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Dr Andy Scobie,
Project Officer

Cairngorms Rare Plants Project
Scottish Natural Heritage,
Achantoul, Aviemore,
Inverness-shire,
PH22 1QD

Tel: +44 (0) 1479 810477
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The species
Twinflower

Twinflower image panel

Description and ecology:

This delicate little dwarf shrub of pinewoods in the northeast of Scotland has prostrate shoots that creep along the forest floor and over the top of fallen trees, old tree stumps and mossy boulders. Each shoot, which can grow up to 50 cm in a year, produces numerous side shoots which in turn produce side shoots of their own. Over time, this process leads to the formation of large clonal patches characteristic of the species. The small oval leaves are evergreen and occur in opposite pairs along the reddish brown stems and can be reliably identified in the field at any time of year.

The tiny flowering spikes (up to 8 cm tall) are very distinctive, each bearing a pair of white/pink bell-shaped flowers (only 5-10 mm long), hence the name ‘twin-flower’. A striking carpet of flowers can be produced under favourable light conditions but flowering is often poor or completely absent when the plant is growing in heavy shade. The main flowering period for Twinflower extends from mid-June to late July, with the occasional late flower appearing until the end of September.

The flowers are pollinated by small flies, including muscid flies, empid flies and hoverflies, and occasionally by small halictid bees and bumblebees, which forage in the flowers for nectar and pollen. Each flower has the potential to produce just a single seed which ripens in August. The seed is partially enclosed by two bracts with sticky viscid hairs, and together these form the fruit which is adapted for long-distance animal dispersal, sticking to the fur or feathers of passing mammals or birds. Fruiting is infrequent in Scotland with the majority of patches producing little or no seed each year.

Low seed production in Scotland is the result of isolation of Twinflower patches consisting of single clonal individuals combined with the highly self-incompatible breeding system (i.e. Twinflower is almost but not completely self-sterile). Distances between remaining patches are typically very large, often hundreds of metres to several kilometres, and too great for pollinating insects to travel frequently between them, hence cross-pollination and seed production rarely occurs. High levels of natural seed production only occur where a number of compatible clones are situated within close proximity to one another, enabling insects visiting the flowers to transport pollen between them.

Recent research has demonstrated that experimental cross-pollination between neighbouring Twinflower patches (compatible clones) can restore seed production. These findings suggest that restoration of seed production in Twinflower could be achieved by transplanting carefully selected compatible plants within close proximity of existing isolated patches, or by creating new patches consisting of a number of compatible clones. Experimental trials are now required to investigate the potential to utilise translocation as a tool for the recovery of Twinflower in Scotland.

Habitat:

Twinflower typically occurs in the remnants of ancient Scots Pine (Pinus sylvestris) woodland and old pine plantations in the northeast of Scotland. In the latter situation it is often associated with the edges of forest tracks, extraction routes and clearings where light conditions are more favourable. Twinflower also occurs in completely open heathland (former sites of Scots Pine woodland), where it is strongly associated with north facing slopes, and occasionally in Juniper (Juniperus communis) scrub and Birch (Betula spp.) woodland.

Typical associates include: Blaeberry (Vaccinium myrtillus), Cowberry (Vaccinium vitis-idaea) and Heather (Calluna vulgaris), Wavy Hair-grass (Deschampsia flexuosa), Common Cow-wheat (Melampyrum pratense), Wood Sorrel (Oxalis acetosella), Tormentil (Potentilla erecta), Heath Bedstraw (Galium saxatile), Creeping Lady’s-tresses (Goodyera repens), Hard Fern (Blechnum spicant) and a thick carpet of pleurocarpous mosses (including: Hylocomium splendens, Pleurozium shreberi and Ptilium crista-castrensis).

The level of shade, both from the woodland canopy and sub-shrubs in the field layer, appears critical to vegetative spread and flowering of Twinflower, with the best patches occurring under the shade of a moderate Scots Pine canopy. Under heavy shade, the density of Twinflower shoots is greatly reduced and flowering is typically absent.

