It’s the beginning of winter: a time to look at trees’ anatomy; to coppice and fell; to plant seedlings before the hard frosts come, and also to admire. But for me this national tree week started with a revelation. I have been pruning an old, outgrown hawthorn hedge and weaving the cut branches between the stems to keep deer out of a new plantation that they have been munching on. I have no idea how I got to the age of fifty-three without ever having been jabbed by one of their barbs, but it must be so. I would have remembered. Two small pricks swelled up on the back of my hand and within hours I felt like I must have punched someone – my knuckles were stiff and sore, swollen red. Two days later my hand was back to normal; but it happened again, and this time I went online to see what the world had to say. The answer was a string of posts from people experiencing the same thing; and then the answer, from a plant biologist who says that hawthorn concentrates bacterial pathogens in its thorns to deter herbivores. Which just goes to show that however much you think you know about trees, you learn something new every day.

Today’s encounter with trees was very different. There was an overnight frost; by ten this morning the skies had drawn back to leave a day of startling clarity and crisp, clean light in which landscape features were chiselled sharp against the sky. I have been conducting an archaeological survey, with colleagues, at a place called Heavenfield in Northumbria, right on Hadrian’s Wall, where Prince Oswald famously camped the night before recovering his kingdom in battle in the year AD635 (For that story you must read The King in the North). We are running a magnetometer over the area to see what Oswald might have left behind – a cross; a shrine; a church? At lunchtime we perched on knobbly roots beneath the spreading, if skeletal, canopy of an enormous and ancient pollarded oak . We measured its girth at 26ft 5ins; at roughly an inch of girth per year, that makes it three hundred and some years old. Having been regularly cut at head height, the tree responded by sending out new shoots from its trunk, shoots which had previously lain dormant. This growth branched from the point of pruning, out of the reach of cattle, so it has a magnificent crown. But at three hundred years old it has also been attacked many times by a whole host of enemies and, in response , has produced layer upon layer of the gnarled, crusty burrs which are a tree’s scabs, the scars of its own battles. These make for valuable, beautifully-patterned timber when a tree is eventually felled. But I hope this one keeps going for another couple of hundred years: it’s a magnificent beast. And I couldn’t resist taking its portrait.

Max Adams is the author of The Wisdom of Trees, the perfect gift for nature lovers this christmas.