Elm trees and butterflies

Posted: Friday 9 May 2014
by Kate Bradbury

I spent the Bank Holiday weekend in Brighton, and ran around Preston Park admiring its lovely elm trees.

I spent the Bank Holiday weekend in Brighton, and ran around Preston Park admiring its lovely elm trees. Most had just come into leaf and their tiny, papery fruits – known as samaras – were scattered on the pavements below.

According to the Brighton & Hove City Council website Brighton has always had a large population of elms, which were mostly planted by the Victorians and Edwardians. Elms are well suited to Brighton, owing to their high tolerance to thin chalk soil and salty sea winds.

The city is currently home to around 17,000 elm trees, which is quite something for a species ravaged by Dutch Elm Disease. Indeed, the successful control of the fungal disease – the spread of which is exacerbated by elm bark beetles – earned Brighton and Hove the title of the National Collection Holder of Elms. I wasn’t just running around the local park admiring a few (now) rare trees, I was running among the National Collection, which includes English (Ulmus minor var. vulgaris), Jersey (Ulmus minor subsp. sarniensis) and Cornish (Ulmus minor subsp. angustifolia) elms, as well as two very old specimens known as the ‘Preston Twins’.

One of the many lovely things about elm trees is how easy they are to identify (at least to genus level). The ribbed leaves have a characteristic asymmetrical base and taper to a sudden point at the top. The circular green samaras are wonderful, too, each one fading to brown and revealing a single reddish seed at its centre. But my very favourite thing about elm trees is the butterfly which depends on them – the white letter hairstreak, Satyrium w-album. Named after the series of white lines on the underside of the hindwings which appear to form the letter ‘W’, this species suffered massive declines in the 1960s, 1970s and 1980s, as Dutch Elm Disease killed some 250,000,000 trees. An elusive butterfly, it flits among the tree tops, but it does so in Brighton’s busy Preston Park and The Level, as well as other surprisingly urban spaces. I’ve never seen one, but I intend to now.

Currently the white letter hairstreak only feeds on the flowers of wych elm, small-leaved elm and English elm, but in the last few years a new hybrid has been used in municipal street plantings in Brighton and Hove. Ulmus ‘Lobel’ has parentage of wych elm, Himalayan elm and Dutch elm, and shows good resistance to Dutch Elm Disease. Wouldn’t it be wonderful if the white letter hairstreak adapted to breed on this disease-resistant hybrid, offering a ray of hope to both the butterfly and the elm?

Many thanks to Martin Warren / Butterfly Conservation for kind permission to use the lovely image of the white letter hairstreak butterfly.

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oldchippy 09/05/2014 at 14:34

Nonsuch park jointly managed by Epsom & Ewell And Sutton councils has quite a population of Elm growing from suckers also on the road side there are some more looking good,I hope every year they will come back so far so good.