16th November 2021
Autumn has arrived.
Someone asked me about autumn colours the other week (27th October to be exact), and if I could describe them. I had a good look around (just to check) and had to say there weren’t any really, it was too early. In the days before All Hallows’ Eve and Guy Fawkes Night that seemed odd, but true.
Admittedly the birch and beech trees weren’t quite as green as they had been, but there just wasn’t the kaleidoscope of reds, oranges and yellows that was expected.
Now, a couple of frosts and 2 weeks later even those yellow leaves have all but disappeared, the drop in temperature after a long dry spell and some storms having turned the season very quickly.
So what happens? What is going on with this radical change – and I’m not talking about the climate crisis here – but the biological processes that are happening within those most magical and stately beings: trees.
Like all (green) plants trees photosynthesise, that is, they have the ability to turn sunshine, carbon dioxide and water into energy (sugars) and oxygen. They have structures called chloroplasts, containing chlorophyll, within the leaf cells where the conversion (magic) takes place. Generally, chlorophyll is green (but there can be red, brown and blue pigments) hence the colour of leaves in the sunnier, summer months.
The process of photosynthesis carries on until the amount of (day)light and temperatures begin to drop. Shorter days mean less sugar is produced and this triggers hormones to be released which ‘seal’ up the leaf, stop the energy producing processes within and reclaim any useful chemicals for next year.
The green chlorophyll is the first to go revealing other colours ‘beneath’:
“These include yellow flavonols, orange carotenoids and red to purple anthocyanins. The exact mixture of these compounds varies between species, and hence the degree of yellow or red colour in the leaves.” – Royal Botanic Gardens Kew
No leaves, no energy. No energy, no growth. (Deciduous) trees enter a dormant phase during the winter, a bit like hibernation, which is why this is the best time to plant them (this year’s National Tree Week begins on the 27th November) and help nature’s magic life-giving, oxygen-producing gentle giants help us.
Something else that’s pretty magical is mushrooms – or technically fungi. (As is the language used to describe them!)
Popping up all over, amazing colours and shapes, then having done their bit, which is to reproduce, get all mushy and disappear again.
What we see is the proverbial ‘tip of the iceberg’ – the mushrooms are the ‘fruiting body’ produced to spread spores and therefore the species. Underground (or under bark) there is a huge network of hyphae, or collectively a mycelium – root-like fibres which push outwards and onwards breaking down organic material (such as dead leaves), making the raw materials available again for use throughout the system. Top candidates for ‘Heroes of the Earth’ mycelia are of vital importance to the soil, 92% of plant families interact with fungi, including trees. This kind of ‘symbiosis’ is called a mycorrhizal relationship and you can buy solutions to use as root dips when you are tree planting to kick start this.
Mycelia (the individual hyphae) are also an important food source themselves for insects and other invertebrates.
The world’s largest organism is a fungus. Its mycelium can allow a fungus to occupy an enormously large area.
A fungus, Armillaria Ostoyae – a type of honey fungus, that lives in the Blue Mountains in Oregon (USA) occupies ten square kilometres and is believed to be at least 2400 years old.