Survey Tips - how to find elm

Andrew Middleton and Liz Goodyear have been looking for Purple Emperor for several years, and this work has focused their attention on assessing aboreal habitats and their associated species. They have found that many of the techniques that are so useful in surveying for Purple Emperor can also be used to find White-letter Hairstreak, and these tips reflect that experience........

Link sections on this page . . .

	Survey tips and recording notes index page

For more information on Elm and elm identification visit the London Natural History Museum website

HOW TO FIND ELM

Identifying Elm
It is important to know what an elm looks like!  Most people will say there is no elm in their area or that it is all dead.  The elm people see is dead because it stands out in the landscape.  However, there is often healthy elm nearby which no one notices.  When we started looking for Purple Emperor, the first thing we would do when surveying a new area out of season was to search for sallows, the larval food plant of the caterpillar.  Once we had established if sallow was present we would then grade it on quality and quantity.  The difference with elm and sallow is that whereas for Purple Emperor we would reckon on at least 300 sallows needed to be present, we have found that White-letter will survive on what appears to be only a handful of elms.

To find sallow we would, in the early days of our work, go out in the spring when the catkins were in flower, and look across to a wood and just see where the sallows were by looking for the 'yellow blobs' of trees in a woodland canopy or along hedge lines, often through binoculars. You didn't need to be that close. The same can be done for elm in spring when they are covered in thousands of pale green seed discs, which turn to yellow then brown. Even small trees often seem to be covered - this can help in finding healthy elm, as well as the more obvious dying trees, as one travels around in spring. You then notice all the elm you never knew existed! However - elm not seeding does exist.

This view of elm in TL4210 was seen from the far side of the field in July 2006 and was the last 2km square to be found in TL41. It was necessary to walk to them from the adjacent 2km square but I could see from some distance I was walking towards elm! (Photo taken in the autumn but the distinctive habit shape is still visible)

As we have become more experienced we can now quite easily identify a sallow tree even in winter by simply looking at its shape and habit, and its trunk, and double checking by looking at the leaf litter on the ground beneath the tree. We are also beginning to be able to do this with elm. However, the experienced egg hunter will have no difficulty in spotting an elm in winter!

Two rows of roadside elm near Ware photographed at the beginning of February - buds are already visible. Both sites had White-letter records in July 2006 and some die back can be seen. More winter habitat photos are shown on the photos page....

Once summer comes, elm tends to lose this strong visual identity and just becomes another tree. However, once again it doesn't take long before you see the shape of hedge-row or field edge elm in the landscape from some distance.

However, its also possible to miss quite large elms, many of which are still in the landscape as we often found out in the autumn.

A row of mature elm trees found along an old track (Cox Lane) near Much Hadham whilst surveying in the autumn

This cluster of mixed elm trees (viewed from 3 directions) was found close to the River Stort near Sawbridgeworth. All the leaves were different and we actually walked under the large tree without noticing it!

Thoughout the year, Andrew has collected a variety of elm leaves, looked at them under the microscope, done some reading around, and now realises that he has no reason to be sure of his elm identification. Even the experts disagree on how many species there are and when John G Dony wrote the Flora of Hertfordshire in 1967 he said "The Hertfordshire elms have caused botanists much trouble." He also felt unable to create any distribution maps! Oliver Rackham writes in The History of the Countryside - "They are the most complex and difficult trees in western Europe....." We don't look for specific elm species, just because the books say they will be found on one and not the other - WE LOOK AT ANY ELM!

Three different elm leaves seen through a microscope, showing how under close inspection they are so different Upper row - upperside Lower row ~ underside Left ~ smooth above with some red glands, soft hairs below esp. axils ~ possibly smooth-leaved type U.minor Middle ~ some brittle hairs and some red glands above, numerous red glands & hairs below ~ English elm U.procera type Right ~ many coarse hairs above, no red glands ~ possibly Wych elm U.glabra type 'Red glands and spiny hairs on English/Atinian Elm and the documented history of the tree', Ken Adams, Essex Field Club newsletter No 46 January 2005 p.14

Over the year, we have found that a lot of people don't recognise sallow, and we just remind them that they are the trees with pussy willow catkins on them in the spring. With elm it's much harder to explain, but for someone new to elm, the easiest way to confirm it's an elm leaf is to rub it and if the leaf feels rough then its almost certainly an elm leaf. However, just to confuse matters there is Smooth-leaved elm u. minor, which has smooth leaves. Another way to identify an elm leaf is the uneven leaf bases (as long as you examine a sample of leaves).

A selection of elm leaves collected by Andrew Middleton, which shows the variety of shapes and sizes that can be found but the uneven base shows in most of the leaves!

Liz Goodyear and Andrew Middleton
January 2007