It is Natural England's first State of the Environment report
England is under threat of losing its most precious wildlife to climate change and development, a government advisory body report has warned.
The richness of the countryside has declined dramatically over the past 50 years, and is under increasing pressure, Natural England said.
Butterflies, native reptiles and grassland flowers had all declined over the past half-century, the study found.
It said "landscape-scale" conservation was needed to maintain ecosystems.
Lesser horseshoe bat
The intensive use of both land and sea, along with changes in climate, has seen a 50% decline in woodland butterflies and the loss of rare salt-marsh habitats to rising sea levels, said Natural England in its first State of the Environment report.
But the advisory body also said well-planned conservation projects - such as the re-introduction of the red kite - could be highly successful.
Other species that have fared well include the sand lizard and the lesser horseshoe bat.
But the report said there were concerns as to whether the countryside was "sufficiently resilient and robust, diverse and interconnected" to survive future pressures.
Natural England stressed that a broad and interconnected conservation strategy was needed to bolster England's environment.
The conservation agency recommended reconnecting fragmented wildlife-rich areas, recreating habitats and funding environmentally friendly farming.
Natural England chief executive Helen Phillips said: "We need to find ways to manage our landscape to create a mosaic of uses so that we can help wildlife survive - be it through a new 'national park' around the length of England's coastline, better use of the green belt or improved use of public funding for farmers."
And she warned: "If we don't act, there's a real danger some of our most precious wildlife will be lost forever and our lives will be poorer for it."
In a manifesto written in response to the report, Natural England said it would prioritise storing carbon, absorbing excess water to prevent flooding, and linking up wildlife sites in the use of the public money which it manages.
Environment Secretary Hilary Benn said the group's proposals could make a difference.
Native reptiles such as adders are under threat
He said: "We also now recognise that climate change is presenting us with a new challenge in conserving biodiversity and managing our landscapes.
"We need new approaches to conservation, and we are working closely with Natural England to develop these."
But Friends of the Earth demanded the government take urgent action to protect the environment.
Friends of the Earth England's campaigns co-ordinator Paul de Zylva said: "Ministers must put the environment at the heart of all their policies.
"Including transport, the economy, housing and planning - and invest in the clean, green solutions that would make Britain a world leader in developing a low-carbon economy."