Mark P. Henderson

When is green?

I wrote about the stop-start but ultimately irresistible advance of spring in my previous blog, which I embellished with a few photographs taken in various parts of the Peak District during the recent mini-heat-wave. This morning (another fine sunny day), while I was walking my neighbour’s fat dog as usual, I looked at the wood at the top of the hill and saw that almost every tree is now in full leaf. The buds on ashes and sweet chestnuts and white poplars are still only just opening, but those species always lag behind the rest. These few exceptions acknowledged, the entire canopy of the wood is now a sea of…

Green?

Broadly speaking, yes. But ‘broadly speaking’ misses all the subtle differences of hue that make the colours of spring such an annually-recurring delight to the eye. Before the chlorophylls are expressed in overwhelming quantities, as they’ll be by the end of June, the leaf colours are generated by a blend of chlorophylls and other pigments, and the balance varies with species. So at this time of year the beech leaves are lime green, the sycamores emerald, the oaks olive green, the larches viridian… Only in high summer will these subtle gradations be lost and the entire leaf canopy transformed to a more-or-less uniform ‘green’.

So when is green? July and August, mainly. Not much earlier.

One of my oldest friends has what is usually called red-green colour blindness. I once ventured to sympathise with him about what is, surely, a mild handicap. “Oh no,” he replied, “I’m not colour-blind. You are.” He went on to explain that for those of us with normal green receptors in our retinas, the perception of green excludes all the other wonderful colours of nature. How much it makes us miss, he said! As a child he could never understand why people rhapsodised about the hues of autumn because for him they were there all the time. “Grass is red,” he told me, “oak leaves are ochre, beeches are yellow…” Examination of a colour spectrum revealed that there’s only a very narrow band of wavelengths that he can’t detect. He seems to have yellow receptors in place of green receptors. So he sees such colours as grass-red, beech-leaf-yellow and traffic-light-blue.

But for me, with my “normal” vision, the arrival of the various shades of green in the leaf canopy during late April and early May is still a time of magic, even if compared to my friend’s perceptions my colour sense is muted. Fairy fire, the old country folk called it, that quiet, gradual, yet surprisingly rapid “greening” of previously bare branches and twigs. It fascinated me as a child and I haven’t outgrown the fascination; I doubt if I will now, being almost seventy years old. One day there’s no sign of life; the next, the buds are beginning to open – but you have to look closely to see them. Then, two or three days later, the tree is covered with young leaves. It’s a revolution that makes no noise, causes no injury or upset, subverts or overthrows nothing except the grip of winter, and confers real benefits on whole ecosystems.

I like to watch the order of these events. For example, there are two oak trees at the south-western corner of the aformentioned wood, the corner the fat dog and I usually approach on our walks. One always comes into leaf before the other. The difference is no more than four or five days, but it’s the same every year: tree number one comes into leaf those few days before tree number two. It’s the same with the cluster of beeches at the top of Broom Hill, a quarter of a mile away; they all come into leaf in the same order, the same sequence, year on year. No tree tries to usurp its neighbour’s right to burst into leaf first.

Why? I’m not sure. I can’t see any difference in light exposure, or any significant temperature gradient. But I suppose these individual varioations confer both advantages and disadvantages. On the one hand, the earlier you come into leaf (if you’re a tree), the more food you manufacture over the course of the summer (because you have longer to do it), so the more you can store. On the other hand, the earlier you come into leaf, the more opportunities the parasites and mini-herbivores that find you appetising will have to tuck into you.

Roundabouts and swings. Once again, μεν and δε; Nature knows how to balance an argument, even if modern politicians and journalists don’t. They could learn a lot from trees if they’d take the time to look.