Why are trees good for us?

How trees affect our mental and physical health is becoming increasingly well documented – but this article asks the deeper question of why?

It began with knowledge that trees take the carbon dioxide that we breathe out and convert it to oxygen as part of their own respiration. Trees ‘clean’ air for us to breathe – every child is taught this. Building upon this fundamental idea – ‘trees are good for us’, cutting edge research is minutely examining how everything from the chemicals that trees emit to the light waves filtered through green leaves has a measurable positive impact upon human health. As these investigations march on we discover an understanding of the richness of wellbeing available to people from just being in the presence of trees; stress and anxiety reduction, increasing memory, lowering of cortisol and blood pressure. We know that people who live in close proximity to trees live longer and healthier lives. These discoveries go well beyond the concept that trees are an important part of our healthy ecosystem and climate management for us to thrive. But answering the ‘how’ does not answer the ‘why’.

Below the waterline of our cognitive awareness is a more primitive, evolutionary context that has shaped our reactions to stimuli over millions of years. These primitive pathways belong deep in our evolutionary ancestry and may point to the, as yet, unanswered question of ‘why are trees good for us?’

We came from trees.

Take the most obvious human features – our forward facing eyes, or even our dexterous hands and opposable thumbs. Why do we have these? Because of angiosperms – Flowering, fruiting and seeding plants. Paleobotanical research has identified a major evolutionary event with the development of angiosperms and their corresponding dispersal agents during the Eocene period of our planet’s evolution. In other words 50-60 million years ago plants developed new methods to disperse their seeds to further than the wind alone could carry them. Trees and plants evolved sweet, juicy outer cases for their seeds and placed on the terminal branches of the newly evolved angiosperm. This resulted in corresponding morphological co-evolutionary interactions with primates, bats, and plant feeding birds. So successful was this symbiosis that the plants that displayed these traits survived to reproduce, and the animals and birds that survived were the ones who were able to benefit from these adaptations. All evolved around the provision of the fruit provided by plants and trees.

A key reason that we look as we do has alot to do with trees.

Our evolving ancestors eventually came down from the trees over 50 million years later – but crucially only 10% of our primate evolution has since been as a ground dweller and not a tree dweller. Hence our co-evolutionary lives: of trees and of man still have a dominant effect. Even if we don’t see it now.

Our millions of years in and with the trees means that aspects of their wellbeing and our wellbeing are inextricably linked. Why do trees hold the secret to our health – because they shaped us into the mammals that we are today. We thrived in an environment provided by trees.

So the next time you ponder why the same chemicals, phytoncides, emitted by trees as part of their protective immune system also boosts ours then ‘taking the airs of the forest’ might just make a bit more sense.

Sosen, Mori (Japanese, 1747–1821) Monkeys in a chestnut tree

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