In the opening of his popular 2015 book, The Hidden Life of Trees, Peter Wohlleben describes coming across what he thought was a moss covered stone in a forest, only to discover after removing the moss that it was actually tree bark. I’ll let Wohlleben describe what happens next:
I took out my pocketknife and carefully scraped away some of the bark until I got down to a greenish layer. Green? This color is found only in chlorophyll, which makes new leaves green; reserves of chlorophyll are also stored in the trunks of living trees. That could mean only one thing this piece of wood was still alive!
Wohlleben is describing here what are commonly called “Living Stumps’. Trees that are still green under their bark and able to keep growing wider as more bark grows, but not grow taller. This is incredible because our understanding of plants requires that they need leaves to produce this chlorophyll/green. So how do these Living Stumps do this? How are they still alive?
As Wohlleben explains, these Living Stumps survive because of connections with other trees. Which is the fundamental point of his book; the common understanding of how trees work is wrong! They function as a community, not individuals. They collaborate, share, and care for each other as much as they compete and struggle against each other.
Some of you might be cringing while reading this, while others are nodding their head knowingly. Wohelleben’s attributing of human characteristics to trees and the science he cites has been the source of many questions and debate. Regardless, as Daniel Immerwahr writes about this dispute in the Guardian, trees are an incredible complex, radically nonhuman thing. Trees are trees but sometimes the best we can do to understand them is to compare them to ourselves.
Current research into Living Stumps suggests they survive because of root ‘grafts’. Two or more trees that grew so close together that they merged into each other, sharing water and nutrients between them. Grafting is a common practice in Orchard Farming (fun fact, most common apples you find in grocery stores, e.g. Red Delicious, come from one tree that has been grafted again and again and again. Most apples are clones!) and Urban Forestry (A lot of street trees are made from two trees – the roots from one and the trunk from another. This allows the street trees to have hardy, disease resistant roots which are required to grow in urban environments).
Grafting can do some counter-intuitive, incredible things. Consider the Tree of 40 Fruit that has branches from 40 different trees grafted together, producing an incredible diversity of fruit and flowers. Or look at the photo below of a two trees that have grafted together that one of them has had its lower half cut away and is still living.
Now two living trees grafted together makes sense. They can share resources. The leaves of one creating carbohydrates that are “traded” for the water and nutrients from the roots of another. But why do living trees support living stumps? What do the living trees get in return? Is supporting the living stumps a ‘selfless’ act?
There are some current theories that trees tap into the stump’s root system and use it as an expanded root system for accessing water and nutrients. Some recent research from Bauder and Leuzinger (2019) supports this, showing how Kauri trees take water/nutrients from living stumps during the day and store it there during the night.
In Pacific Spirit Park we are blessed with a large amount of Living Stumps. These are almost always Douglas-Fir Stumps – which are locally referred to as ‘Douglas-Fir Knees’. This name seems to come from their rounded top looking like a kneecap. Usually they are about knee height as well. However, diversity does abound.
Which brings me to the question I asked in the title. Why are there so many Living Stumps in Pacific Spirit? I’ve walked through a lot of forests in B.C. and I don’t think I’ve ever found so many of them as I do here!
I have a theory! A theory you can see some immediate evidence for if you walk about 30 feet north up Salish Trail from its fork with Imperial Trail. On the East Side of the trail you can see a Living Stump that is in the current process of slowly growing bark over its top.
As you can see from the middle photo, the tree was clearly cut down. Anytime you see a flat surface on a tree or branch, it means it was cut. Try breaking a stick without using a saw or hammer, the end won’t be flat. You can see all the white resin pouring off the stump as well, as the tree frantically tries to defend the uncovered wood from fungus and insects till it can grow it’s protective bark over it.
While there is evidence that Living Stumps do naturally form as trees crack and blow over in windstorms, a cracked tree will have more exposed surface area which makes it easier for invaders to enter and harder for bark to grow over. Most Douglas-Fir Knees seem to grow from human-cut trees, with a flat end that makes it easier for bark to grow over.
This lines up with the history of Pacific Spirit Park, which has seen a lot of logging over its lifetime. My next question would be, how old are these living stumps? There is evidence that Douglas-Fir Knees can live over 200 years. Living Stumps appear to grow very slowly because they aren’t trying to grow into the sun or gain height. Could some of Pacific Spirit’s Living Stumps be ancient, adaptable survivors like the Western Redcedar Branches in the Park that dropped and grew into trees?
Or are these Living Stumps from recent trail-maintenance logging? The Knees do seem to be clustered near the trails rather then deep in the forest. A few decades ago it used to be common practice to log unhealthy trees along trail edges in case they were to fall on someone. Could our Knees be the recent legacy of these?
Next time you walk through the park, keep your eye out for Living Stumps and see if you can figure what their origins are!