Tree anatomy & nutrition

Trees, magnificent opportunists

​There are around 64,000 known species of trees worldwide, with roughly 9,000 more yet to be identified. Behind this remarkable diversity lie a few common traits: roots, a trunk, a crown, and the same competitive, opportunistic drive for space and height in order to secure their vital resources—light and water.

Over the course of its life, a tree must meet a demanding set of requirements: spreading both underground and skyward in order to feed and grow, while ensuring its stability, its defense against pests, and its reproduction. To achieve this, the tree has developed remarkable mechanisms of reaction and adaptation. Yet it is also a victim of its own immobility: unable to escape threats, whether natural or human in origin.

This is why, in our view, it is so important to better understand how trees function, so that we can adopt the best practices to ensure the longevity of those we use for support—while enjoying, as harmoniously and respectfully as possible, the magic of their branches.

What lies beneath the bark?

• At the center of the trunk lies the pith, the starting point of the tree’s growth.
• Surrounding it is the wood, made up of a central core—the heartwood—and an outer layer known as the sapwood. The heartwood is the oldest part of the tree and no longer contains living cells; it serves only as structural support. The sapwood, by contrast, is the living part of the trunk: it is within this layer that water, drawn up by the roots, circulates and makes its way to the leaves.
• The sapwood is bordered by the cambium, a layer of cells (invisible to the naked eye) specialized in growth. These cells divide inward to form more sapwood and outward to form the phloem.
  
• It is in the phloem, located just beneath the bark, that the sugar-rich sap produced by photosynthesis flows from the leaves to all parts of the tree.
  
• Finally, all these layers are wrapped in the bark, which serves a protective function.
  

Wood serves four main vital functions for the tree: conducting sap, storing reserves, providing mechanical support, and offering protection and defense.

​A closer look at the tree’s nutrition

We all learned this at school: a tree—like all green plants—produces its own food through photosynthesis. Water drawn up by the roots is transported to the leaves, where it combines with CO₂ to synthesize carbohydrates using the energy from sunlight absorbed by the leaves’ chlorophyll.

Everything starts with the roots, and more precisely with the fine root hairs at their tips, which absorb the water and minerals the tree needs. This sap rises to the leaves through a process called transpiration, which occurs at the stomata on the leaf epidermis. The water absorbed by the roots is effectively drawn upward, much like through a straw.

Once enriched with carbohydrates, the sap—or phloem sap—moves back through the phloem of the trunk and branches, and is then distributed through the sapwood to the wood cells via channels known as medullary rays.

Among the challenges a tree may face in its nutrient cycle are the risk of breaking the upward columns of water (due to the formation of an air bubble) and the obstruction of the phloem sap flowing beneath the bark (from animal stripping, girdling, etc.).

​Attachment methods: the tree’s health comes first!

As we mentioned, over the course of their evolution, trees have developed impressive defense and adaptation strategies. Exposed to the wind, they form reaction wood to counter mechanical stresses and gravity. When attacked by pests or fungi, they deploy chemical barriers to contain the affected area. When pruned—either naturally or artificially—or injured, they produce new, stronger wood to cover the wound. These mechanisms are highly effective, but they do not make trees indestructible.
Before undertaking any work on a tree, it is therefore essential to ensure that it is in good health. Next, one must follow the most respectful practices, in other words, those that:

• preserve as much as possible the upward flow of water from the roots and the distribution of phloem sap through the tree, and
• ​minimize potential entry points for pests and fungi.​

​Traditional Methods vs. Garnier Limb Method

It is for these reasons that we have chosen the TABs (Tree Attachment Bolts) Garnier Limb® technique, as the primary way to secure our platforms in trees.

• Unlike trunk-girdling methods using cables or clamping between multiple beams, the attachment bolts largely preserve the phloem and therefore the flow of sugar-rich sap.
• By maintaining a gap between the structure and the trunk, they also allow the tree to continue growing and to heal the “wound” by covering the bolt with new, stronger wood and fresh bark.
• Finally, thanks to the impressive load-bearing capacity of TABs, only a minimal number of penetrations are required to ensure the structure’s stability and durability.

Beyond the pleasure of sharing information on a subject that fascinates us, this brief introduction to how trees function aims to demonstrate that a sustainable method of building at height—both for the structure and for the tree—is possible, provided that one takes the time to study every aspect carefully!

Source: All data and information presented here come from two MOOCs taken on the FUN MOOC platform, in particular the one offered by Marie-Christine Trouy, Senior Lecturer at the University of Lorraine.