On the morning of December 14, 1799 George Washington awoke with a sore throat. His doctors were summoned. By ten o’clock that evening he was dead. It’s unclear what caused his sore throat, but it’s pretty clear what killed him – the treatments administered by his doctors. They removed almost 2.5 litres of his blood through bloodletting (40% of the total amount of blood in his body!), put a powerful chemical in his throat that produced painful blisters, and gave him an enema. All of these treatments were thought to be helpful, but are now known to be completely useless for treating a sore throat.

Over the 200+ years since Washington died medicine has embraced the use of ‘evidence’ to replace ineffective treatments. The discipline of medicine now investigates virtually every aspect of human health, and reports the results widely. The profession of medicine has embraced this knowledge and physicians use it every day for the benefit of their patients. Today medicine is arguably the most powerful profession on earth and makes tremendous contributions to human health and well-being.

Landscape architecture is analogous to medicine where the landscape is the patient, and the landscape architect is the physician. The term “landscape health” is a powerful metaphor for our profession.

But in some ways landscape architecture is more similar to 1799 medicine than current day medicine. Design decisions are often based on opinions or beliefs rather than facts. One belief that turned out to be incorrect had a big impact on Los Angeles. In the 1940s they started experiencing smog and nobody knew what was causing it. It turned out to be caused by several things, but one part of the puzzle was a big surprise. Trees that were planted in the belief that they were part of the solution were actually part of the problem. Research provided indisputable evidence that some species of trees contributed to, rather than reduced, the production of smog.

Part of the reason that landscape architecture is not based more on evidence is that some design issues have very little factual information available upon which to base a decision. But the main reason is that most of the information is only available in scholarly journals that are not readily available to practicing landscape architects. And when the information is available, the key evidence can be very hard to extract because journal articles are written in a scientific manner which is unfamiliar to non-academics.

A few years ago I wrote an article about Evidence-Based Landscape Architecture (EBLA) with a colleague from the University of Guelph, Rob Corry. We published it in one of the top academic journals. It’s three pages long and if you want to read it you can purchase a copy for $41.95. At this price it’s doubtful that it’ll ever be on the New York Times bestseller list. But it’s the reason that I’ve started this blog. There’s a lot of valuable information in the academic literature that could help to transform landscape architecture from opinion- or belief-based to evidence-based.

In our article Rob and I poked fun at different kinds of landscape architects based on a tongue-in-cheek article from the British Medical Journal. You might recognize someone you know! There are those whose practice is “eminence-based” where a person’s status or number of awards transcends evidence. Others are “eloquence-based” where a fancy suit and verbal acuity are more powerful than evidence. And of course there are “expert-based” (not to be confused with expertise-based) practitioners where a person’s reputation for having done lots of similar work is more compelling than evidence. This last one might sound like it doesn’t fit in the list, but consider the cardiac experts who long recommended that heart attack survivors stay in bed for several weeks. Many died during this bed-rest due to blood clots in the lungs. Once the evidence demonstrated that this practice was dangerous the experts changed their advice.

We also proposed a definition in our article: “evidence-based landscape architecture is the deliberate and explicit use of scholarly evidence in making decisions about the use and shaping of land”. Landscape architecture is more than design, so EBLA is more than evidence-based design. Some aspects of landscape architecture already have a strong evidence base – areas like soil drainage, transplanting trees, microclimate modification, materials engineering, and visual preference. In general the physical and biological components have a stronger basis of evidence than social, cultural and aesthetic areas. Academic researchers need to get to work discovering the evidence in these important areas of the profession.

I’m sure there’ll be resistance to the suggestion that EBLA become central to the profession – most likely from eminence-based or expert-based professionals who stand to lose their status. But I suspect that it’ll be embraced by younger practitioners who have recently graduated and have been introduced to process of using evidence as foundations for their designs while in school.

Now the important question – how can you practice EBLA? Our paper suggests a four-step process:

1. Formulate a clear goal or question based on your client’s request;

2. Search for relevant scholarly literature;

3. Evaluate critically the evidence for both validity and usefulness; and

4. Synthesize and apply the findings to the problem at hand.

And if the scholarly literature is too expensive to purchase and too time-consuming to read, either partner with an academic, or read this blog.

One final story about medicine is instructive. Not all that long ago barbers and surgeons were one profession. No kidding – the person who cut your hair was also the person who would cut into your body to remove your appendix or pull out a rotten tooth. The red, white and blue barber’s pole is a throw-back to the days when bloody bandages and blue umbilical cords were apparently wrapped around posts as advertisement. Do you want landscape architecture to follow the path of barbers into providing an important but fairly pedestrian service? Or do you think we should follow surgeons into the realm of respect, credibility and leadership?