Weighing the Evidence on Sunshine in the Landscape

Shady park in Chicago.  Photo credit Victoria Cox.

Shady park in Chicago.  Photo credit Victoria Cox.

Two things landscape architects can do to make outdoor environments healthier for people

You’ve probably heard the statistics about how sunburn can lead to skin cancer. The Skin Cancer Foundation reports on their website skincancer.org that: “One blistering sunburn in childhood or adolescence more than doubles a person's chances of developing melanoma later in life.”  

That sounds terrible, but it’s important to keep in mind that those are relative risks.  What are the actual chances of getting melanoma?  According to Cancer Research UK (cancerresearchuk.org) the absolute risk of getting malignant melanoma each year in the UK is 17 per 100,000 people, or 0.00017.  And the risk of dying from it is 2.5 per 100,000 people (0.000025) or 1 chance in 40,000.  Double that because of sunburn and the number is still very small – 1 in 20,000.

Is the risk real?  Absolutely.  Is it worth being careful not to get a sunburn?  Definitely.  Is it worth staying completely out of the sun at all times?  Maybe not.   

On the other side of the sunshine ledger there is growing evidence of the risks of staying out of the sun.  A person’s body produces vitamin D when exposed to ultraviolet B (UVB) radiation – a part of the solar spectrum.  Vitamin D deficiency has been linked to a wide range of ailments and diseases from depression to hypertension.  The most certain link is with rickets.  It was the search for a cure for rickets that led to the discovery of vitamin D in the 1920s.  Some of the health benefits of having an adequate amount of vitamin D in your body are healthy bones, reduced risk of influenza, reduced risk of diabetes, and reduced risk of several kinds of cancer (prostate, colon, and breast among others).  Other possible health benefits being studied include cardiovascular disease, Alzheimer’s disease, autism, and multiple sclerosis.

Which is more important - staying out of the sun and reducing your changes of developing melanoma, or spending time in the sun generating vitamin D and avoiding a wide range of afflictions?  We don’t yet know, but one study in the USA (Grant et al 2005) estimated that the economic cost of people receiving too much UVB radiation was US$ 6 to 7 billion, while the cost of people not receiving enough UVB and/or vitamin D was US$ 40 to 56 billion per year. 

In the end it’s a personal decision but the issue has important implications for landscape architects.  Outdoor environments should provide people with the opportunity to get enough UVB to produce a healthy amount of vitamin D without getting so much that it increases their risk of developing melanoma. 

Is there a way to quantify the minimum amount of UVB required and a safe maximum amount of UVB?   One of my MLA advisees, Victoria Cox, decided to investigate (Cox 2013).  For her thesis she conducted a pilot study that measured UVB radiation in a school yard in southern Ontario in mid-winter.  We used some tiny but very sophisticated instruments called dosimeters (do sim’ i ters) to measure the amount of UVB radiation children received during typical winter school days.  The children wore the dosimeters on their arms and all day long the instruments tallied up how much UVB they were receiving.  At the end of each test day Victoria collected the dosimeters and downloaded the data. 

What did she find?  The children received only small amounts of UVB and didn’t come close to receiving enough to cause sunburn, even on sunny winter days.  These results were based on a single location and a small number of students so are not universally applicable, but they suggest that further research should be done.

The second part of Victoria’s study was to use the computer model fastRT (Ola Engelson, Norwegian Institute for Air Research) that estimates amount of UVB received under different environmental conditions.  We used fastRT to estimate how long a student would have to spend outdoors on a February day to generate 200 I.U. of vitamin D (considered adequate intake).  On a sunny day it would take 26 minutes and on an overcast day a student could spend the whole day outdoors and not produce 200 I.U.

Next we ran the model in springtime conditions and found that a person could obtain 1000 I.U.  (the recommended daily dose) of vitamin D in only 7 minutes on clear days and 48 minutes under overcast skies.  Then we calculated how long it would take to produce a sunburn.  Throughout the year it would take from 3 to 5 times as long in the sun to get a sunburn as it would to produce 1000 I.U. of vitamin D.

But UVB isn’t the only part of the solar spectrum that affects people.  How do the recommendations that would result from this study compare with advice about solar radiation and thermal comfort (e.g. Brown 2010)?  During summer heatwaves solar radiation can add so much energy to a person’s body that it can lead to heat stroke.  The time of year when we need shade to reduce the possibility of heat stroke is also the time of year when the UVB radiation levels are so high that people can get sufficient vitamin D even in the shade.  During the winter the solar radiation we receive has a lot less UVB in it and a person needs to spend quite a bit more time outdoors to get sufficient vitamin D.  But it also typically takes an even longer time to get a sunburn. 

What’s the bottom line?  There are two simple, straightforward actions that landscape architects can take to both allow people the opportunity to get vitamin D and also maintain thermal comfort and safety.

1. Outdoor environments that are going to be used in summer should provide lots of shade.  This will reduce the amount of UVB that people receive while also helping to keep people cool. 

2. Outdoor areas to be used in the winter should provide lots of opportunity for people to get into the sun.  This can provide them with some UVB to produce vitamin D and will also add some heat to their shivering bodies. 


Brown, R.D. 2010.  Design with Microclimate: The secret to comfortable outdoor space.  Island Press.  Washington, D.C.

Cox. V. S. K. 2013. Exploring Ultraviolet B Radiation in the Landscape.  Master of Landscape Architecture thesis.  University of Guelph.

