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With National Tree Day coming up on Sunday 29 July, new research on how urban greenery can help mental health shows why it might be a good idea to get out there and plant a tree.

Adding greenery to vacant urban land significantly reduces feelings of depression and improves overall mental health for nearby residents.

These are the findings of a study published in the Journal of the American Medical Association this month, based on a three-year study where vacant plots of land were cleaned up, graded and covered in grass and a small number of trees. The plots were then given a low wooden perimeter fence and provided with monthly maintenance.

Researchers from the University of Pennsylvania found that people living near the green lots had a 41.5 per cent decrease in feelings of depression compared to those who lived near lots that had not been cleaned up and greened. Those living near green lots also experienced an almost 63 percent decrease in self-reported poor mental health compared with those living near lots that received no intervention.

Lead author Dr Eugenia South said targeting dilapidated land could be an effective, low-cost tool for local councils to help address mental health problems, particularly for US cities where 15 per cent of land is deemed vacant, and much of it blighted or containing dumped waste.

“Dilapidated and vacant spaces are factors that put residents at an increased risk of depression and stress, and may explain why socioeconomic disparities in mental illness persist,” Dr South said.

“What these new data show us is that making structural changes, like greening lots, has a positive impact on the health of those living in these neighbourhoods. And that it can be achieved in a cost-effective and scalable way.”

The study involved 541 lots, with some greened, some just removed of rubbish and some left untouched. Those that were cleaned but not greened showed no significant change in mental health outcomes. Those greened areas in low socioeconomic areas were associated with stronger than average reductions in reported depression.

“The findings support that exposure to more natural environments can be part of restoring mental health, particularly for people living in stressful and chaotic urban environments,” co-author Dr John MacDonald said.

The cost to transform a vacant lot was about US$1600 (AU$2147), and US$180 (AU$242) a month to maintain.

“This study extends previous work showing a clear association between green space and mental illness by demonstrating that adding green space to people’s neighbourhood environment can improve the trajectory of their mental health,” the research paper said.

Green space good for older people too

The study joins a gamut of literature on the benefits of greenery for mental health.

Another study published in Environmental Health Perspectives earlier this month found green space was associated with slower cognitive decline in older people.

Tracking cognitive ability in 6500 people in the UK over a 10-year period, researchers found slower decline in verbal and mathematical reasoning, verbal fluency and short-term memory in those living in greener areas.

“Our data show that the decline in the cognitive score after the 10-years follow up was 4.6 per cent smaller in participants living in greener neighbourhoods,” Barcelona Institute for Global Health researcher Carmen de Keijzer said.

Co-author Payam Dadvand said the findings were important as the world’s proportion of people aged over 60 was predicted to double between 2015 and 2050, with the incidence of dementia also expected to grow at a similar pace.

“Although the differences in cognitive decline observed in our study are modest at individual level, they become much more significant if we consider these findings at population level,” Dr  Dadvand said.

“If confirmed by future studies, our results may provide an evidence base for implementing targeted interventions aimed at decelerating cognitive decline in older adults residing in urban areas and hence improving their quality of life.”

Research has also shown greenery can help boost learning outcomes in children.

And there’s strong evidence that greenery and views of nature improve the effectiveness of office workers.

See how you can help green your community on National Tree Day here.

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