‘A drink in the Royal Oak, with all its richly grained tables and low-hanging beams, may not after all offer a momentary step back into the past, but rather a glimpse of the future.’

—— Fiona Stafford, The Long, Long Life of Trees (2016)

We are now standing right next to an oak tree. What do you think about it?

You're right, it looks quite big—yet rather dead. However, compared to other trees you see along the walk, you can tell that this tree is significantly bigger than others.

This is how ecologists quickly judge the age and formation of a habitat. Along the walk, you mainly see thin trees and the canopy is not fully closed. This means this woodland is rather young (and of course, we know from history that the trees in this woodland are mainly plantation). However, you also see lots of undergrowth (ferns and weeds)—this is usually a sign of natural regeneration, because it would not be possible to plant that diverse biodiversity.

But we see some old oak trees here, actually quite a few. How do we know how old they are? Are they even older than this arboretum?

Height is not usually a good estimator of oaks' age. You will notice oaks branch a lot. In fact, they have very weak apical control, that means, they are not keen to grow taller. They mainly invest in branching out. The better guess would be from the girth of the tree. As tree grows, the woody tissue also grows outward from the tree and forms what we commonly known as tree rings. Tree rings tell a lot!

However, it is unrealistic to cut open a tree just to count the tree rings for knowing its age. The girth is reliable to guess: 1 metre is equivalent to 100 years.

Tree rings are very informative in the tree's life history. They are formed by alternating light and dark bands (the small figure). The dark bands are denser wood as trees grow slower in fall, while the light bands are less dense as trees grow faster in spring and summer. The bands could be thicker in a rainy year as the tree grows more.

<aside> 💡 Using the chart, guess how old the trees are in this Arboretum?

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Oaks may live for 1,000 years. They are fascinating long-lived trees which have been around in the British landscape and overseen many historical events. They are classed as ancient from 400 years onwards.

Ancient oaks have lots of aging characteristics: hallowing in trunk, decay holes, bark loss, dead wood in the canopy, fungal growth. But, but—they also house a great number of interdependent wildlife species.

Credit: Worcestershire Biological Records Centre

In fact, oaks support more life than any other native tree species in the UK. They are host to hundreds of insect species, and thus supplying food to many birds. Their acorns are food to small mammals including squirrels, badgers, and dear. Even their fallen leaves support the invertebrate and fungal diversity in soil. The holes in their tree bark are nesting spots for pied flycatcher, redstart, and marsh tit—rarely you can also find bats.

But their longevity remains a puzzle: we are not so sure yet how they can grow that old. Trees live a sessile lifestyle: they cannot escape from unsuitable environment once they are born. And the environment changes. Department of Plant Sciences and the Blenheim Palace recently establish a new project to resolve this mystery, led by John MacKay and Henry Hung.

Nonetheless, we have to properly manage these old oak trees to maximise their full benefits. One usual important aspect is to reduce the burden for the tree, as its structural support weakens. This can include thinning the tree crown, scaffolding support, and pollarding (removal of the upper branches). These are known as veteran tree management.

This sycamore tree is thinned.