out of character.
 
Wherever possible, natural regeneration should be encouraged or seeding and planting should involve the collection of seed from the local area (this can be bulked up using the resources of a local or other specialist nursery). Highways schemes take a considerable number of years to proceed, so there should be ample time to undertake the specialist seed collections that are needed and this aspect of landscape design should be incorporated into the earliest stages of the scheme design.
 

Further detailed advice on roads is available in Scottish Government and Highways Agency publications.

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2.3 Heather and heathland restoration
 
Restoration of heather swards on degraded heath or moor may also benefit from seeding, but if the primary reason for deterioration is overgrazing, this must be addressed first. Lower stocking rates for livestock (about 1 sheep per ha in uplands) may be all that is needed to promote heather recovery, even on moorlands which have become grass-dominant in living memory. Sources of heather seed for heathland and moorland restoration should ideally be local and collected under specific contracts by mechanical seed harvesting, or by cutting heather stands containing seed heads, baling this up and then spreading it on donor sites. Heather seed collected in this way should be taken directly to the receiving site, as it will rapidly deteriorate unless it is professionally cleaned and put into cold storage. For lowland heaths, intense summer fires (usually arson attacks) and lack of grazing are two problems that should be addressed before heather seeding is undertaken.  Research by Meikle (1999) suggests some genetic variation in heather (Calluna vulgaris) populations related to geographical location.
 
2.4 Ancient hedgerows
 

Ancient hedgerows that contain six or more woody species, may represent fragments of the original wildwood which cloaked the British Isles before people cleared the land for agriculture. Their restoration should be carried out sensitively. Unfortunately, a significant amount of recent restoration has involved planting shrubs and trees of introduced origin, as well as species that haven't reflected the composition of the original hedge. As a result many hedgerows, which ought to provide a valuable historical record, have been altered for the first time in centuries.

The most desirable strategy for hedgerow restoration is to use trees and shrubs of native origin, preferably grown from seed sourced from local ancient woodlands, ancient hedgerows or scrub within the same local biogeographic region and seed zone (the seed zone, which is designated by the Forestry Commission, and the local biogeographic region will overlap but have different boundaries).
 
The species chosen should also reflect the existing mix of species that are present in the hedge.
 
A landowner could keep costs down by collecting the seed him/herself and growing it on a plot situated on the farm. Alternative, a local nursery could be contracted to carry out seed collection, should appropriate material be unavailable "off-the-shelf". Guidance on tree and shrub seed collection is available in the Forestry Commission  Practice Note on Using Local Stock for Planting Native Trees and Shrubs and in this website.
 
The degree of care taken over sourcing will need to closely reflect the needs of individual sites and circumstances, but the priority is not to obscure the historical character of the locality by imposing something that will be completely different and out of character. 

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2.5 Hedgerow restoration - general
 
Hedgerow restoration, including the planting of new hedgerows, should aim to plant a mixture of hedgerow shrubs appropriate to the local context. Once well established, to the extent that the new hedge is casting a reasonable degree of shade (probably after about six years), the reintroduction of hedgerow herbs can also be considered. These could also be grown from seed collected from local woods. Only plants that are very abundant in the locality should be used for this purpose.
 
Agricultural practices, such as herbicide spray drift, fertiliser spinning and heavy grazing will prevent the re-establishment of hedgerow ground flora. Ground flora plantings should not be carried out if any of these practices affect the hedgerow. 
 
2.6 Ancient woodlands
 
Trees and shrubs should not normally be planted in ancient semi-natural woodlands, where natural regeneration is the preferred approach for restoration. These are special places. Here, grants from the public sector are better directed towards deer fencing than planting and paying for the intensive management that planting requires. Rather too many ancient woodlands have been damaged by inappropriate planting schemes and are now full of regimented ranks of "weed-free" trees of unknown native origin (while naturally regenerated trees have been viewed as "weeds" and have been cut down from around the planted ones). This in turn poses future problems for collecting seed from trees in these woodlands, as it becomes increasingly difficult to identify which trees and shrubs are native to the site and reflect "wild" examples.
 
Leaving a substantial amount of dead wood on the ground, rather than the usual "tidy woodland" approach is particularly important for encouraging natural regeneration, especially in heavily deer-grazed woods where a tidy approach by woodland managers has created a dearth of dead wood. Fallen branches and the mass of tangled twigs associated with the crown and root plate of a dead tree, provide structures for bramble and other climbing plants, and good protection for young tree seedlings - away from browsing deer. Leaving dead wood around also restores important nutrients to the woodland soil, that can be used by seedlings and other young trees.
 
Ancient woodlands which have been severely degraded, and where there are rather few seed bearing trees and shrubs present, will require replanting. Under these circumstances trees and shrubs should be grown from seed selected from intact semi-natural ancient woodlands, native scrub or ancient hedgerows in the locality that are situated on similar soils and with similar drainage characteristics.
 
Information about how to identify whether an ancient woodland is ancient or not, plus the county and regional Ancient Woodland Inventories, is available from offices of the country nature conservation agency and may be available on line (e.g. from the Magic website). 

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2.7 Other semi-natural woodlands and new native woodlands 
 

The UK Forestry Standard (Forestry Commission, 1998) and associated Forestry Practice Guides nos. 1-8 (The Management of Semi-natural Woodlands) recommend using plants of local provenance, preferably from semi-natural parent trees (i.e. preferably grown from seed collected from trees and shrubs of native origin). The UK Woodland Assurance Scheme also seeks the use of seed of local (native) origin for restocking and planting semi-natural woodlands where this is available and considered appropriate. The Forestry Commission Practice Note Using Local Stock for Planting Native Trees and Shrubs provides further guidance on sourcing planting material for replanting semi-natural woodlands or for planting new native woods.


