What it says
The tree speaks of connection — roots in earth, branches toward sky, trunk between. It is one of the few symbols found in almost every culture: the Mesopotamian tree of life, Yggdrasil, the Bodhi tree, the sefirotic tree.
It also speaks of duration, on a scale that is not ours. Planting an oak is planting for generations you will not see: it is the one thing we cultivate without being its beneficiary.
What research established
The roots of most forest trees associate with mycorrhizal fungi, which greatly extend their absorbing surface and connect individuals to one another.
Carbon transfers between trees through these networks have been measured. Chemical alarm signals, in response to insect attack, are released into the air and detected by neighbours.
A caution, however: the image of the forest as a solidary organism — the "wood wide web" — is heavily debated. Several recent papers contest the scale and above all the cooperative interpretation of these transfers. The network exists; what it means is another question.
What a tree does to whoever looks at it
Studies on exposure to vegetation show modest but reproducible effects on attention restoration and perceived stress. A view of trees from a window is enough to produce part of the effect.
It is one of the few design interventions whose benefit requires no active participation.
Indoors
A potted tree does not replace a view, but it brings a verticality no object gives. Ficus, olive, kentia depending on available light — and light is the only variable that really decides.
our piece on flower symbolism places the tree among the symbols of memory and transmission.