Stress likely cause of trees losing leaves

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A dry and hot summer has caused some poplar trees in the Teviot Valley to turn yellow and shed their leaves early.

The phenomenon has prompted comment on social media.

Stephanie Sommers, of Roxburgh, posted photos on Facebook with the comment: “It’s only January 20 – what is this all about?”

On the way to Dunedin, Mrs Sommers noticed the trees and stopped to take some photos.

“It was a very surreal experience watching all the leaves falling to the ground as I photographed these trees,” she said.

“It is strange that a scene normally associated with great beauty could be in truth more foreboding, in that the early changing colour of the leaves could actually mean these trees were dying.”

Is it autumn? . . . Stephanie Sommers,of Roxburgh, is surprised to see these poplars near Ettrick shedding leaves. PHOTO: STEPHANIE SOMMERS

Central Otago District Council parks team leader Ian Mann said he was not a qualified arborist but that it looked like “early senescence”.

“This is the process when trees shut down for the winter and stop producing chlorophyll which is the ‘green’ chemical that all plant life use for photosynthesis.

“Deciduous trees actually start this process quite early ahead of autumn; it is a slow process that results in the autumn colours appearing at this time.

“Trees will shut down earlier if they are under stress, as a defence mechanism to external influences like drought,” Mr Mann said.

The extended dry and hot spell since spring meant trees were under stress as they had not received adequate water for their processes, he said.

“Rather than ‘risk’ disease or death, they shut down, cease photosynthesis and shed their leaves, as a survival mechanism.”

Mature trees could consume up to 57 litres of water per hour on a hot day, Mr Mann said.

“If this supply is not there, the trees will start to die back due to drought. To avoid this they shut down.”