Landscape architects, engineers, horticulturists and arborists are in hot demand as Hong Kong's grand vision of a clean, green world city gets into full swing. The 'greening' of Hong Kong began last year with a pilot scheme involving the planting of 1,000 trees and 250,000 shrubs in Central and Tsim Sha Tsui. Under the government's 'Greening Master Plan' (GMP), the initiative is poised to enter its second phase. The 'urban woodland' is extending across Mong Kok and Yau Ma Tei in Kowloon, and beyond Central to Sheung Wan, Wan Chai and Causeway Bay. This new phase, starting in September, will involve the planting of another 4,200 trees and nearly a million shrubs. Scheduled for completion next year, it is by far the biggest landscaping project undertaken in Hong Kong, covering 11,300 hectares, or the equivalent of 22,000 football pitches. From 2009 to 2011 the 'greening' will next extend across the rest of urban Kowloon, from Lam Tin to Sham Shui Po, and across all of Hong Kong Island. In total, about 20,000 new trees and millions of plants and shrubs will create green gems of shade, colour and vitality. Hundreds of specialists and a small army of supervisors, landscapers and labourers are needed to create the facelift. Every street was being surveyed for opportunities to create 'an oasis of greenery', said Kathy Ng Tze-kwun, a senior landscape architect with the government's Civil Engineering and Development Department. The GMP's transformation of streetscapes is also an effective weapon in Hong Kong's battle against pollution. 'Trees absorb a lot of pollutants and hydrocarbons in the air,' said Johannes Spies, an associate with ACLA, the master planning division of Hyder Consulting and lead consultants for the project. 'They are also important psychologically, reducing stress and anxiety.' Trees and greenery are a natural air-conditioning system, absorbing heat and reducing temperatures. 'If you look at an infrared satellite photo of Tsim Sha Tsui, Kowloon Park is visibly cooler than the surrounding area,' said David Knight, project manager of Hyder Consulting, for the programme. 'Other studies have shown that creating a peaceful, green environment helps people recover more quickly from illness, reduces domestic violence and improves the attention span of students.' Planting trees across urban Hong Kong is not as straightforward as it might seem. 'There are numerous challenges in congested urban areas, such as narrow pavements, overhead signs, underground utilities and pipes, and loading zones,' said Mr Knight. 'We have to survey every street looking for opportunities without obstructing pavements or upsetting people. 'One of the things we look for are weeds growing. They are a good indication that people don't walk much over the spot, and a tree will have a good chance of surviving.' The project has required a huge data collection exercise, with a tailor-made geographic information system linked to mobile computer technology. Extensive public consultation has also been undertaken with local communities and councils. 'We have had a lot of positive feedback. What the public always asks for is colourful flowers, and selecting them is a challenge in itself because they are seasonal,' Mr Spies said. To instil a sense of local identity, districts are even being 'themed' with their own flower and shrub combinations. From Sheung Wan to Causeway Bay, the theme is 'rainbow' colours. In Yau Ma Tei and Mong Kok, the area is sub-divided into coastal scenery, parkland and green kaleidoscope. 'In each district, we are setting the tone for private developers to hopefully follow the local colour themes,' he said. Public consultation, from schools to community forums, had proved vital, added Ms Ng. 'In the past, trees have been vandalised,' she said. 'It is important to convince children, especially, that we are planting trees for them. It is their environment for the future, so it is important that they love them and protect them.' The government is also promoting cooling 'green roof' initiatives, with gardens and greenery on rooftops, and vines climbing the sides of buildings. More than 100 such projects have been completed, including a 'vertical green panel system' at the Eastern Harbour Crossing. Hong Kong didn't really have a choice but to actively promote this concept. Sustainable cities are the future and they have to be green, Mr Spies added.