TDA 135 Poisoned in Ignorance
Tree Damage Alert No 135
15th Jan 2010
Poisoned in Ignorance
Reports of Councils running low on stocks of grit and salt have implications for the continued smooth running of traffic. That is the first thought, but what is the possible longer term outcome of this winter’s snowfalls?
Does the lack of salt and grit indicate a lack of stockpiling due to a false sense of security perhaps as a result of winters of late tending to be grey and wet rather than white and Christmas cardy? Or should we have genuine concern about the amount of salt and grit that has been thrown around during this winter?
In recent years roads have been treated because of a risk of ice forming. Such salt applications melt any ice and are then washed away by the water. Furthermore, the typically British winter rainfalls dilute the saline solutions running off roads which limits the risk of environmental damage. When snow falls and is treated with salt and grit a very different scenario develops.
Snow may fall on salted road surfaces and initially it may melt. However, as snow continues to fall, the salt becomes less effective. The grit element of the treatment may have a prime role in maintaining traction. If the snow continues to fall further applications of salt and grit persist in the snow on the ground where it remains environmentally benign until a thaw.
Unfortunately, in towns snow is moved by snowploughs, scrapers and even brush and shovel to form piles awaiting the thaw. Where are these piles located? Usually in positions that are least used by the public and vehicles – that is often around trees. Salt laden snow them thaws and the toxic salt is released directly into the ground around trees.
The snow, once it has melted, will be largely forgotten, but the impact of the salt will only become obvious during the spring when roadside and street trees flush weakly or fail to flush (Dobson 1991a). But it is too late then to contemplate remedial/preventative action because the damage has been caused. It is important that arboriculturists act now before the snow melts. Advise colleagues in Highways and Environmental Health Departments of the environmental impact salt can have on trees and the environment more widely. Remember their actions are in response to a threat to public safety and the working of society – it is not wilful, but a lack of knowledge. It is up to us to educate colleagues about the needs of tree roots and the damage that can be so easily and unwittingly done to them. Encourage the application of salt, whether to roads or paths, through calibrated equipment (Dobson 1991b).
Snow will persist longest where it has been piled and compacted, that is often around the bases of trees. Encourage removal of those piles of ‘discarded’ snow to less environmentally threatening positions.
Rationing salt and the Government’s direction to reduce its usage by 25% will not reduce the threat of damage to trees and vegetation. The clock is already ticking.
Derek Patch and Brian Greig, AAIS, Farnham.
AAIS l Alice Holt Lodge l Wrecclesham l Farnham l Surrey l GU10 4LH
Call the Tree Helpline on: 09065 161147
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References
Dobson, M.C. (1991a) Diagnosis of de-icing salt damage to trees. ARN 96/91/PATH
Dobson, M.C. (1991b) Prevention and amelioration of de-icing salt damage to trees. ARN100/91/PATH