I'm much attracted by the American biologist Edward O. Wilson's hypothesis of biophilia, that humans have an innate tendency to seek connection to nature, for its calming effects.

While most people will be heading for the beach in the next few weeks, I usually head for a national park, to lift my quota of trees, bush, grass and anything else that's green.

This time, however, we're heading for a jungle – otherwise known as Manhattan – to do babysitting duty. Ideally, this means I'd be virtually living in Central Park, but that may be a bit too snowy.

My regular reading of the universities' blogsite, The Conversation, has garnered a fair bit of evidence for biophilia.

According to a survey conducted by the Australian Bureau of Statistics in 2007, each year one in five Australians experiences a mental disorder. Most common are anxiety disorders, such as panic attacks or obsessive-compulsive disorder.

Zoe Myers, an urban design specialist at the University of Western Australia, says research shows that city dwellers have a 20 per cent higher chance of suffering anxiety and an almost 40 per cent greater likelihood of developing depression.

Fortunately, research also shows that people in urban areas who live closest to the greatest green space are significantly less likely to suffer poor mental health.

Myers says more than 40 years of research shows that exposure to nature increases calm and rumination, decreases agitation and aggression, and improves concentration, memory and creative thought.

But it's not emptiness or quiet that has these good effects, she says. "Nature in its messy, wild, loud, diverse, animal-inhabited glory has most impact on restoring a stressed mind to a calm and alert state.

"This provides a more complete sense of 'escape' from the urban world, however brief."

Many studies have attested to the restorative effects of forests but, though holidays in national parks are nice, we need something closer to home.

Melanie Davern, of RMIT University, with colleagues from Melbourne University, say recent research on the benefits of urban greening has found, for instance, lower rates of anti-depressant prescriptions in neighbourhoods close to woodlands in Britain, happier people living in areas with more birdlife, and better health in areas with increased neighbourhood tree coverage in the United States.

Planting trees in parks, gardens or streets has many benefits: cooler cities, slower stormwater run-off, filtering of air pollution, habitat for some animals (such as birds, bats and bees), making people happier and providing shade that encourages more walking.

Professor Pierre Horwitz, of Edith Cowan University, is a great advocate for urban bushland – a bush park of native trees, a wetland, or any native vegetation characteristic of the local region.

"With its undisturbed soils and associated wildlife, urban bushland is more diverse than other types of green spaces in our cities, like parks. The more unfragmented the landscape, or unaltered the bushland, the more likely it will be to retain its biodiversity," Horwitz says.

"Exposure to biodiversity from the air, water, soils, vegetation, wildlife and landscape, and all the microbes associated with them ... enhances our immunity. This is thought to be key to the health benefits of nature."

Horwitz says we know that wealthier people tend to live in greener suburbs, and that wealthier people tend to be healthier. So is it wealth rather than nature that's doing the good work?

Fortunately, no. Many studies have controlled for wealth but still found direct health benefits from exposure to biodiversity.

The benefits go not just to individuals, but to the wider city. Forests and woodlands clean our urban air by removing particles and absorbing carbon dioxide. This reduces premature death, acute respiratory symptoms and asthma across the city.

As well, urban bushland improves city water. Wetlands and the vegetation around them clean water by filtering, reducing exposure to pollutants carried in groundwater or surface run-off.

And not forgetting that vegetation moderates extremes of temperature, providing shade when it's hot and less exposure when it's cold, thus reducing heat- or cold-related illnesses.

Trouble is, urban bushland shrinks as new suburbs are developed on the outskirts of our cities. Worse, bigger houses and more high-rise living is causing backyards to be shrinking, too, even though they contribute to our health and our kids' development.

Not to worry. There's a lot of urban roof space, and we're getting more rooftop gardens. Sara Wilkinson and Fiona Orr, of the University of Technology Sydney, studied the use of a rooftop garden at St Vincent's Hospital in Sydney as part of two "horticultural therapy" programs for people recovering from mental illness.

Among the many benefits participants identified were regular connection with others, developing friendships, experiencing enjoyment and restoration of health.

And if you don't have a spare rooftop, you can join the latest trend and install a vertical garden.

Sorry, I'm getting a bit over-excited here. I wonder if "green space" still counts as green when its covered in snow? Hope the apartment we're renting at least has some indoor plants.

Ross Gittins is the Herald's economics editor.