Using pollard trees as 'living walls' to create agroecological structures. A few design ideas

ˬ˯vᐯ˅ˇ⌣ᘁ᥎ᨆ⏝ࡍ⩗   ᨆ  ⌣˘ˬ᥎ᐯᨆ⌣ᘁ⩗ᨆࡍ˯

This post is from Mésange, my weekly ‘popup’ newsletter, from October 2022 to March 2023. < Previous | Next >

As I plan to develop an experimental food forest, I collect ideas and start to experiment on a small scale (on my parents’ land).

Recently, I investigated pollard trees, an ancient farming technique (or, maybe, a branch of land art?).

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Ancient shapes in agroecosystems

Pollarding a tree means pruning its upper branches regularly, for instance, every 1, 5, or 15 years. Because of this treatment, it develops a peculiar shape over the years…

In a way, this practice is a mimicry of what beavers do in nature! Along rivers and lakes, they chop trees that grow again the following year.

Until about a century ago, such pollard trees were very common in bocage landscapes in Europe. This is because they produce a lot of firewood, leaves for animal fodder, can hold vines like grapes, create a microclimate, etc. Interestingly, they also host a high amount of biodiversity, like rare insects1, and they tend to live much longer than other trees.

Sometimes, the trunks of such trees merge, evoking enigmatic silhouettes… It is called ‘trunks inosculation’.

But, I wondered, what about if we plant pollard trees very very close to one another? Would they merge faster?

And, if we plant them very very close, in a row, would they start to create a kind of… living wall?

Could these walls shape agroecological structures — like a living compost bin, a terrace, or an island on a pond?

I haven’t found examples of such living walls. So, I started to imagine them…

A round of trees to make a living compost bin

In autumn, let’s sow some acorns from a nearby forest.

Very very close to one another. Every 10 cm, 5, or even less (4 in, 2)? For instance, say, in a round shape of 120 cm diameter (50 in).

As I described in another article, acorns germinate so easily, making oak easy to propagate.

By already starting to accumulate our compost or our dry toilet within this circle, we bring nutrients, helping the seedlings to grow faster.

Then, let’s wait for a few years.

Once the small trees reach the height we like, say about 90 cm high (35 in), let’s start to trim them, and again, each year. Slowly, their trunks will grow and merge, creating a living compost bin.

Watercolor of a living raised garden bed with walls made from living pollard oaks.

Underground, their roots will create a dense net, preventing nutrients from leaching. And each year, the branches will grow again.

Watercolor of a round of pollard trees planted very close to one another.

Then, in winter, we trim these new branches. As they are just one year old, some manual tools should be enough. A nice harvest to feed a rocket stove or to make shredded wood!

Want to keep a bit of shade? Just forget to trim one of the pollards!

Watercolor of a round of pollared trees planted very close to one another. One of them has not been pruned this year, providing shade.

I already started a similar experiment at my parents’ place (oh, I think I forgot to let them know…!).

A round of trees to make a living raised garden bed

At this point, what about planting a few vegetables in this round? Our compost bin becomes a fertile raised garden bed!

Also, we are not limited to a round shape. It could just be any shape.

Watercolor of a different shapes of raised bed garden, seen from above, like round, long, hexagonal, flower shape.

Of course, in summer, the shadow from the new branches might be quite dense for the vegetables.

Thus, we may prefer to choose plants that like shade, like edible ferns, hostas, or even berries. Or, we could plant vines that would use branches as a stake, like grapes or beans. Or, maybe, we could trim a few branches from time to time, to optimize access to light for our vegetables, while protecting them from potential heat waves.

By the way, did you know that young leaves of oak are edible? Thus, the living wall of our raised garden bed is also an edible wall!

A row of trees to make a living terrace

Now, let’s imagine we have a slopy grassland.

We would like to make terraces on it, but we don’t have an excavator and, actually, we are not in such a hurry.

Then, let’s plant oaks again, but this time, in rows following contour lines.

Very very close, say every 10 cm, 5 or even less (4 in, 2).

Then, let’s trim them after a few years when they reach the desired height to make a terrace.

20 cm height? 50 cm? 1.5 m? (8 in, 20, 60?)

Year after year, they will develop as pollards. During strong rains, eroded soil particles will tend to sediment at their bases, slowly transforming our slope into flatter and flatter terraces.

And they will merge into a living wall?

Watercolor showing a row of merged pollard trees, seen from above.

A row of trees to make a swale

What about if our grassland is a bit less steep, or if the soil is rich in clay? Then, might it create swales, that would flood during heavy rains?

Watercolor showing how merged pollard trees following contour lines could create swales.

This way, instead of being lost, water would be invited to stay on the land, saturate the soil, and slowly recharge the aquifer below.

A row of trees to make one edge of a pond

Now, let’s imagine we plant such a row of trees, but along a pond, a river, a channel.

In such soil, always saturated in water, oak may not grow well. Willow, on the contrary, would love it. In addition, it is as easy as oak to propagate, through cuttings, this time.

Watercolor of pollard trees planted very close to one another along a pond to create a wall and support the bank.

Here I preferred to keep one edge of the pond with a soft slope. It feels easier to go in and out, and it provides different depths for different kinds of aquatic plants.

Watercolor of a pond in a grassland, seen from above.

I also tried to implement this on my parents’ land! (oh, I should tell them, by the way…)

Endless possibilities…

These pollards of willow around the pond remind me of pollards of ash, that used to be planted along channels to maintain banks in The Marais Poitevin, in France. They also remind me of chinampas, this farming technique in the valley of Mexico, where willows were also used to secure raised garden islands on the shallow lake.

But, in either case, it does not seem that they planted those trees so close to each other.

The willows also remind me of living fences, where willows are planted quite close to one another, and even weaved, to create fences. In another variation, called pleaching, spontaneous trees of a hedge are also weaved.

For the first time last year, I saw a young pleached hedge in Morvan, France. But the trees were not close enough to appear like a continuous wall.

And, it reminds me of living bridges made in India from rubber fig trees!

Overall, while writing and drawing this article, I realized that there is something called tree shaping, which even includes growing furniture…!

But, in all these examples, there doesn’t seem to be living walls… I wonder, what kind of landscapes living walls could create?

Watercolor of a landscape with living walls made of pollard trees

If you have noticed such agroecological structures somewhere, or if you also want to try, let me know, I would be super interested!

  1. I may write a few more documented articles on pollard trees in the future, as I find them very inspiring! For now, as an example of interesting facts related to pollarding, I found this well-written open-access scientific article from a Czech Republic team. They studied how pollarding can actually help preserve some endangered species. Many insects, for instance, can only leave on sun-exposed hollow trees and do not survive in dense forests. In nature, large herbivores and fires can strongly disturb forests, creating sun-exposed hollow trees. Hence, the authors suggest that pollarding can replace those natural disturbances that have become rare in European forests.

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Lénaïc Pardon
Lénaïc Pardon

I am a kind of researcher-explorer. I am French, introverted, and hypersensitive. I value a lot freedom, creativity, and altruism. I am curious about almost anything, but I do have a preference for topics around simple living: permaculture, nature, craftsmanship, autonomy, philosophy, the mysteries of life… More about me and my work >