Elms, Disease and Spalting
Elms were once a majestic and attractive tree dominating the English countryside, thanks in part to being planted extensively during the enclosure movement of the late 18th century. A mature one can reach over 35m. The dead elm we cut down was a so-called English elm (Ulmus procera or Ulmus minor var. vulgaris depending on which botanist/taxonomist you ask). The other common elm is the wych elm (Ulmus glabra). The two can be quite difficult to tell apart, even when they are alive. The wych elm has bigger leaves and seed, whereas the English elm rarely produces seed and suckers readily from the base of the trunk, which is why it tended to be planted in hedgerows. Ironically, the English elm is almost certainly not an English native. Genetic studies show English elms are genetically identical clones of a single tree and very similar genetically to elms found in Spain and Italy. They are associated particularly with Romanised areas of the British Isles, suggesting the English elm may well have been brought to Britain by the Romans, for use in training vines. The wych elm, however, is generally accepted to be an English native.
Both elms are susceptible to Dutch elm disease. The disease was first described and isolated in the Netherlands in 1921, lending the disease its name. It reached Britain in 1927 but it was a mild strain that only killed a small proportion of trees. However, in the late 1960’s a new much more virulent strain arrived that was highly contagious and lethal to European elms. It spread rapidly, such that by the 1990’s, there were hardly any mature elm trees left anywhere in Europe. The UK alone is estimated to have lost 25m trees.
The disease in Europe is caused by two species of microfungi that are spread by two species of elm bark beetle. Once infected, the tree tries to prevent the spread of the fungus by plugging its own xylem with gum. The xylem are the vascular tissues that deliver water and nutrients to the rest of the plant. The plugs prevent the nutrients from travelling up the trunk of the tree, eventually killing it. In English elm, the roots often don’t die and suckers are thrown up. These tend to flourish for about 15 years before succumbing again.
Elm wood has a coarse texture and a stepped pattern of wood fibres that make it strong and able to resist strains and splits. It was often used for chair seats, wheel hubs and sledgehammer handles. It also is very resistant to rot when permanently wet or underground, so was popular for making coffins, bridge and harbour piers and the keels of boats. In medieval Europe, hollowed out elm trunks were used as water pipes.
When we cut the trunk of our dead elm, it revealed spalting in the wood (see left). Spalting is the colouration of wood caused by fungi, usually in dead trees. Different fungi can turn the wood different colours. White rot fungi tend to bleach the wood by consuming the lignin that pigments the wood cell wall. One of the most obvious signs of spalting shown in our picture is the black lines that look like the scratches of a quill pen. These are zone lines where two patches of different competing fungi interact and erect barriers to protect themselves and their resources from each other. It is possible to induce spalting in wood by placing it in a warm, damp environment with fungi.
Spalting is prized by wood workers and turners because of the attractive patterns and hues it makes.
Both elms are susceptible to Dutch elm disease. The disease was first described and isolated in the Netherlands in 1921, lending the disease its name. It reached Britain in 1927 but it was a mild strain that only killed a small proportion of trees. However, in the late 1960’s a new much more virulent strain arrived that was highly contagious and lethal to European elms. It spread rapidly, such that by the 1990’s, there were hardly any mature elm trees left anywhere in Europe. The UK alone is estimated to have lost 25m trees.
The disease in Europe is caused by two species of microfungi that are spread by two species of elm bark beetle. Once infected, the tree tries to prevent the spread of the fungus by plugging its own xylem with gum. The xylem are the vascular tissues that deliver water and nutrients to the rest of the plant. The plugs prevent the nutrients from travelling up the trunk of the tree, eventually killing it. In English elm, the roots often don’t die and suckers are thrown up. These tend to flourish for about 15 years before succumbing again.
Elm wood has a coarse texture and a stepped pattern of wood fibres that make it strong and able to resist strains and splits. It was often used for chair seats, wheel hubs and sledgehammer handles. It also is very resistant to rot when permanently wet or underground, so was popular for making coffins, bridge and harbour piers and the keels of boats. In medieval Europe, hollowed out elm trunks were used as water pipes.
When we cut the trunk of our dead elm, it revealed spalting in the wood (see left). Spalting is the colouration of wood caused by fungi, usually in dead trees. Different fungi can turn the wood different colours. White rot fungi tend to bleach the wood by consuming the lignin that pigments the wood cell wall. One of the most obvious signs of spalting shown in our picture is the black lines that look like the scratches of a quill pen. These are zone lines where two patches of different competing fungi interact and erect barriers to protect themselves and their resources from each other. It is possible to induce spalting in wood by placing it in a warm, damp environment with fungi.
Spalting is prized by wood workers and turners because of the attractive patterns and hues it makes.