Astonishing Ancient Woodland

A PhD researcher from the University of Reading has selected a local Woodland Trust site, to collect some samples for laboratory analysis. She is investigating the crucial link between oak trees and the nutrient exchange facilitated by the tiny mycorrhizal fungus attached to the trees’ roots. As she spends the summer collecting samples across Britain, Matt Parkins reports on her recent visit to Grey Park Wood on Dartmoor. She will returning to East Dartmoor to collect samples under the oaks in Yarner Wood.

PhD researcher, Petra Guy, looking for the ideal spot for a soil sample

When you quietly walk through an ancient oak wood, taking in the lush smells and bustling sights, you may feel entwined in the web of life around you. In the upland woods of Dartmoor, the darting flight of the pied flycatcher, or the percussive rhythm of the great spotted woodpecker, greet you in spring and the buzz of bees and hum of hoverflies build up as summer arrives, culminating with wide, gliding wings of the white admiral and the serenity of the silver washed fritillary. The sparkle of the electric blue, beautiful demoiselle may flutter over a tumbling woodland stream where the dipper darts and perches in search of a wealth of invertebrate aquatic life. But, do you wonder where it all comes from? What is beneath all this complex beauty? What intricate network of life ties it all together?

Petra searching for the mycorrhiza beside a large oak tree

My questions were answered one scorching summer day at Grey Park Wood, an upland broadleaved wood that stands astride a steeply descending tributary of the river Dart. I caught up with Petra Guy, a PhD researcher who was working her way around the country, collecting samples from ancient woodland soil for her study.  Kneeling at the base of a grand sessile oak, she explained the reason for her country-wide quest. “I’m taking up to three samples from each tree. I’m specifically looking for the various mycorrhiza associated with oaks”.

Gently brushing aside a healthy layer of leaf litter she began to search the humus lying beneath, saying that, “This is where you begin to find the roots of the oak. You can see small traces of white fungi along the root and, this is where the nutrient exchange takes place. The tree extracts its nitrogen, phosphorus and other essential elements from the soil in this way; it can’t do it effectively itself. It’s astonishing to think that these mighty oak trees can only feed through this interaction”. These tiny structures of different colours and shapes that transfer food from the soil to the tree are vital to the entire woodland ecosystem.  “Oh, here’s a nice one. It looks like a little yellow coral”. She went on to explain that “This is ectomycorrhiza which is associated with trees. It a symbiotic or ‘obligate’ relationship where the fungi require carbon from the roots. They provide nutrients then receive carbohydrates from the growing tree”.

Top image: A fragment of yellow mycorrhiza, yet to be identified. Bottom: Healthy humus with root filaments and fungal structures

Standing up, Petra began to drive an auger into the soil. “I want to see if there are different species at different depths and I need to ensure that I collect as many types of mycorrhiza as I can to exhaust all the species associated with each tree. I also want to find out if the species change across the country, with soil type and climate.”

“I selected oak as it is such an important woodland tree…”

Gently replacing the moss and leaf litter before moving to the next tree, she took great care to ensure that the next specimen was standing clear of other trees. “I need to make sure I only collect samples from oak. I selected oak as it is such an important woodland tree and is found across the country”. Having been in Surrey and south Wales, she will be heading to north Wales and Scotland next; taking most of the summer to collect her samples. “I’ll freeze these and, when I get back to the lab in September, I’ll do a DNA analysis on each sample of mycorrhiza to identify the species.”

In time it may become an ‘indicator’, a technique for monitoring the health of a woodland. She continued, “This will help us understand how human impacts, like nitrogen deposition and climate change, could be affecting our woodlands and factors that negatively impact our mycorrhizal communities are likely to negatively impact our trees so, it’s vital that we learn more about, and care for, these communities.”

Taking a rest in the shade of the canopy, we reflected on the fascinating complexity of woodland ecosystems and marvelled at the essential, unsung heroes, the tiniest fungal organisms that support the largest and mightiest oaks in the wood. What’s going on in the ancient woodland soil is truly astonishing and the part it plays in the web of life is not to be taken lightly. It’s the small things in the soil beneath our feet that promote the growth of our trees and forests; ectomycorrhiza is a crucial link in the chain of life.

by Matt Parkins

Petra Guy is based in the School of Biological Sciences at the University of Reading under the supervision of Brian Pickles. Her working title for the PhD is “Future Forests and Wild Woods”.

If you want to find out more about the fascinating and crucially important world of ectomycorrhiza, delve into this website.

Grey Park Wood is one of the many Woodland Trust woods around Dartmoor

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