autumn colouring and street lighting.

[Diane]

This year my liquidamber tree in the front garden has failed to colour up - it's usually a wonderful sight with leaves of deep gold and red. This year the leaves have just managed a sickly yellow. The only thing that has changed is that the council replaced the old street lights with the new bright white lights which shine directly onto the tree. Would this have had the effect of preventing the leaves from colouring up? All the trees in the local woods and lanes have coloured up beautifully - so it seems to be just mine that has remained insipid. Any ideas would be welcome, please.

There are no other maple trees in the area (in front gardens anyway) so it's difficult to compare.

[oldherbaceous]

Dear Diane, what an interesting observation you have noticed.

Well, Liquidambers seem to always have had good colour, even in previous mild Winters, so it can't just be the cold temperatures that causes it.

So maybe light levels and the length of day light may have more of an effect.

Hopefully someone can shed more light on the matter, pun intented.

[Colin_M]

I think its correct to say that many plants are affected by day-length (as measured by the gap between sunrise & sunset). This affects both flowering in the Spring and turning & falling of leaves in the autumn.

The change in street lighting seems a very likely cause. Have you ever noticed trees that are next to or amongst street lights? Often the branches right next to the bulbs retain their leaves long after they've fallen from the the branches further away.

Round our way, the council is heading in the opposite direction: they're experimenting with turning the streetlights off during the small hours to reduce energy use, light pollution etc!

[Chantal]

Well in the real world, I work for the Institution of Lighting Professionals, so I've asked the question of our Technical Services Manager to see what he says. I'll get back to you when I have an answer.

[Chantal]

...and here's the reply

"My understanding is that the coloration in autumn has little to do with light falling directly on it but is more affected by the weather, typically rainfall at key times through the year. I could suggest that the light being close might fool the tree into thinking it's not autumn and keeping the green leaves longer, until the tree can no longer sustain them and they turn very quickly."

[Diane]

Many thanks Chantal - that is very helpful and it's the conclusion I was coming to. I'm no expert - but it seems too much of a coincidence that this is the very first time the tree has failed to colour, whilst all trees in the woods are looking fantastic - and the brighter whiter street lighting is the only new factor involved.

Much obliged.