Saturday, 7 January 2012

Trees and Winter Gales

I suppose that if you live around Chorlton Green, or have visited it in the last couple of days, you will have noticed that one of the Lime trees that grow around the edge of the Green has been blown over.

I think that this happened either late on the night of Wednesday 4th January
or early the next morning.

This tree grew at the north-west corner of the Green and I suspect that that night’s gales were channelled and amplified as they blew down Albemarle Road - making a tree on that particular corner very vulnerable.
In spite of this loss we have escaped very lightly compared to the Royal Botanic Garden in Edinburgh (where the recent gales have been much stronger than those that we have experienced in South Manchester). A report (see ref. below) on the damage to the gardens states that:
“... it will take much longer to replace more than 40 trees blown over in the storms. They include some specimens which were hundreds of years old, and others which were important in the history of the collection.”
The report continues:
“Dr Edwards (a spokesman for the Gardens) [showed the reporter] a huge native oak which had stood more than 15m (45ft) tall, but had been felled by the winds.
"It's a lovely big specimen tree. Or it was. It's now lying sadly on its side," he said.
"But even though this is a big tree the roots don't go down very deep. They actually only go down about two metres (6ft) into the ground. That's often surprising for people."
But the collapse of the tree has allowed experts to see, for the first time ever, what has been going on in the very uppermost branches of these trees.
"This is very exciting for me", Dr Edwards explained.

"These branches are absolutely covered in lichen. And it's not just one species of lichen. There's a whole variety - some of them growing quite luxuriantly."

That matters because lichens are highly sensitive to environmental pollution.

"The fact that there are so many lichens growing here, and they're looking so healthy, is evidence that Edinburgh has got cleaner over the past few decades."

Dr Edwards said the loss of such a tree was "a tragedy" for RBGE.

But, he added: "In some of the more natural woodland areas, this could be seen as nature's way of pruning out diseased and damaged branches and trees.” ”

With this report in mind I went to have a look at the fallen tree on the Green. Sure enough the roots were surprisingly shallow and the upper branches were adorned with lichens (and mosses and, what I assume, is some sort algae). I suspect that the lichen flora on our felled Lime is not as diverse as that on the Edinburgh Oak – but I don’t know enough about lichens to be sure.
Perhaps the saddest thing about this particular loss is that the tree’s twigs bore abundant buds – just waiting to burst forth in the coming spring; this, of course, will never happen now.
During previous winter gales we have lost several trees on Chorlton Ees. The trees there are particularly prone to wind blow after prolonged rains - which soften the ground. I don’t suppose that I need to remind anyone that we’ve had lots and lots of rain recently and the ground is
very soft indeed.
After I’d examined and photographed the fallen tree on the Green, I walked over to the Ees to inspect any damage there. To my great surprise I couldn’t find a single fallen tree (apart, that is, from those blown over in previous years). It could be that the winds were not as strong this winter as they have been in previous years; but another possibility occurred to me:
The trees on Chorlton Ees were planted around 40 years ago. They were planted too close together, have rarely been thinned and, as a result, have tended to grow tall and spindly. In addition, because they are planted trees they have, almost by definition, weakened roots (digging up a tree and re-planting it tends to damage its roots). When these trees reached an optimum
height they became vulnerable to wind blow. But successive winter gales, over the last few years, have now winnowed out the weakest and most vulnerable trees.

From now on fewer will blow down and those that remain may even have stronger
roots (I suspect that the bending and flexing that goes on during gales may
strengthen the roots in such a way that they are more able to withstand the
prevailing winds). I should stress that this is just a hypothesis and don’t be
surprised if we lose more trees if we get more gales this winter or in
subsequent years.
In a spindly plantation, such as that on Chorlton Ees, the loss of
a few trees to gales is no big deal and tends to add to the biodiversity of the
site by letting in more light. In addition, as the fallen trunks rot they form
a habitat for various invertebrates, fungi, mosses and ferns.
Dave Bishop, January, 2012
Reference: 'Worst ever' storm damage at Edinburgh botanic
garden By Huw Williams
BBC Scotland reporter,
BBC News, Edinburgh, Fife & East
Scotland, 05.01.2012 (

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