View From The Shed by Volunteer Shaun - FIFTY SHADES OF LEAVES

FIFTY SHADES OF LEAVES

I like to think that I can recognise most of the birds that come to visit us at RSPB Old Moor in South Yorkshire’s beautiful Dearne Valley. I can make a decent stab at working out what species many of the dragon- and damselflies are as well. But trees? No, I’m sorry, I can’t tell the difference between a Poplar and a Larch. I can’t even tell you with any certainty if we have either or both of these species on our wetlands.

This is a big shame because some of our native trees are by far the largest living creatures on the reserve, and also some of the most impressive. They contribute massively to the look of the place and provide housing and meals for many of our smaller and more mobile animals. I should know more about them.

So I did what I always do when held back by my own ignorance; I asked a grown-up to help. In just a ten minute wander she’d pointed out Hawthorn, Ash, Blackthorn, Sycamore, Elder, Silver Birch and of course our mighty old Oak, near the wet play area. I’m sure there are more but I’d become somewhat leaf-blind by this point. But at least I was now aware that we have many different species of tree on the reserve, and each is special in its own way.

We all know that birds nest in trees but, as I mentioned in my recent ‘HOME STICKY HOME’ blog, most of them only build nests in their breeding season. The rest of the year they just find the crook of a branch or other area protected from the worst of the weather and, hopefully, predators. Birds nest in a variety of trees with Rowan, Cherry, Birch and Crab Apple being their favourites due to the ready availability of food on these trees and the foliage density meeting the particular requirements of each bird species. 

At the start of September these and all other deciduous trees are going through immense changes. The gentle movement from Summer to Autumn is their most dramatic time of the year. Aesthetically, to human eyes it’s a gradual progression from one kind of beauty to another. Not worse or better, just different. We might say “I like Summer” or “I like Autumn”, but to the trees, and the other creatures who depend on them, this seasonal shift is a matter of life and death.

As you will know by now, my grasp of the sciences isn’t the best, but I do like a good bit of research and I try my best to pass that on in a simple way that even I can understand. So here’s my stab at why trees have leaves and why they get rid of them in Autumn. May my Natural Studies O-Level teacher forgive me.

In warm weather the green leaves produce chlorophyll. This, when exposed to sunlight, produces sugars which are effectively food for the tree. You might remember a word from science lessons? ‘Photosynthesis’? That’s the name for this process. Who knew that I would finally make sense of something I was taught over forty years ago? 

The reduction of sunlight hours and dropping temperatures are nature’s triggers. These are what make birds’ thoughts turn to migration and also make a tree unthinkingly remove the green colouring from its leaves. In the colder and drier months of Winter a tree would use more energy to keep the leaves healthy than they could provide in return. Therefore it makes sense for the tree to partially shut down throughout the harsher months and sacrifice its leaves. A tree with no leaves uses much less energy and can usually survive through to the next Summer on what it has stored up from the warmer months. Instead of using the stored energy on keeping the inefficient leaves going, the tree instead concentrates on maintaining its roots. The darker months are the tree’s prime underground growth period. 

At the start of Autumn the green chlorophyll is leached from the leaves. This reveals the underlying yellow colouring produced by other chemicals. Then, as more chlorophyll and all the liquids are drained out, the leaves turn orange or red and finally a brittle brown. They are almost completely drained of sap at this time and a good thing too. Any plump, green leaves left on a deciduous tree would freeze over winter. Ruptured leaves would be disastrous for the tree, so it dispenses with them entirely, usually with the help of a good strong wind. 

I’m sure you’ve seen a tree, fully laden with healthy green leaves, swaying slightly in a summer breeze? Now imagine that same tree under attack from a terrible Autumnal gale. The wind would grab those leaves and rip branches around, endangering the structure of the entire tree. You’ll have seen it happen, perhaps even during recent storms? This is another reason why trees shed their leaves at the start of Autumn. By the time the worst of the weather hits, most of their leaves will have gone and the wind can more easily blow between the bare branches, thus reducing the risk of serious damage. It’s perfect timing. Nature does not believe in coincidences.

So those are the changes we can look forward to seeing in the coming weeks. It’s going to be interesting, dramatic and wondrous. Of course the science of leaves is much different for coniferous trees, those that have needle-shaped leaves instead of broad, flat ones and retain them throughout the year. That would be a whole different lot of research to undertake. Thank goodness that most of Old Moor’s trees are deciduous ones.

They may not be the most mobile of our residents but the Dearne Valley would look hugely different without its trees - as it once did when it was an industrial wasteland once described as “the most polluted place in Europe”. Perhaps it’s time for me to dig out my Handy Dandy I-Spy Book of Old Moor’s Old Trees?