I spent 32 years working as an NHS doctor, the last 18 of them in intensive care. In that time I saw thousands of patients at their most vulnerable — bodies under extreme physiological stress, bodily systems pushed to their limits. I learned, in the most direct way possible, what stress and illness does to the human body.

What I didn’t anticipate was that retirement would lead me to trees. Or that the science of trees and human health would turn out to be one of the most compelling bodies of evidence I’ve encountered in my career.

A view that changed medicine

In 1984, an American researcher called Roger Ulrich published a paper in the journal Science that was, in retrospect, quietly remarkable. He compared surgical patients whose hospital windows looked out onto trees with patients whose windows faced a brick wall. The tree-view patients recovered faster, spent fewer days in hospital, required less pain medication, and reported fewer negative comments in nursing notes.

It was a modest study in size. But it was methodologically robust, and it asked a question nobody had thought to ask seriously before: does what we see affect how we heal? The answer, it turned out, was yes.

What happens in the body

The decades of research that followed Ulrich’s work have helped us understand some of the mechanisms involved. When people are exposed to natural environments — and this includes simply viewing trees from a window or sitting in a garden — there is measurable evidence of reduced cortisol, the body’s primary stress hormone. Blood pressure tends to fall. There are changes in the activity of brain regions associated with rumination — the repetitive, threat-focused thinking that underlies much anxiety and depression.

The autonomic nervous system appears to shift toward parasympathetic dominance — what we colloquially call “rest and digest” rather than “fight or flight.” These are not trivial effects. Chronic activation of the stress response is implicated in cardiovascular disease, immune dysfunction, poor sleep, mental illness and many chronic disorders.

 

Researchers in attention restoration theory — developed by Rachel and Stephen Kaplan — have proposed that natural environments engage a different, less effortful mode of attention than urban or built environments, allowing the directed attention systems we use for work and problem-solving to recover. This may partly explain why time near trees tends to feel restorative in a way that is difficult to achieve through conventional rest alone.

This is not about deep forest

One of the most important practical points in this literature is that you do not need to be immersed in ancient woodland to benefit. Studies have demonstrated measurable physiological effects from urban trees, garden trees, and even views of greenery through windows. This matters enormously in the UK context, where dense forest is not the norm and where most people live in towns and cities.

The implication is straightforward: trees in streets, gardens, parks, and hospital grounds are not aesthetic luxuries. They are health infrastructure.

The wider picture

The UK has some of the lowest tree canopy cover in Europe. We also have a mental health crisis of significant scale, with demand for NHS mental health services consistently outstripping supply. I am not suggesting trees are a solution to complex systemic problems. But I am suggesting, on the basis of a substantial and growing body of evidence, that they are part of the answer — and that we consistently undervalue them.

As a clinician, I was trained to look for interventions that are effective, safe, cost effective and scalable. Trees meet all three criteria. They are also, in most cases, permanent — a planted tree continues to deliver benefits for decades and often centuries.

That is an extraordinary return on investment. And it is why, after 32 years in medicine, I now grow, nurture and love trees.

Paul is a retired NHS consultant intensivist and the founder of Trees with Love, a specialist tree nursery in Wales growing native, ornamental, and premium trees for gardens, landscapes, and habitat creation.