Amazing Aspens – Muir of Dinnet NNR

Welcome to an extra- special blog dedicated to the aspen tree. Why? Well, they’re in flower this year…and that’s REALLY unusual. The last time there was a major flowering of aspen in Scotland was in 1996, that’s (quick count on fingers) 23 years ago. So, what were you doing in 1996? Personally speaking, I was midway through an extremely mediocre university career but it’s also the year of the Dunblane massacre and Dolly the sheep. And that was the last time there was a large-scale aspen flowering in Scotland.

Male aspen catkin

I must admit, I nearly didn’t spot the catkins that herald the flowering. I was walking along the path and had seen a perfectly innocent cranesbill that had, until close examination, resembled the invasive piri-piri- burr. I had just given it the evil eye and checked it wasn’t piri-piri, when I spotted what looked like a large hairy caterpillar on the path. A cautious prod (some caterpillar hairs irritate the skin) revealed it was vegetable, not animal, and that led to a look around, then up.

It’s not a hairy caterpillar after all!

Wow! The aspens are covered in catkins! Never seen that before!

Aspen tree laden with catkins

The aspens look like they leaves at first glance

Bu if you look closer, you see they are catkins

Aspen catkins

So why is this aspen flowering unusual?  Well, aspen tend to reproduce asexually – they send up shoots (called suckers) from their roots. These grow into trees in their own right, but, genetically, they’re the same as –a clone- of the parent tree. So you can look at an aspen wood and, genetically, it’s all the same tree. But that’s okay, aspen don’t mind this and will tick along quite happily doing this for years.  In fact, about 80,000 years in the case of the Pando aspen in Utah. It covers over 40 hectares and has more than 40,000 trees, but they’re all clones and are all, genetically, the same tree. So asexual reproduction works pretty well for aspen!

Aspen sucker – a clone!

Now, you might be wondering why we get so excited about aspen. Well, it’s a stunning tree in its own right, with long, straight grey trunks and, in autumn a shower of golden leaves. But it’s also quite rare…while widespread as odd trees here and there, there aren’t many aspen woods in Scotland. And where you find aspen woods, you almost always find lots of other rare things associated with them Like aspen bristle moss, thought to be extinct in the UK until the 1990’s, when it was found here and in Strathspey. Or aspen hoverfly. Or large poplar longhorn beetle. Or chocolate-tip moth (thanks to Harry Scott for pic). Or several different types of fungi – the list goes on and on.

Aspen woods

Aspen woods in spring

Aspens go the most vivid golden colour in autumn

Aspens in winter

Holes made by large Poplar Longhorn Beetles in aspen

Chocolate tip moth

Aspen trees can be male or female but you can’t tell which until they produce catkins. These are the male catkins. They are larger and dangle more (large, hairy, dangly = male, if it helps you remember) than the female ones, which tend to protrude rather than dangle. There is a good online guide to sexing aspen here http://www.highlandbiodiversity.com/userfiles/file/newsletters/SEXING-ASPEN-Trees.pdf?fbclid=IwAR3Ma4sBVxMArIY7cHJrXX9-71NkwsTkE6uXk44hwpQ5YOVfEe2tN1iRTbs  and we and other folk will be heading out to sex our aspen trees. If we can find female trees, we can maybe gather seed to help plant, spread and preserve aspen in Scotland. If you want to find out more, or report any sightings of aspens with catkins, the Scottish Aspen website is http://www.scottishaspen.org.uk/ .

You can see the size of them alongside my hand.

Aspen catkins can easily be 6-7 cm long

Red anthers

Aspen catkins

It’s hard to tell why the aspen has chosen this year to flower but it may well have been triggered by the long, hot, exceptionally dry summer we had in 2018. 1995 had a very hot, dry summer too, and the fact that aspens have flowered the in the year after these extreme summers suggests there may be some sort of link. Maybe the dry weather drought-stresses the trees, so they hurry to reproduce in case they die. Or maybe not – maybe aspen just like the heat. While we can’t be sure what has caused the flowering this year, it has given us a rare opportunity to see it. Get out soon (within the next fortnight) if you want to see it – it could be another 23 years until your next chance!

Aspen catkins – male

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