Britain’s bluebells: under threat from a foreign invader

Native bluebells (Hyacinthoides non-scripta) in Dockey Wood, Buckinghamshire

One of my favourite spring flowers is the bluebell. In UK woodlands you can find beautiful displays of common bluebell (Hyacinthoides non-scripta). The flowers can be so abundant that it can look like a blue carpet is covering the woodland floor. H. non-scripta is Britain’s only native bluebell. It is also native to Belgium, Holland, France, Portugal and Spain but is most abundant in the UK, which is estimated to have 20-50% of the world’s population (1). Unfortunately H. non-scripta now faces threats from introduced and commercially cultivated varieties of bluebells.

 H. non-scripta is closely related to another bluebell species called Hyacinthoides hispanica, native to Spain, Portugal and North Africa, and the two species can hybridise and produce fertile offspring usually referred to as H.×massartiana (see pictures below). H. hispanica was first introduced into UK gardens in the 17^th century and was found in the wild by the early 20^th century, with the hybrid first spoyyed in 1963 (2). Most of so-called Spanish bluebells found in UK gardens are actually cultivated forms of the hybrid H.×massartiana (3). It is these robust and highly fertile cultivated plants that pose the biggest threat to the British H. non-scripta.

The sweet-scented violet–blue flowers of H. non-scripta flowers (left) hang from one side of the stem. The pollen is creamy-white in colour. H. hispanica (right) has paler flowers that hang down all round the stem. Hybrid (H. x massartiana) forms have intermediate characteristics. Images by Michael Maggs (left) and Peter Mansfeld (right) distributed under a CC BY-SA 3.0 licence.

A study of bluebells in South-Central Scotland found that 10% of the native H.non-scripta bluebells were in mixed groups with non-native forms (the hybrid and H. hispanica) (1). The study also found that 40% of H. non-scripta were within 1 km of non-native bluebells, suggesting that large proportions of H. non-scripta are at risk of hybridising with non-native bluebells. The worry is that by hybridisng with non-native bluebells the distrinctive traits of the British bluebell could be lost. You could argue that because H. non-scripta and H. hispanica can produce fertile hybrids that this would have happened anyway. Maybe this is true but it certainly wouldn’t have happened as quickly if H. hispanica and the hybrid H.×massartiana had not been introduced into the UK. The activities of insect pollinators and natural seed dispersal would see a more gradual shift starting in areas in Western Europe where H. non-scripta and H. hispanica are both found. Also, we mustn’t forget that the English Channel is a rather large obstacle to pollen transfer and seed dispersal…

So what can we do to help native bluebells?

• Avoid planting non-native bluebells in areas close to native populations.
• If you would like to plant native bluebells make sure you buy them from a licenced supplier (H. non-scripta is protected under the Wildlife and Countryside Act 1981 so it is an offence to dig up and sell wild plants but there have been cases of wild populations being stripped by collectors). Sometimes hybrid bluebells are sold labelled as native bluebells so if in doubt check the colour of the pollen. If the pollen is creamy-white then it is native H. non-scripta. If it is any other colour such as pale green or blue it is non-native (5).
• If you have bluebells growing in your garden or in your local area take part in the Natural History Museum bluebell survey http://www.nhm.ac.uk/nature-online/british-natural-history/survey-bluebells/index.html
•  Support the maintenance coppice cycles in woodlands. Coppicing is a traditional form of woodland management where trees are cut down to the base and the shoots are allowed to regrow for a number of years before cutting again. Coppicing is beneficial to a number of wildflowers including bluebells because it increases the amount of light reaching the woodland floor. Today coppicing is often managed by charities with volunteers.

Hopefully scenes like the one in Dockey Wood will be around for many years to come!

References:

(1)Kohn et al. (2009) Are native bluebells (Hyacinthoides non-scripta) at risk from alien congenerics? Evidence from distributions and co-occurrence in Scotland. Biological Conservation. http://www.sciencedirect.com/science/article/pii/S0006320708003686

(2) http://www.brc.ac.uk/gbnn_admin/index.php?q=node/145

(3) Rix (2004) Hyacinthoides non-scripta. Curtis’s Botanical Magazinehttp://onlinelibrary.wiley.com/doi/10.1111/j.1467-8748.2004.00406.x/pdf

(4)NHM: Identify your bluebells. http://www.nhm.ac.uk/nature-online/british-natural-history/survey-bluebells/bluebell-identification/index.html