Revealing the inspiration behind his latest epic, Avatar, legendary filmmaker James Cameron recently described himself as a ''nature geek'', and said modern humans were suffering a degree of ''nature deficit disorder''.

(photo by flickr user andy_carter) It may not be a medically recognised condition, but ''nature deficit disorder'' is a concept gaining traction with childhood and behavioural experts around the world.

Afflicting those in hard, urban environments deprived of nature's randomness and balance, it is a challenge facing cities such as Melbourne, whose children will grow up with rising urban density and pressure for open space.

Just as it inspired Cameron, experts hope an appreciation of the modern ''nature deficit'' can inspire Melbourne's city planners to plot a future with vegetative density amid the urban density.

Fertile as his imagination is, Cameron didn't coin the phrase ''nature deficit disorder''.

That honour belongs to Richard Louv, the American author of the award-winning book Last Child in the Woods.

Compiling research from around the world, Louv's book argued strongly for children to be reintroduced to the wilderness. Suggesting social and developmental benefits from exposure to nature, the book highlighted research claiming that a range of psychological conditions could be mollified, at least partially, by spending more time in the great outdoors.

Australian authorities hold similar views: in a 2007 investigation into playground spaces in Victoria, the state government found that young children ''need exposure'' to natural environments to appreciate the ''complex variations of texture, sound, light, smell, colour and temperature''.

The government report The Good Play Space Guide, highlighted the creative impulses that can be fostered by play with the ''loose parts'' of nature - the leaves, twigs and gumnuts.

''Such play is uniquely satisfying as there is no pressure to conform. Various ability levels and strengths, whether they are physical, imaginative, sensory or social, can be applied to loose natural elements to promote meaningful play,'' the report said.

Vigorous debate over the use of public space has long been part of Melbourne life, as organisers of major international events including the formula one grand prix and the Commonwealth Games have discovered when trying to use the city's parks for their events.

But Louv - speaking to The Age ahead of his visit to Melbourne in April - says it will no longer be enough to preserve the parks we have.

''Conservation alone won't provide the biodiversity we need in the future. To achieve that we need to - as ironic as this sounds - create nature in our yards and our cities,'' he says.

Rethinking the urban park is one of Deakin University expert Mardie Townsend's favourite conversation topics, and one she thinks the nation will be focusing on more often as it evolves towards high-density living.

''We now have a lot more people with little or no backyard, so there's much more pressure on the public parks, and we have to find a way of creating more public parks or more green spaces that people can access,'' she says.

Townsend believes parks need to become more interactive and offer not just trees and grass to visitors but also spaces to cultivate plants.

''Parks that include a gardening element will be really important,'' she says.

Melbourne's inner suburbs already have several community gardens, where locals can lease a plot of dirt to grow vegetables or other plants. Townsend says multiple benefits flow from such places: they offer recreation and encourage healthy eating while tackling the problems of rising food prices and carbon emissions from the transporting of food.

''It has very significant impacts on children's understanding of food - where it comes from and how it's grown - but also their willingness to try new foods, their willingness to eat nutritious food and their engagement with food,'' she says. ''All of this is really important in modern society, where kids are often sitting in front of computers, televisions and not socialising.''

Towns in northern England, such as tiny Todmorden, have already ripped out council flower beds and replaced them with simple crops such as broccoli, encouraging passers-by to harvest vegies at their leisure, free of charge.

But in Melbourne, meddling with parks has always been easier said than done. Yarra Council discovered that last month, when plans to establish a community garden within a park in Princes Hill sparked local anger. One group of locals wanted the space to grow plants, while others saw the move as a reduction of existing park space for the benefit of few.

The passion sparked by the debate caught the council by surprise, and it will come to a head at a council meeting in April.

Mindful of that controversy, and echoing Louv's comments, Townsend says we will need to be creative when scouring the urban environment for places to establish new parks and community gardens. She suggests taking advantage of laneways, disused blocks of land and river frontages that are unsuitable for housing developments.

Longer term, she says, there may be commercial benefits for private companies that turn some of their land into public recreation spaces.

