Added on 29/12/2011Article

The Decline of the Elm.


The Elm was a common sight within the English countryside, but with the spread of Dutch Elm Disease, almost 50% (12.5 million trees) of the mature Elm stock had been wiped out by 1977.

History


The three dominant Elm species within the U.K were the Wych Elm (Ulmus glabra), the English Elm (Ulmus procera) and the Smooth Leaved Elm (Ulmus carpinifolia) with the Wych Elm being generally accepted as our native Elm. It is thought that the Smooth Leaved and English Elms were introduced from Europe probably by the Romans. Pollen records show that the Wych Elm existed after the last Ice age and along with the Oak dominated the forests. With the advent of forest clearance and the agricultural needs of man, the Elm declined and became, in the south, a field and hedgerow tree; the harsher farming conditions in the north allowed the forests of Wych Elm to survive.

During the 16th to 18th centuries the Elm decline slowed as the enclosure Acts forced land owners to create and maintain boundaries. Hawthorn and Elm were included as the planting species with many Elm suckers growing on into mature trees. During the 18th and 19th Centuries Elms were also planted in parklands and as avenues for stately homes. Windsor park once contained a 2 mile long avenue of Wych Elm running from the Castle to a hill top statue. So abundant was the Elm that in 1838 it was referred to as the second most common tree in parks after the Oak.

Elm was used throughout history as a source of fodder, fuel and as timber. Its leaves and shoots could be regularly cut from suckers and fed to livestock. Its wood was tough and difficult to work but still found uses in wheelwrighting, ship building, furniture making and for use under water as lock sills, pilings and pipes. With the River Thames polluted, much of old London received fresh water through Elm pipes. London's old Waterloo Bridge rested on Elm piles and when this was removed in 1936, large quantities of sound timber were extracted, having laid there for 125 years.

The Disease


The Disease known as Dutch Elm Disease was discovered in 1918 in France and was later identified in Holland, which is how it obtained its name. It quickly spread into England and had, by 1930 wiped out 20% of the Elm tree stock, the outbreak peaked in 1936. A new, more severe, outbreak occurred in the late 1960's with the source of infection traced back to the sea ports of Southampton, London and Avonmouth. The disease was being carried in Elm logs which were being imported from North America. By 1977 almost 50% of the mature Elm stock had been wiped out (some 12.5 million trees lost).

The actual disease is a fungus (Ophiostoma ulmi) which invades the Xylem vessels of the current growth ring and quickly girdles and kills the stem. The latest outbreak which started during the 1960's features a more aggressive strain of the fungus (Ophiostoma novo-ulmi) and like the original strain, only attacks Ulmi and Zelkova species.

The disease spreads from tree to tree by way of Elm bark beetles (the Scolytus species). The beetles feed on the young, sappy bark found within twig crotches; here the fungal spores carried on the beetles enter the trees transpiration system. The fungus spreads and produces toxins which affect the trees health. Meanwhile, the female beetle burrows into the Elm bark and lays her eggs along a straight tunnel. Once the larvae hatch they each head off at right angles from the central gallery eating and forming their own individual tunnels. The larvae then pupate and emerge from the ends of their feeding tunnel by burrowing back through the bark. As they emerge to fly to new trees, they inadvertently complete the cycle by picking up fresh fungal spores.

The following photograph shows a section under the bark where the gallery produced by bark beetles can be clearly seen.