2.8 Coastal sites, islands and ecologically isolated localities 
 
There are many some examples of plant species which have varieties that are specially adapted or endemic to coastal situations and islands, so special care should be taken when introducing plants in these areas.
 
Ideally, the precautionary principle should apply, using a specialist to collect local seeds under contract to grow on and propagate/bulk up or sow directly on site. (Advice from a qualified native plant ecologist or local botanist should be sought in selecting the species to establish.)
 
Alternatively, a combination of natural regeneration and habitat management should be considered, where feasible.
 
There are also other isolated or characteristic localities, where ancient and well-established habitats, such as native grasslands, heath and woodland are found. The majority of these localities have been individually identified as local biogeographic regions or are Sites of Special Scientific Interest and include large areas such as the Chilterns (England), or smaller ones such as the Lizard (England) and Lleyn Peninsula (north Wales). The preferred sourcing strategy for these areas should be to use material of local native origin (or local provenance trees and shrubs where it is difficult to identify material of native origin).
 

3 Less sensitive localities 
 
Using natural regeneration should not be ruled out in these localities.
 
Wherever possible, material that is of local native origin or local provenance trees and shrubs should be used. The initial area of search should be the local biogeographic region, or the Forestry Commission Local Seed Zone. If material is unavailable, the area of search should be spread outwards until a source has been located.
 
Plants of Continental native origin may be more appropriate in some circumstances, e.g. where the nearest available source is a similar locality in France. An example might be a habitat creation scheme in Cornwall, where the nearest available source of plants is Brittany - an area which is biogeographically similar.
 
It is not necessary appropriate (and probably unrealistic) to always use locally sourced planting material for artificial sites, such as old waste tips, contaminated land or new landscapes in urban areas. This is because the soils are usually artificial, consisting of imported materials of varied origin. Native plants that are adapted to semi-natural habitats in the locality might be poorly adapted to the soil conditions found on artificial sites. However, plant survival will be a key issue and plant selection should take into account the site conditions, altitude and latitude. Birch (Betula spp.) used to plant a industrial spoil site in Scotland will probably have a poorer chance of surviving if sourced from southern England rather than if it were sourced from a more northern latitude!
 
The subject of adaptive forms of native plants for contaminated land restoration is an issue requiring more research -there may be a case for creating seed banks of and propagating plants that have naturally colonised such difficult sites to enable the more rapid restoration of other difficult sites. 

Research in the United States into strategies for using different native plant sources, suggests that the selective use of cultivars may be helpful when rehabilitating artificial sites, and that using a wider range of sources for seed and plants may give a landscaping scheme a better chance of succeeding (because there is more likely to be a wider range of adaptive traits in the species and varieties selected). In a GB context, the use of cultivated varieties of grasses (which are widely used in urban landscapes anyway) is acceptable, but prior knowledge about the growth and behaviour of the varieties should be used to select the right ones for the type of scheme and the soil conditions that are present. Aggressive tussocky species, for example, should be avoided if a wildflower landscape is to be established (and where herbaceous species are to be encouraged). It is recommended that wildflowers and trees of native origin and local provenance should always be used - cultivars of these plant groups are normally designed for amenity or agricultural purposes, not sites which have difficult soils.
 
Habitat creation on artificial sites must also take into account the proximity of other areas of surviving semi-natural vegetation. Wherever possible, sourcing should take advantage of these areas. For example, wildflower meadow creation in urban parks in the Oxford urban area could benefit from using seed from the vast native wildflower meadows that still exist on the outskirts of the City - meadows that are far more ancient than most of the City's historic buildings.

4 Locating plants and availability 
 
This issue is dealt with in more detail in the Flora locale Technical Notes "An overview of issues concerning the use and sourcing of native plants", "Types of native planting material currently available" and "Who can supply native plants?".
 
There is an increasing desire among scheme designers and funders to use plants of local native origin and local provenance, but supplies are still inadequate to meet the demand. Hopefully this situation will improve, especially if plant users continue to press nurseries to supply this type of planting material and if they are prepared to extend the planning period for their projects.
 
Current supplies could also go a bit further if project managers took slightly different approaches to the quantities of plants used in schemes. Many tree planting schemes carried out for landscaping and amenity purposes are "over-egged" - too many trees, based on an assumption of planting failure (often because the trees are bare-rooted stock lifted by Continental nurseries before the beginning of winter). It should be possible to plant fewer trees and shrubs, using younger plants. Similarly, wildflower seeding is often at relatively high seeding rates, using expensive wildflower seed. Lower rates for wildflower seeds are possible (@ 100-350g per acre) and, over a period of 5-10 years, can produce an attractive wildflower grassland. One recent chalk grassland creation scheme used all local seed, hand collected by a farmer and his friends from churchyards and field edges. This was sown at a rate of 3kg per hectare, with excellent results. Better attention to aftercare would also mean that plant survival rate could be substantially enhanced.
 

Applying Flora locale's guidance in this Technical note will, we appreciate, be difficult in the short term. However, there is now a sea change in attitude about the importance of paying attention to plant sources and hopefully the availability of appropriate planting material is set to increase in years to come.

Document date: 15 November 1999
Flora locale gratefully acknowledges financial support provided by English Nature, the World Wide Fund for Nature and TRANSCO which enabled the production of this document. 
 

 


Page last modified on Friday 22 of June, 2012 17:54:40 BST