Twinflower in the UK

Twinflower in the UK

Laurie Wildwood

Wednesday 18th January 2023

Laurie completed a thesis on Twinflower (Linnaea borealis) for Trees for Life in 2010 as part of a masters degree. His aim was to investigate the environmental conditions in which Twinflower grows best so that the information could be used by land managers, for example, in reintroduction projects. If you see abundant flowers of this pretty plant in a Caledonian Pine Forest, it may make you think the plant is doing well, however, abundant flowers doesn’t necessarily mean that the conditions are right to enable the plants to set seed.

Twinflower is a member of the Honeysuckle family (thanks Mavis for confirming this at the talk!). It has pendant pale pink flowers in pairs on flower stems up to 8cm tall and the small, oval-rounded leaves grow in opposite pairs, on stems that trail along the ground. In the UK, it is mainly found in pine forests in Scotland, particularly near the Cairngorms. Globally, it has a circumpolar distribution, mainly in forests in the Northern Hemisphere where it is fairly widespread. Twinflower is nationally scarce in the UK and it is thought it used to be more widespread across Scotland and northern England. Habitat loss and fragmentation of populations are thought to be the main reasons for the decline in UK distribution.

Twinflower requires cross-pollination to produce viable seed, however it is able to spread vegetatively by stolons (overground runners) to produce clonal patches, enabling it to hang on in sub-optimal growing conditions. Habitat loss has meant that clonal colonies have become isolated from each other, making the plants much more susceptible to stress and disease and without viable seed, they are unable to colonise new sites. Sometimes new populations are stumbled upon but often these are due to forestry machinery spreading the plants vegetatively. Conservation efforts are taking place in Scotland both to reintroduce the plant to new sites and to undertake translocation work at existing sites to bring together plants of different genotypes so that they are close enough for pollinators to travel between them. The long-term aim is that the plant will become self sustaining in Scotland. Ideally, we need more connectivity between habitats to enable Twinflower to spread via seed on its own.

Laurie mentioned Dr Frans Vera, a Dutch biologist and conservationist who hypothesised that European primeval forests were not a closed-canopy but were a cyclical mosaic of habitats and the semi-open landscape was maintained by the presence of large herbivores. Laurie found that Twinflower seemed to grow best under a dappled, light tree canopy, a habitat that may have been more abundant in the past. The ability to grow vegetatively may have helped the plant survive under a denser canopy until more optimal conditions returned.

Laurie visited various known populations of Twinflower in Scotland and recorded data such as aspect, altitude, shrub height and amount of shade from the tree canopy. Laurie showed photographs of other wildlife he saw whilst surveying for Twinflower, such as crested tit, pine martin, mountain sorrel and one-flowered wintergreen. Laurie analysed the results and found that Twinflower was most abundant on south or west facing sites with a low shrub height under a tree canopy of moderate dappled shade. This may indicate it is a coloniser of disturbed sites. Laurie also looked at the plant communities associated with good and poor sites, which may be of use when looking for new re-introduction sites. For example, Wavy Hair Grass (Avenella flexuosa) and the moss Hylocomiadelphus triquetrus (formally known as Rhytidiadelphus triquetrus) were often associated with healthy-looking patches of Twinflower.

Andy Scobie, who works for NatureScot, has been heavily involved with the conservation of Twinflower in Scotland. Laurie recently contacted Andy and asked for an update on recent conservation efforts. Andy said that some translocation work has been done and some smaller-scale landowners are managing sites for Twinflower, however, in general, management to control deer numbers is not taking place at a larger scale due to conflicts with the needs of other species such as capercaillie, which has different habitat requirements to Twinflower. Guidelines for the conservation of Twinflower have been produced: The Twinflower Restoration Handbook. Laurie concluded that the future for Twinflower in the UK may not be bright but it is certainly less bleak than it was.

Laurie recommended a beginners book to bryophyte identification by Dominic Price and Clive Bealey called A Field Guide to Bryophytes which has recently been published. I did a quick online search and found the following websites giving further information about Twinflower conservation in the UK:

https://www.plantlife.org.uk/scotland/blog/taking-action-for-twinflower

https://community.rspb.org.uk/ourwork/b/science/posts/planting-a-new-bridge-for-twinflower-in-the-cairngorms

https://bsbi.org/wp-content/uploads/dlm_uploads/Twinflower-Research-conservation.pdf

Text and photograph by Susan