Distribution and status:

Twinflower has undergone a considerable decline in the UK, being lost from 44% of pre-1970’s records, and is now almost entirely confined to the northeast of Scotland.

Follow the links below to view a UK distribution map:
BSBI UK Distribution Map
NBN UK Distribution Map

The Cairngorms National Park is the UK stronghold where the species occurs locally in the pinewoods of Strathspey and Deeside, with outlying populations near Strathdon and on the rocky slopes of Glen Doll.

View the CNP distribution map here:
CNP Distribution Map ( PDF File )

Remaining patches are typically highly isolated from one another, often with several kilometres between them.

Twinflower has been identified as a conservation priority in the UK Biodiversity Action Plan and Cairngorms Local Biodiversity Action Plan and is included on the Scottish Biodiversity List.

Reason for decline and current threats:

1) The loss and fragmentation of native pinewoods.

Following centuries of exploitation for timber and widespread heavy grazing by deer and domestic livestock, the natural pine forests that once covered much of northern Scotland have been reduced to a few isolated and degraded fragments. This is clearly bad news for specialist pinewood plants like Twinflower.

2) Unsuitable woodland and heathland management practices.

Creation of dense plantations with uniform structure.
The replanting of felled native pinewoods with extensive areas of uniform closely spaced trees, or the encouragement of dense natural tree regeneration, with a heavily shading canopy suppressing the growth of understory plants below, including Twinflower.

Heather burning.
Twinflower is ill adapted to cope with heather burning, a management practice used extensively in the highlands of Scotland to create young fresh heather growth for red grouse, deer and domestic livestock and to encourage regeneration of tree seedlings. Twinflower is shallow rooted with no underground rhizomes from which to regenerate after fire and, since seed production is frequently very low, it cannot readily disperse back into burnt areas.

Inappropriate grazing levels.
The heavy grazing of pinewoods and heathlands by deer and domestic livestock leading to the ‘grazing out’ of species such as Twinflower and other pinewood herbs. Equally the under grazing of open pinewoods and heathlands can lead to tall and dense growth of sub-shrubs, in particular heather (Calluna vulgaris), which can shade out Twinflower.

Large scale clear-felling.
The change in common forestry practice from small-scale selective fells towards large-scale clear fells, leading to dramatic changes to the woodland structure and light environment following felling.

3) Reproductive isolation of single clones leading to low or zero seed production in many Scottish populations.

Although Twinflower can persist and spread locally by vegetative reproduction, and in some cases clones may persist in one place for hundreds of years, the production of seed is essential for recruitment of new genetic individuals into existing populations and long distance dispersal into new areas of suitable habitat. Without seed, isolated patches remain vulnerable to extinction and long-term prospects for recovery are severely limited.

Action for Twinflower in the Cairngorms National Park:

1) Increased recording and monitoring of Twinflower populations in the Park.

The location of all known Twinflower patches will be established, increased recording of the species will be encouraged, and searches conducted at historical sites and in areas of suitable habitat. Accurate GPS location data and basic monitoring data will be collected at all sites. This data will be used to inform land managers of the presence of Twinflower patches on their land and provide a baseline against which to measure future change.

2) Surveys of key sites to establish conservation issues and identify appropriate action.

Detailed surveys will be undertaken of Twinflower patches at key sites in the Cairngorms National Park to assess population health (eg. vegetative spread, flowering, fruit set and genetic diversity), habitat conditions and current and historical site management.

3) Implementation of conservation action.

Information from these surveys will be utilised to advise land managers on actions to promote the persistence and spread of twinflower. Experimental management trials with appropriate long-term monitoring will be set up to test the effectiveness of various management approaches and techniques and these will include:

Targeted habitat management

  • Management of ground-layer vegetation within proximity of existing twinflower patches to create open habitat to promote vegetative spread and flowering.
  • Localised canopy thinning/re-structuring to increase light levels within proximity of existing twinflower patches.
  • Creation of conservation zones for twinflower within commercially managed plantations.

Translocation trials to restore seed production and population viability

  • Augmentation of existing patches with additional compatible clones.
  • Creation of new populations consisting of a number of different compatible clones.

 
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