Road salt injury
Damage, symptoms and biology
In northern countries, the use of abrasives and de-icing salt is necessary for ensuring road safety in wintertime. The main de-icing chemicals used are NaCl (table salt) and CaCl (calcium chloride). Build-up of salt, abrasives and mechanical shock are the main causes of mortality in trees growing near major arteries. The symptoms of salt exposure resemble those of summer drought. There is a decline in leaf surface area, yellowing and then browning of foliage, followed by premature leaf shedding. Another frequent symptom is bud destruction or abortion. A reduction occurs in the tree's overall vigour and its growth. The presence of salt reduces the availability of water and minerals because absorption becomes blocked owing to destruction of the root system by corrosion. When the de-icing chemicals enter the tree, they have a toxic effect on the cells and impede some crucial enzymatic reactions. The tree ends up dying of exhaustion and generalized intoxication that prevents it from carrying on the activities necessary for its maintenance.
The most effective de-icing mixtures contain proportionally more CaCl than NaCl. NaCl has the most damaging effect on trees. Unfortunately, CaCl is more costly to use.
Canadian Forest Service Publications
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