As greenhouses go, this one is pretty large. Plans have been approved for a 16,000 sq metre biodome, which will recreate the conditions of the Congolese rainforest in England.
The £67m structure, named the Heart of Africa, will be home to gorillas, chimpanzees and okapi, close relations of the giraffe. It will also house various invertebrates and other rare and threatened species.
The building will be bigger than the Eden Project's Tropical House, and will include an underwater feature. When the dome, at Chester Zoo, opens, visitors will be able to step out of the English countryside and into the 80 per cent humidity of a tropical rainforest.
Staff said the experience would be based on a trail through a tropical jungle. "As visitors walk further along the path, the idea is that they encounter more and more of the animals found in the rainforest," said the zoo's development director, Simon Mann.
The display will include mandrills, diana monkeys and pygmy hippos and the water feature will house slender-snouted crocodiles. "There will also be free-flying birds and invertebrates, although they will be in cases, rather than crawling up the trouser-legs of visitors," Mr Mann added.
But Dr Noelle Kumpel, leader of the Zoological Society London's African project, said it would be difficult to accurately recreate the conditions of the Congolese rainforest. "The dome could give visitors an indication," she said, "but the amount of insect life [in the rainforest] is amazing and probably not the kind of thing you would necessarily want to recreate – there are leeches and ticks which can make life hell.
"At times in the rainforest, humidity can reach 100 per cent – it will be difficult to replicate that and to keep visitors unaccustomed to it happy. The sheer diversity will be hard to match. It is possible to walk for miles without seeing a gorilla or a even a chimp in the wild, whereas in the zoo the concentration will be much higher." She added that it would be extremely hard to "conjure up the damp smell" of the Congolese rainforest which, once experienced, "you never forget".
The Zoological Society is running a project in Congo aimed at preserving the okapi, which is often hunted for its skin. Dr Kumpel said the animals are "shy of humans and difficult to survey", but the project could give people a rare chance to see them.
The 34m-high dome, designed by Proctor and Matthews architects, is part of the zoo's larger "Natural Vision" redevelopment, which will eventually cover 50 hectares (124 acres) and cost £225m. The main entrance and car park will be expanded, and a themed hotel and conservation college will be built. The complex is expected to open to the public in 2014, subject to final approval.
The project, which will be built on green-belt land, has been given initial approval by local planners. It now needs the consent of Eric Pickles, the Secretary of State for Communities and Local Government.
However, the Born Free Foundation, a wildlife charity, said it was "sad to see so much" money spent on a "rainforest experience, when the precious, real rainforest remains under threat".
A spokesman said: "The animals to be exhibited in the biodome are unlikely to be reintroduced to the wild. Some might call them ambassadors for their species, but how much are their combined lifetimes in captivity actually worth to conservation?"
As part of a series of developments which will see the construction of a themed hotel and will cost around £225m, Chester Zoo is planning to build a £67m biodome. The complex will house gorillas, chimpanzees and okapi and will cover 1.6 hectares and stand around 130 feet tall. It is expected to open in 2014.
The Eden Project
Cornwall's environmental park has its own set of biodomes, the largest of which – the Tropical Biome – covers 1.5 hectares and is 55 metres high.
The dome houses tropical plants including sugar cane, banana trees and coffee trees, as well as a waterfall and reproduction homesteads. Visitors can also see birds and insects but no larger animals.