Right now, I am writing the biography of a thousand-year-old oak tree. It is a little-known fact that there are more thousand-year-old oaks in Britain than in the whole of the rest of Europe put together. These trees are the ne plus ultra of botanical life on these islands, unique ecosystems of illimitable importance. I want to find out what kind of ecosystem services an oak contributes over this kind of time span. How much carbon does the tree drink from the heavens and sequester in biomass over a millennium? How many litres of oxygen does it pump out into the atmosphere, for us to breathe, over 12,000 months? How many tonnes of leaves and acorns fall to the ground, to feed mammals, decompose, fertilise the earth and grow the oak woods of the future? How many hundreds of species inhabit the oak through the stages of its life? Also, significantly, I want to consider how these trees have nurtured us, culturally and socially, when forty generations of humans have passed under them, pausing to tryst, worship, proselytize, muster courage, grieve and die.