''Think of a place like Chadstone [shopping centre], where they have miles of car-parking and have two or three layers. Why not make the top one a [nature] park, which keeps everything cool under that roof and provides a wonderful open space for people,'' she says.

''People are far more likely to go to Chadstone if there's a nice park there, where they can sit and have their lunch before going in to shop, so it becomes an economic attractor to business.''

In the serious business of playtime, few places are more important for children than school.

In a more congested city, the sports fields, playgrounds and other facilities within schools will be too valuable to be simply locked up after 3pm.

Victorian government policy already encourages schools to open their facilities to local communities outside school hours, welcoming night schools into empty classrooms, and sports clubs on to vacant ovals.

While each school decides for itself the extent to which it opens its gates to the broader public, the idea is to turn schools into ''community hubs'' with greater connection to those living nearby.

In places where social disadvantage coincides with a paucity of parklands, such as Dandenong in Melbourne's south-east, there is an even greater need for schools to take a leadership role, according to Martin Culkin.

Culkin is principal of Dandenong High School and says he wants to see his school enjoyed by community groups at night and on weekends. ''I like to see the facility used; it's not right that a facility that will be a $45 million cost to the taxpayer be locked up at 3.30pm. We will want to see some use of the sporting areas, the gym areas and other areas by the community,'' he says.

While vandalism has forced some schools to limit access to their grounds after hours, Culkin takes the opposite view. ''If you lock a place up, you are asking for trouble. If you allow managed access, you get a better result. You're not going to get a high volume of intruders and people up to no good when you've got activity in a place.''

Finding the space for parks in the decades ahead will be one battle, but keeping those spaces green and usable will be quite another. Melburnians need no reminding of the impact drought has had on their parks and sports fields in recent times. As a drying climate has turned fields to dust, many councils have installed artificial surfaces in recreation spaces, including sand, asphalt and, increasingly, synthetic grass.

While those solutions have had localised success, they don't suit a society wanting to curb urban heat absorption, grow food in parks and combat ''nature deficit disorder''.

Instead of looking to the heavens for rain, the answer to keeping parks green seems to be stirring in the pipes below. Authorities in charge of Melbourne's sewer network have recently conducted a major review of the city's wastewater system, and are writing a strategy for its management in the decades ahead.

A key focus of the strategy, led by Melbourne Water, was to investigate whether the treatment of sewage could be conducted in a less centralised way.

Virtually all Melbourne's sewage and wastewater is pumped long distances to one of two massive treatment plants, one in the west at Werribee and one in the east at Carrum. Despite being treated to very high standards, the vast majority of that water is then simply pumped out to sea.

The recent sewage strategy investigated whether a larger number of small treatment plants could be built around the suburbs - reducing the need to pump the water long distances, and increasing the likelihood that treated water could be re-used locally on parks, gardens and fields.

The strategy ultimately found it could be done - but at a ''significant'' cost.

CSIRO water expert Tony Priestley says ''sewer mining'' is another option, where existing underground sewage pipes are tapped at strategic locations where water is needed above ground.

Once wastewater is tapped, pumped to the surface and treated, it can be used as a reliable water source for parks.

Successful trials have been conducted around Melbourne at places such as the Botanic Gardens, and Priestley says the technology is ready to go. ''But,'' he warns, ''it's bloody expensive. It's basically a matter of having enough money - and what value you put on the parks, gardens and recreation spaces.''

The mythical Navi people - the indigenous tribe portrayed in Avatar - valued nature and their forests above all else. As heroes tend to do in big-budget Hollywood films, they prevailed in the end, protecting their wilderness against the advances of the corporate bad guys.

Good and evil are not so easily cast in the real world, where the good guys might as easily be those creating affordable housing as those protecting parks.

Louv openly declares he is not an architect, nor an urban planner. But as cities such as Melbourne contemplate fitting more people in the same amount of space, he says, ordinary people must make their voices heard in the evolution of their cities - by starting petitions, writing to MPs and attending community meetings.

''Let planners understand how vital it is in a civic blueprint to build or retain natural spaces ... let lawmakers know that natural play areas need to be part of the mix.''