Increasing tree cover may be like a ‘superfood’ for community mental health



Imagine Hyde Park in Sydney without its tree cover … the impact on this space and the many people who spend time in it would be profound.
EA Given/Shutterstock

Thomas Astell-Burt, University of Wollongong and Xiaoqi Feng, University of Wollongong

Increasing tree canopy and green cover across Greater Sydney and increasing the proportion of homes in urban areas within 10 minutes’ walk of quality green, open and public space are among the New South Wales premier’s new priorities. Cities around Australia have similar goals. In our latest study, we asked if more of any green space will do? Or does the type of green space matter for our mental health?

Our results suggest the type of green space does matter. Adults with 30% or more of their neighbourhood covered in some form of tree canopy had 31% lower odds of developing psychological distress. The same amount of tree cover was linked to 33% lower odds of developing fair to poor general health.

We also found poorer mental and general health among adults in areas with higher percentages of bare grass nearby, but there’s likely more to that than meets the eye.




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Treed neighbourhoods have a natural appeal to people.
Tim Gouw/Unsplash

How did we do the research?

Our research involved tracking changes in health over an average of about six years, for around 46,000 adults aged 45 years or older, living in Sydney, Newcastle or Wollongong. We examined health in relation to different types of green space available within a 1.6 kilometre (1 mile) walk from home.

Our method helped to guard against competing explanations for our results, such as differences in income, education, relationship status, sex, and age. We also restricted the sample to adults who did not move home, because it is plausible that people who are already healthier (for instance because they are more physically active) move into areas with more green space.

So is the answer simply more trees and less grass? Not exactly. Let’s get into the weeds.




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Trees make it cool to walk

Imagine you’re walking down a typical street on a summer’s day in the middle of an Australian city. It’s full of right angles, grey or dark hard surfaces, glass structures, and innumerable advertisements competing for your attention. Then you turn a corner and your gaze is drawn upwards to a majestic tree canopy exploding with a vivid array of greens for as far as you can see.

A tree-lined street like Swanston Street in Melbourne is a more walkable street.
kittis/Shutterstock

Let’s get the obvious out of the way. Walking down this green street, you may instantly feel some relief from the summer heat.

Studies are linking high temperatures with heat exhaustion and mental health impacts. Research has suggested trees, rather than other forms of green space, may be best at reducing temperatures in cities. It may also simply be more comfortable to walk outside in cooler temperatures – not to mention going for a run or bike ride, both of which are good for mental health.




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Feeling restored and alert

But as the minutes of walking beneath this natural umbrella of lush foliage accumulate, other things are happening too. The vibrant colours, natural shapes and textures, fresh aromas, and rustling of leaves in the breeze all provide you with effortless distraction and relief from whatever it was you might have been thinking about, or even stressing over.

Trees can provide a soothing sensory distraction from our troubles.
Jake Ingle/Unsplash

Studies back this up. Walks through green space have been shown to reduce blood pressure, improve mental acuity, boost memory recall, and reduce feelings of anxiety. The Japanese have a name for this type of experience: shinrin-yoku.

Friends, old and new

You walk past groups of people on the footpath taking time to catch up over coffee in the shade. Some research has found that tree cover, rather than green space more generally, is a predictor of social capital. Social capital, according to Robert Putnam, refers to the “social networks and the associated norms of reciprocity and trustworthiness” that may have important influences on our life chances and health.

Dogs and trees both contribute to building healthy social relations.
Liubov Ilchuk/Unsplash

You walk further and a chorus of birdsong soars through the neighbourhood noise. Trees provide shelter and food for a variety of animals. Research suggests tree canopy tends to be more biodiverse than low-lying vegetation.

Increased biodiversity may support better mental health by enhancing the restorative experience and also via the immunoregulatory benefits of microbial “Old Friends” – microorganisms that helped shape our immune systems but which have been largely eliminated from our urban environments.

Green spaces with tree canopy are settings where communities can come together to watch birds and other animals, which can also be catalysts for new conversations and developing feelings of community belonging in the neighbourhoods where we live … just ask dog owners.




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So, what about the grass?

Our research did not show a mental health benefit from more bare grassed areas. This does not mean grass is bad for mental health.

Previous research suggests adults are less likely to wander in green spaces that are relatively plain and lacking in a variety of features or amenities.
This may also be partly attributable to preferences for green spaces with more complex vegetation, such as parks that mix grass with tree canopy.

Parks with a variety of vegetation, including trees and grass, may be more attractive for a wider range of outdoor activities than those with few trees.
Author

Furthermore, large areas of bare grass in cities can make built environments more spread-out and less dense. Without tree canopy to shield from the midday sun, this may increase the likelihood of people using cars for short trips instead of walking through a park or along a footpath. The result is missed opportunities for physical activity, mental restoration, and impromptu chats with neighbours. Previous work in the United States suggests this might be why higher death rates were found in greener American cities.

Grassed areas can occupy a large amount of space for surprisingly little mental health benefit.
chuttersnap/Unsplash

Large open areas of grass can be awesome for physical activity and sport, but let’s make sure there is also plenty of tree canopy too, while also thinking about ways to get more people outdoors in green spaces. Here are some suggestions.

Making Australia greener and healthier

As the density of Australian cities continues to increase and more of us live in apartments and/or work in high-rise office blocks, it is great to see strategies to invest in tree cover and urban greening more generally across Australia. Cities with such plans include Sydney, Melbourne, Brisbane, Bendigo, Fremantle, and Wollongong.

