The March of the Trees

One of the reasons trees capture my imagination is their potential to be so incredibly long lived and grow so tall. They hold entire communities within their branches and each species presents a different personality. There are so many different trees that have stories and facts associated with them. When I was younger, it was all about what a tree could do for me – the lilac in the garden that I could climb, the sycamore in the street that produced helicopters for me throw and watch in autumn, the weeping willow in the car park I could hide under and play house in, the oak that Robin Hood really used for his meetings (someone should put a ‘disappointment imminent’ warning on the sign at Sherwood Forest which informs you that the claims about Robin Hood’s tree are completely erroneous), the chestnut tree that would provide me with conkers so I could smash the boys conkers to pieces in the playground. But as I grew older, I learned more about the biology of trees and my interest grew to include more about the tree itself.

All the trees in our wood feel special, but there are some that feel particularly so. One of those is the small-leaved lime (Tilia cordata). It’s not a very exciting name, and the species itself is not widespread round Britain anymore. It has heart shaped leaves that are serrated round the edges; there are tiny rusty-orange hairs by the veins on the underside of the leaves, and each leaf can measure up to 8cm by 8cm – smaller than the leaves of the other types of lime found in this country.  The bark is greyish brown, smooth, but with little nobbles on often and sometimes vertical grooves. It’s buds are brown and smooth.

Late last century, Pigott and Huntley¹ wrote a few scientific papers looking at this species.  Small-leaved lime is not a tree I had readily recognised before we owned the wood, but strangely, it is thought once to have been a main constituent of the English woodland.   When small-leaved lime trees were widespread (up to around 8500 BC), the countries climate was warmer than it is now. The species could freely reproduce from seed. But small-leaved limes are sensitive to cold temperatures and frost and as the climate in Britain became cooler, regular production of seed ceased. By 800 BC, the survival of the species had come to depend on the fact the trees were long lived, and on their ability to grow vegetatively (where off-shoots can develop into new individuals). Individual trunks can live for centuries, but the tree as an entity can effectively last forever. Either coppiced, or just collapsing with age, branches regrow from the base of the trunk, and fallen trunks can re-sprout then root along their lengths where they touch the ground, so eventually creating new trees budding from the original. The dispersal of these trees is now limited by how far branches and trunks fall.

So the small-leaved lime trees in our woods are likely to have been growing, genetically unchanged, one part of the tree growing a new shoot or trunk where possible, for thousands of years. And as they grow, fall, re-root down a collapsed branch or trunk, they are slowly ‘walking’ round the wood. What have those trees seen? What an amazing story they could tell. Timeless residents of the wood, immortals living their lives on a timescale impossible to imagine. Each step takes hundreds of years, each breath imperceptible to us as we flicker in and out of existence beneath their branches. What ancient beings lie behind the mundane name of small-leaved lime.

¹C.D.Pigott and Jacqueline.P.Huntley New Phytol. (1978) 81, 429-441
C.D.Pigott and Jacqueline.P.Huntley New Phytol. (1980) 84, 145-164

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