Nagotiate root space and activation pruning
After practicing syntropic forest garden in established forest I learn a few things I like to share.
Disturbance is necessary to establish new trees but in an old forest you like to keep the big and strong ones. Let’s look at this. What works and what doesn’t. I’m still in learning process. Disturbance needs to be strong so young trees can not only establish their root system but thrive. After disturbance root space is renegotiated, new and young trees get a chance to establish their root system. To achieve this old trees need to be pruned to the point part of their root system starts dying back. This seems to be a threshold for success. It should take the mother tree 2–5 years to recover its leaf surface.
Also planting trees in a young well established system can be challenging. First I tried to prune mother trees back in spring and again in summer. Mainly maple and ash. Not much foliage remained. Trees also were topped. I got somewhat of a growth pulse but the newly planted (plum trees 2–3 years ago) and mini kiwi (2 years ago) responded little to the pruning of neighboring mother trees. So I decided to cut some of the mother trees to 1 m, others to the ground. They were about 6–8 m high.
This gave much better response. Now mother trees and fruit tree seem to be synchronized and can grow together. Drastic steps like this are only necessary when you plant into established system. When you plant into shrubs like dogwood 3–4 prunings can be necessary in the first year to get sufficient synchronized growth. Keep in mind root system is much bigger than the canopy. With a bit of practice you can distinguish trees by their root.
For example:
* Walnut black fibrous yellowish inside distinct smell
* Ash white greenish
* Maple brown red somewhat brittle
* Spruce red brown scaly resin smell
* Elder white brown thick distinct smell
* Mulberry yellow brown light color fibrous and thick
When you dig planting hole you find roots and can tell where they come from. If multiple trees of same species around you can measure electric resistance from root to trunk and you should be able to find to which tree they belong. The biggest healthiest tree in the area dominates root space. He is responsible for what grows and what doesn’t. Roots can reach 10 to 35 m from the trunk, in extreme case over 50 m.
In good aerated soil roots of all species grow deep. We find spruce roots while digging a well at depth of 9 m. They followed a gravel layer that was well aerated. Spruce is known for its shallow root system usually 20–50 cm.
On soil with bad aeration most species remain on the surface. Surface soil becomes very crowded with roots. This can lead to water and nutrients competition. Shrubs and grasses can struggle in this case. To make deeper soil available to all species plant pioneers known for their ability to penetrate heavy soil and deal with low oxygen level. At my place I use combination of silver willow, black alder, poplar, elm. This combination can break up compaction. Silver willow survive 3 months of flooding and is able to actively aerate soil, at the same time it has some drought tolerance. Black alder is similar.
That was a little root excursion.
Let’s look at a practical example of planting in an established forest.
Benedikt Bösel from Gut & Bösel did exactly that. 3 trials as I remember correctly. Pinus sylvestris monoculture.
* Removal of 30%
* Removal of 60%
* Clearcut
The effects were drastically different.
Removal 30% and 60% are somewhat similar. Growth was medium to low. Slow establishment of new plants.
In the clearcut new growth was explosive.
It’s not about the species but the growth state of the trees. If you have senescent trees you will have this problem. Root space needs to be freed up so new trees can establish. After disturbance root space is renegotiated, new and young trees get a chance to establish their root system.
When you do heavy pruning on large trees it can happen that you have no effect. In my experience growth pulse is not linked to the pruning but to regrowing. Old trees can take a few years to start heavily regrow. Also some stumps can be active in the ground and slow down regrowth for a few years. Not entirely sure but for example: when you cut down large Fagus sylvatica the stump lives on for a few years. On the other hand pine and spruce roots die within months after tree is cut. When root dies mycorrhiza also dies unless there are living trees it is connected to or newly planted trees where it connects.
Mycorrhiza often have multiple host species. Truffle (Tuber aestivum) forms symbiotic relationship with following tree species:
* Tilia linden
* Quercus oak
* Pinus nigra black pine
* Prunus avium cherry
* Sambucus nigra black elder
* Corylus avellana European hazel
* Castanea sativa chestnut
* and more
This ability to colonize very different species enables mycorrhiza to exchange sugar and nutrients between trees. Actively growing trees with young crown mean also high activity in the mycorrhiza network. This should lead to more mushroom fruiting. Mycorrhiza benefit from tree, shrub and herb diversity. If you like to do a deep dive look up Paul Stamets *Mycelium Running* or Suzanne Simard *Mother Tree*.
