Saving a Rare Species – The Plight of the Elm

East Dartmoor Woods and Heaths National Nature Reserve is just one of over 200 NNRs across England, and Natural England designate these areas to “protect some of our most important habitats”. These conservation areas are widely varied but, here in the woods of East Dartmoor, a team of volunteers is helping to conserve a tree that, over recent decades has become scarce and, while being worthy of protection itself, it also holds the key to the survival of a rare butterfly.

trendlebere landscape
East Dartmoor Woods and Heaths – view of Hisley Woods from Trendlebere Down

The wych elm is one of the species that is at risk from Dutch elm disease, a fungal pathogen spread by elm bark beetles. The disease was researched by Dutch scientists who discovered how the beetles, feeding under the bark of the elm, would introduce the fungus which interferes with the water conducting systems in the tree. Visible signs of the disease are the yellowing of leaves which then turn black and drop from the tree, then whole branches will die back before the crown is affected and the tree can die.

During the 1970s and 1980s elm trees across the country were dying and being felled in an attempt to limit the spread of the disease. The majority of the larger specimens were lost. Today the general opinion is that wych elm is less favoured by the elm beetle and therefore is, in some respect, more resistant than the English elm. Wych elm favours sites with high humidity and at Rudge Wood and the Woodland Trust’s Hisley Wood in the River Bovey valley, the conditions are good. A number of elms still stand in these woods and, though Dutch elm disease is present, they are surviving. This may be good news for the declining population of white letter hairstreak butterflies that feed almost exclusively on elms.

The plight of these elms and the associated moths and butterflies has inspired a group of Nature Reserve volunteers to help and, last autumn, they started to search the woods to find and record all the wych elm trees in the valley. The trees were found all through the broad leaf woods, often in clusters and at varying stages of maturity. The volunteers found them easier to see in the autumn as the foliage turns to bright yellow and again in the spring when the pale green clusters of winged seeds form before most of the leaf canopy appears, giving away their location.

elm seeds Apr 17
Elm seeds are visible in clusters before the leaves have developed.

The volunteers have put in a lot of time and energy to this project, spending many days climbing through the wooded hillsides to locate, record and plot each elm tree. They have been looking at the overall health of each tree, measuring its girth and making recommendations on how their habitat can be improved. When out surveying trees in Rudge Wood, Nikki, the lead volunteer made some observations. “This one is in the sun but it’s partially shaded by the big oak. It’s a good tree – it’s healthy”. She spotted some new shoots, growing on the sunny side of the tree. They were growing fast but could be out competed by an adjacent sycamore. “We may need to do some management by cutting back the sycamore to give the elms some space”, she explained.

The conservation plan is also being extended to propagate some of the elms. During the spring, a batch of seeds have been collected and are being grown into saplings, ready for planting in strategic positions around the woods. Albert Knott of Natural England described how “we need to maintain the connections between the clusters of elms so, if we can plant elms we can support the white letter hairstreak”. Some elm cuttings have also been taken which will be grown on and planted in the woods. Later in the summer a white letter hairstreak training course will inform the volunteers and workers who, in the future, will be able to monitor the numbers of rare butterflies feeding around the elm trees.

To be continued ….

Information on elm trees and Dutch elm disease

White letter hairstreak information

by Matt Parkins

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