Root and Branch

Writer and rewilding campaigner, Gordon Eaglesham, explores the astonishing natural history of the magical oak tree. First published in the November issue of Think Like A Mountain. For more information see Scotland: The Big Picture

Few species demonstrate the inter-connectedness of nature better than the oak. A single tree can create and support an entire mini-ecosystem for centuries. A recent study of Britain’s two native oak species, the pedunculate and sessile, found no less than 2,300 species connected in some way to them, with many dependent on these majestic ‘wildlife reserves’ for food and shelter. For some creatures, the tree is their sole habitat. To explore these interactions and the oak’s countless nooks and crannies is to enter a hidden world.

In the oak’s remarkably intricate network of roots, a symbiotic relationship with a variety of fungi unfolds. The fungi receive sugars and carbohydrates from the tree, and the tree gains nutrients and minerals in return. An accumulation of the oak’s soft leaf litter provides the ideal conditions for toadstools such as oakbug milkcap, to flourish in autumn. They, in turn, provide sustenance for species such as bank voles, wood mice and the common shrew, that spend much of their time nibbling away under the decaying foliage. Fungi provide a valuable lifeline during harsh winters.

The oak woodlands of Taynish in Argyll are one of Scotland’s finest remaining fragments of a forest which once fringed much of the west coast.

Falling acorns in autumn provide another bounty for badger, deer, wild boar, red squirrel, and jay. The latter is instrumental in expanding the tree’s distribution, often flying up to a mile with these perfectly formed carriers of life, before caching them. They do this with such frequency they often forget some of their buried treasure and these begin to germinate and grow, safe from hungry mouths and the shade of large trees.

Climb the fissured bark in mid-summer, and you may come across the caterpillars of purple hairstreak butterflies feasting on the flower and leaf buds. Should you ascend further into the maze of trunk crevices, there are avian residents including, marsh tit, treecreeper, nuthatch and pied flycatcher, concealed in readymade nest chambers. Or perhaps there will be one of a dozen bat species known to favour vacated woodpecker holes. There are 1178
invertebrate species hosted by oak, and the tree’s all-you-can-eat buffets are highly-sought spots, particularly in the canopy.

The canopy is also the place for a profusion of lichens, squirrel’s dreys, buzzard or sparrowhawk’s nests. Descending back into the shade of the field layer among wildflowers an array of ferns can be found. These are a reminder that temperate rainforest previously cloaked much of the west coast of our country. Closer to the ground level is the territory
of mosses and liverworts. These ancient epiphytes grow and reproduce over decades on the trunk and branches of these long-lived leviathans. Between here and the woodland floor there will be a fascinating assortment of insect life, including beetles, moths, spiders and millipedes.

Moss covered oak trees. Image credit Scotland: the Big Picture

Indeed, the oak’s decaying timbers are vital for countless invertebrate species. Complete lifecycles are played out on and around the tree; from a tiny egg in the bark crevice to pupation in the fertile leaf litter. Oak trees provide refuges and breeding sites up and down their sturdy frame. The nutrient-rich soil also provides ideal growing conditions for plants such as wild garlic, primrose, wood anemone, wood sorrel and bluebell. But perhaps the most surprising
beneficiary of the mighty oak is the otter. It may often take advantage of the oak’s expansive root system latticing a riverbank for these provide perfect hollows for holt sites.

This is merely a snapshot of the intricate web of life that exists in and around an oak. Ancient, enormous, sprawling oaks, or indeed their smaller counterparts clinging to thin soils on the Atlantic edge, create a vibrant ecology. It’s something we cannot easily replicate. Oaks great and small provide a complex food chain stretching from the roots to the highest branches. Acorns, leaf litter and foliage support small rodents, invertebrates and grazing animals, which in
turn, sustain small birds and larger predators. And underpinning everything is that magical mulch of decaying
wood, soil and fungi that creates the ideal conditions for all of this life to develop.

It takes a long time. So, the next time you pass an oak, don’t take it for granted. Stop and take a closer look. Who knows what you’ll find.

Featured image shows one of the newly planted oak trees in Glen Rosa in its protective tube. Photo credit to Arran Ranger Service.