As cities expand, there's not much street-level space for the greenery. Green walls, green elevated road edges, as well as green roofs can make the city more attractive and healthy. Zhang Qian reports.

Green space and living things are essential for better cities and better lives, but as cities grow bigger and higher and populations increase, there's less and less space left for green.

The outlook for street-level green space might look grim, but there are ways to utilize other spaces to create greenery, as demonstrated by numerous Expo pavilions.

More than 80 percent of the 240 structures use large-scale greenery in rooftop gardens, green-walled exteriors, green interior walls and various kinds of interior gardens.

The greenery not only provides a beautiful landscape but purifies the air, insulates and adjusts the indoor temperature and thus saves energy.

Singapore Pavilion

Hanging gardens and green walls are used in the city-state of Singapore, and in its Expo pavilion.

Singapore, a vertical city, creates a lot of green space in very limited territory in this way. This provides attractive leisure spaces for citizens, helps control the temperature outdoors and inside the buildings and saves energy for the green-walled buildings.

The top of the pavilion demonstrates the scenery of the "Garden City," Singapore's Expo theme. More than 100 kinds of tropical plants, including 20 kinds of orchids, create a tropical oasis.

There are musical fountains, palms, ferns and exotic flowers. A spraying and watering system helps create an imaginary world of music and floral scent. Short-blooming orchids are rotated every month.

The rooftop vegetation reduces the indoor temperature in hot weather. It promotes air circulation along the gradual slope connecting the second floor with the roof.

New Zealand Pavilion

The island nation is famous for its spectacular scenery and greatly varied vegetation, and the New Zealand pavilion has created a mini-park on its sloping roof.

Plants range from plateau vegetation in volcanic areas to tree ferns from lush forests and desert plants from dry areas, as well as vegetables.

A mini "hot spring" with bubbling water and mist is part of the thermal spring scenery. Elsewhere arbors are made with Maori weaving and subtropical plants in a distinctive South Pacific expression in gardening.

Organic vegetables are grown and will be picked when ripe and used as ingredients for the pavilion's VIP kitchen.

A giant pohutukawa with bright crimson flowers stands at the end of a path. It usually blooms in December and is called New Zealand's Christmas tree.

Shanghai Pavilion

Vegetation covers most of the walls and roofs of Shanghai Pavilion in the Urban Best Practices Area in Zone E of the Puxi site.

The walls and roof largely protect the building from direct sun and the indoor temperature is around 5 degrees Celsius lower than the outside temperature - this is achieved without air-conditioners.

Energy consumption is reduced by around 209 percent accordingly, according to pavilion staff.

The exterior western wall is totally covered with plants because it is always exposed to strong afternoon sun.

Instead of planting fixed greenery on walls as in many other pavilions, the Shanghai planners use dozens of movable green panels that can be replaced when the greenery withers or dies.

The green walls also filter the rain water, which flows through the roots and soil in the walls before dropping into the pool on the ground floor.

The water plants in the pool further purify the water and improve the environment.

Theme Pavilion

The Theme Pavilion covers 6,000 square meters in greenery on the eastern and western walls.

The walls each measure 190 meters long by 26.3 meters high each, representing what organizers call "the biggest green wall in the world," twice as big as the wall at the Aichi World Expo in Japan in 2005.

Gardeners chose hardy plants that can endure a hot and wet environment and require minimal maintenance. They include photinia, glossy privet, honeysuckle, abelia and China star jasmine.

It is estimated that the 6,000 square meters of green help retain 870 tons of dust, sequester 3,175 tons of carbon, reduce 96 tons of carbon dioxide emission and save 125,000kwh electricity for air-conditioning annually.

The techniques used to build the green roof in the Theme Pavilion are developed by local experts, suited to the local environment and cost much less than imported systems.

It only costs 800-1,000 yuan per square meter, with an automatic drip irrigation watering system.

Other pavilions

Switzerland Pavilion: It features a 4,000-square-meter rooftop lawn and exhibits Swiss country scenery.

India Pavilion: The dome of the pavilion is covered by grasses and flowers of different colors, creating a splendid "tree of life."

Luxembourg Pavilion: The relatively small stainless steel structure is decorated with beautiful flowering plants and vines, sending the message of "small is beautiful."

Hong Kong Pavilion: Visitors can travel through rooftop woods comprised of 40 trees, such like banyan and osmanthus.

Benefits of rooftop greenery

Reduces dust in the air - Roofs with greenery help reduce dust in the air in the area (estimates 4-28 percent), and kill germs (estimates 2-59 percent).

A one-square-meter lawn can remove 0.2kg of suspended particulates annually.

Produces oxygen - 1.5 square meters of herbaceous plant on a roof can help.

Reduce noise - The soil on the roof helps block low-frequency noise while vegetation helps block high-frequency noise.

Adds humidity and improves drainage - Rooftop greenery can add 6-15 percent humidity to the air and vegetation can help prevent runoff on rainy days, reducing demands on the drainage system.

Adjusts indoor temperature - A green roof can help lower indoor temperature by 3-5 degrees Centigrade in hot weather, saving energy for cooling by 20 percent.

Extends roof life - Roof greenery can help prolong the life of a roof by around 20 years.