You can get involved and have some fun at the same time too. Lots of evidence says gardening is really great for your mental health. So why not grab a mate and spend a couple of hours planting a tree on July 28 for National Tree Day!The Conversation

Both the act of planting a tree and its presence over the decades are good for us.
Amy Fry/flickr, CC BY-NC-SA

Thomas Astell-Burt, Professor of Population Health and Environmental Data Science, NHMRC Boosting Dementia Research Leadership Fellow, University of Wollongong and Xiaoqi Feng, Associate Professor of Epidemiology and NHMRC Career Development Fellow, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Logging burns conceal industrial pollution in the name of ‘community safety’



File 20180516 104311 1sl5vdo.jpg?ixlib=rb 1.1
High intensity logging burns and the resulting smoke plume near Mount Baw Baw, April 2018
Photo Chris Taylor., Author provided

Chris Taylor, University of Melbourne and David Lindenmayer, Australian National University

Earlier this year, Melbourne and large areas of Central Victoria, experienced days of smoke haze and poor air quality warnings as a result of planned burns. It’s a regular event occurring every autumn.

This smoke has been reported by both government and media outlets as largely the result of planned burns to reduce bushfire risk, along with agricultural burn-offs and increased use of wood heaters.




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But this is only part of the story. A good proportion of the smoke this autumn has actually come from the intensive burning of debris left behind after clearfell logging. This is essentially industrial pollution.

Smoke Haze over Mooroolbark and Melbourne’s eastern suburbs on Tuesday 1 May 2018, shortly after the time when the Poor Air Quality Index reached 901.
Photo: Chris Taylor, Author provided

Industrial clearfell logging vs fuel reduction

To understand why clearfell logging burns are different compared with planned burns to reduce bushfire risk, we need to understand clearfell logging, which involves cutting most or all of the commercially valued trees in one single operation across a designated area (called a “coupe”).

Large volumes of forest biomass are left on the ground following clearfell logging in the Mount Disappointment State Forest with the Melbourne City Skyline in the background, August 2010.
Photo. Chris Taylor., Author provided

In the process of clearfell logging, understorey vegetation is usually pushed over. Along with tree heads and branches left behind after logging, large volumes of debris – known as “slash” – are created. This is partially removed by applying a high intensity burn across the coupe, which in turn establishes an ash seed bed for the next crop of trees to be established. Generally, around 90-100% of the coupe is burnt.

In contrast, planned burns to reduce bushfire risk (otherwise referred to as fuel reduction burns) are less intense. They mostly target “fine fuels” (vegetation less than 6mm in diameter) on the forest floor and in the understorey, which may average around 15 tonnes per hectare (t/ha). Burn coverage is usually 50-70% of the site.

Surface and understorey ‘fine fuels’ targeted in a recent low intensity burn near Mt Dandenong in April 2018.
Photo: Chris Taylor, Author provided

Clearfell logging burns consume much larger volumes of vegetation biomass in the form of tree heads, branches, bark and downed understorey vegetation. According to a report completed for the National Carbon Accounting System, clearfell logging burns consume, on average, 130 t/ha of slash in mixed-species forest and 140 t/ha of slash in Mountain Ash forests. This means that, while clearfell logging burns cover much less ground than fuel reduction burns, they burn far more biomass per hectare – generating far more smoke.

The list of planned burns on Forest Fire Management Victoria’s website showed that, at the beginning of May, 77 of the 119 burns either lit or planned to be lit across the Central Highlands of Victoria and surrounding areas were on logging coupes.




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These burns were individually lit over a period of weeks, with some days predominantly logging burns, others fuel reduction burns. An example when logging burns were prominent occurred on April 20 this year, where 10 out of 12 planned burns were observed as occurring on logging coupes. Using a simple calculation based on average biomass consumption, fuel loads and burn coverage for logging and fuel reduction burns, we estimate that up to 99% of biomass burnt most likely occurred on logging coupes. The following day, the Environmental Protection Authority observed “poor” air quality at multiple air monitoring stations across Melbourne due to smoke.

MODIS Rapid Response Terra Satellite image taken 20 April 2018 showing the smoke intensity of the logging burns.
NASA 2018

Even on days when the majority of burns lit were for fuel reduction, planned logging burns still contributed a proportion of biomass burned. For example, on April 30, only three out of 12 planned burns were observed as occurring on logging coupes, but they may have contributed to around one-third of the total biomass burned.




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Likewise, on the following day, the Environmental Protection Authority observed “very poor” air quality across multiple air monitoring stations. While multiple planned burns contributed to this pollution event, we contend that logging burns increased the levels of pollution in addition to the smoke originating from fuel reduction burns.

MODIS Rapid Response Terra Satellite image taken 30 April 2018 showing the smoke intensity of the planned burns.
NASA 2018

The key issue here is that not all “planned burns” are equivalent. Fuel reduction burns are intended to reduce the bushfire risk to lives and property. Indeed, work led by The Australian National University shows that regular fuel reduction burns can reduce risk to properties if carried out within close proximity.

In contrast, clearfell logging burns are part of an industrial process that extracts pulp logs and sawlogs for commercial sale to private enterprise. They play no part in reducing bushfire risk to life and property. Actually, the reverse is true: logging makes forests more prone to subsequent high-severity crown-consuming fires with associated risks to communities.




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Victoria’s logged landscapes are at increased risk of bushfire


Given that a substantial proportion of the recent smoke over Melbourne and surrounding regional Victoria likely originated from logging burns, could that smoke be deemed industrial pollution? This is a valid question, given the serious health impacts associated with smoke pollution.

The ConversationLogging burns would not be needed (and a substantial amount of associated smoke not generated) if the forest had not been logged in the first place. It is imperative that government departments inform the public about the smoke pollution coming from logging operations, whose purpose is for private commercial gain.

Chris Taylor, Researcher, University of Melbourne and David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University

This article was originally published on The Conversation. Read the original article.