What I describe here is the wood wide web.
The wood wide web wants to maximize photosynthesis and it benefits from plant diversity. Disturbance is necessary to renegotiate relationships in the root zone.
In a forest I tested time it takes to start regrowing. It is drastically different from species to species:
* Fagus sylvatica senescent 3–6 years
* Tilia ssp. senescent 1 month – 1 year
* Pinus sylvestris senescent 3–8 years
* Fraxinus excelsior senescent 2–3 years
* Salix alba 2 weeks
* Acer pseudoplatanus senescent 2–3 years
Young or actively growing trees respond very quickly, also the slow species above. To respond quickly I believe they need strong annual shoots to continue growth and give a good growth pulse. Sometimes it’s good to do pre-cut to encourage old trees to form new strong shoots so when you do disturbance they can recover quickly.
In old cherry and pear this is particularly important. Otherwise tree can die. So what I usually do is cut a few upward facing branches to break apical dominance and encourage new growth. Cherry particularly struggle to sprout from old wood. What you can do is increase sap pressure, this will help to resprout. To achieve increased sap pressure I leave a stump instead of cutting back to a fork. In this stump sap is trapped and new sprouts are more likely. I do this with upward facing main branches and also reduce upward facing side branches where I want them to resprout. What remains looks like deer antler.
In senescent cherry I take out about 30% of leaf mass to achieve this activation pruning. Afterwards I give the tree 2 years to build new shoots. After 2 years you see where the tree wants to grow. You remove where it didn’t. In this activated state cherry are capable of 3 m growth annually while before they did just a few cm.
When you want regrow on a specific spot you can do a cut there about 2 cm deep half way around. Below the cut buds will wake up and sprout. This because you break apical dominance and increase sap pressure. Apical dominance is due to auxin, a plant hormone produced in the tip transported down to the roots in the phloem. Auxin encourages root growth and keeps buds from sprouting.
Cherry has naturally a very open crown, light is penetrating deep inside the canopy usually to the trunk. If you rejuvenate a cherry keep that in mind. When it starts regrowing you need to thin it otherwise it can shade itself out. Only leaves at the crown surface get enough light. You end up with very bad ratio leaf surface to mass. Sometimes cherry regrow well for a few years but then die due to self-shading or at least end up senescent again. Open crowned species like birch, walnut, poplar, silver willow are more vulnerable than closed canopy trees like beech, maple, elm.
Pre-pruning is recommended for tree species which take long time to resprout due to the species or its senescence. If you climb up the tree and you find strong annual shoots in the inside the tree usually responds well to pruning.
Activation pruning and thinning is something fun to experiment. You can balance a tree towards biomass or fruit production. Strong annual shoots and enough thinning lead to increased fruit yield, quality and size. To learn this principle you can train on shrubs. First year you cut to the ground, second year you do thinning. Depending on the species you will have bumper crop in second, third or fourth year. Thinning is the key and needs to be repeated. A deep dive into that needs to be separate post.
If you can’t prune or long resprouting time is a problem you can also do root pruning around your new plants. We did this at the forest edge with a tractor and a 40 cm blade. The effect was clearly seen within a few months and dramatic after one year when grass became lush and green.
No need to say this stresses old trees severely. In my case trees lost about 25% of roots. We cut about 7 m from trunk.
You need to create an area with roots of young vigorously growing tree. Or at least no living senescent root. Cut off roots or cut down senescent tree are the second best option. But living senescent tree are no option for fast establishment. If that also not option at least do watering system.
You can cut down small groups of 2–4 trees then you have in the center an area with no competing roots of senescent trees. If you cut back roots give your new plants enough space. Old trees can do rapid root growth in loose soil 2–3 m annually. Have this from graveyard gardener who has plenty of experience. He says Taxus baccata does easily 2 m a year. From the book *Understanding Roots*: apple tree can grow down 2.5 m in one year if loose soil is given. Some tropical figs do 6 m aerial roots a year.
Your plant bed and seed nest are very attractive for hungry roots, they can smell it from meters away.
Last words.
With a bit of practice you can tell apart different tree roots. That is very useful skill to develop
Check out Byron Grows on YouTube, he made a video about Gut & Bösel planting trials.