Salting streets during big freeze could kill off thousands of trees

Tree experts have warned that council workers may have killed thousands of street trees by using salt to de-ice roads and pavements during the coldest winter for 31 years.

The council's annual tree care campaign said salt damage will have killed newly-planted roadside trees and hedges, with the toll becoming clear later this month as trees belatedly try to come into leaf.

Tree Council rural programmes director Jon Stokes said salt caused damage because trees may take up too much chlorine, preventing bud openings and causing leaf scorch, curling and death.

Sodium also blocks the uptake of manganese and potassium, which are needed to create chlorophyll and can cause a "localised drought" because the soil around the roots is so salty that the tree cannot use osmosis to get water into the roots.

Stokes added: "Salt and trees don't mix. Over the next few weeks we will notice yellowing, leaf curl and, in extreme cases, death of roadside trees. People don't necessarily connect it to winter."

He said alternatives such as potassium acetate and calcium magnesium acetate are expensive but are used more often in the USA. He recommended planting salt-tolerant trees such as Silver Birch, White Poplar, False Acacia and some oak species.

Arboricultural Advisory and Information Service director Derek Patch said: "The chemicals available are used on airfields and metal bridges but are deemed too expensive for elsewhere. Potentially this could be the worst year since 1979 for tree damage by salt because there was so much snow.

"The big problem is the application rate on pavements with a man with a shovel and barrow. It's not calibrated, then do-gooder householders join in with some more." He added that salty snow was often piled next to trees to clear paths and the London Plane was the variety most badly hit by salt.

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