Grant, W.B., C.F. Garland, and M.F. Holick. 2005. Comparisons of estimated economic burdens due to insufficient solar ultraviolet irradiance and vitamin D and excess solar UV irradiance for the United States. Photochem Photobiol.  81: 1276-86.






Landscape Architects can help Control Lyme Disease: Four things to 'tick' off your list

On a sunny afternoon in May a few years ago my brother-in-law Rob and I paddled our canoe across a northern Saskatchewan lake to a wilderness area.  We set up a temporary campsite, cooked our lunch, photographed wildlife, and paddled back across the lake.  That evening as we were sitting down to dinner my sister-in-law said “what’s that little black dot on your neck?” I tried to remove it, but it was stuck to my skin.  On closer inspection I realized it was a tiny wood tick.  I got a pair of tweezers and pulled it off.  Relief! 

But then the penny dropped.  Maybe I had more ticks.  I pulled off my shirt and sure enough I found a tick in my underarm, then one on my side, and before long I had found twenty-six ticks on my body!  But Rob beat that record with a total of thirty-two ticks on him. 

We had all these ticks on us, yet we hadn’t felt a thing. Fortunately for us, wood ticks (Dermacentor variabilis) don’t transmit Lyme disease.  Yet thousands of people in the US and Canada every year aren’t so fortunate.  The ticks that they encounter are the blacklegged tick (Ixodes scapularis) that can carry the Lyme disease bacterium, Borrelia burgdorferi. According to the Center for Disease Control (CDC) almost 30,000 people are confirmed to have Lyme disease each year, but they estimate that the number of infections is likely 10 times higher than reported - nearly 300,000 new cases per year!  A lot of people apparently don’t get too sick from Lyme disease, but some people get very sick and every year some people die. 

If you don’t have Lyme disease in your area, it might not be long before you do.  The CDC has reported that Lyme disease has spread tremendously over the past fifteen years and they expect that trend to continue.  It’s not clear why, but global climate change might be partly to blame.  Whatever is causing its range to expand… it might soon be appearing in a landscape near you. 

The CDC provides good advice for people on how to avoid coming in contact with the blacklegged tick, but of course not everyone is likely to read and follow the CDCs advice.  That’s where landscape architects can help.  There are things that can be done to minimize the potential for people to come into contact with the ticks that cause Lyme disease. 

A few years ago one of my Master of Landscape Architecture advisees, Sarah Ward, studied Lyme disease in the landscape.  She investigated the ecology of Lyme disease so that she could identify critical interactions between people and the blacklegged tick.  She was able to identify times of year, locations, and landscape conditions where people are most likely to come in contact with ticks.

tick lifecycle.png

It turns out that humans are ‘accidental’ hosts of the blacklegged tick.  Two of its preferred hosts are white-tailed deer (Odocoileus virginianus) and white-footed mice (Peromyscus leucopus).  The ticks can’t move more than about 3 metres on their own, and rely on hosts to carry and disperse them. This is a critical point.  Ticks will tend to occur in habitats that favour their hosts – deciduous woodlands.  But don’t think that removing deer and mice from the landscape will solve anything.  The blacklegged tick is equally willing to feed on at least 27 other mammals and 36 species of birds.  A better approach is to identify where and when the ticks will be looking for a host, and design the environment so that the host is not likely to be a human.

Sarah and I published a paper called “A framework for incorporating the prevention of Lyme disease transmission into the landscape planning and design process” in Landscape and Urban Planning.  You can access it through the journal website but I’ve also put an open-access copy of the paper on the University of Guelph Atrium.  You can download a PDF at:



I’ll summarize four of the key points here. 

1. Blacklegged ticks are extremely sensitive to desiccation so they are found almost exclusively in moist habitats with a minimum of direct sunlight. Path surfaces can be made inhospitable to ticks by constructing them of gravel or other xeric material.

2. Ticks can’t jump and don’t drop out of trees.  They crawl along stems of plants and wait at the tip for a host to come along and then they grab on.  That means that paths should be wide enough to allow people to walk along the path without brushing against adjacent vegetation.

3. Seating should be located at least 3 metres away from dense brush, wooded areas, and heavy groundcovers and should be installed on a bed of gravel or other xeric material.

4. A metre-wide strip of xeric material should be installed between lawns and wooded areas and around play areas and patios. Ticks will tend to avoid these dry barriers.

These are pretty simple things to incorporate into your site-scale designs, and while they won’t eliminate the threat of Lyme disease, they will reduce the potential for people to come into contact with the tick that carries the bacterium.

Our journal article has been cited by many other studies.  Much of the current research is focused on the larger landscape and the results will be of considerable interest for work at the landscape planning scale.  Sarah became more interested in medicine than landscape architecture and studied to become a physician.  She went on to become an orthopaedic surgeon.  Rob and I now tuck our pants into our socks when we walk in natural areas, and check ourselves for ticks when we get home.



Ward, S. E. and R. D. Brown. 2004. A framework for incorporating the prevention of Lyme disease transmission into the landscape planning and design process.  Landscape and Urban Planning 66: 91–106

Landscape Architecture: Good Medicine?

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?


Further reading:

Brown, R.D. and R.C. Corry. 2011. Evidence-Based Landscape Architecture: The Maturing of a Profession.  Landscape and Urban Planning. 100: 327-329.