Nearly half of England's traditional orchards are in a neglected condition, a study of aerial photographs suggests.
Some 35,378 orchards - home to wide varieties of apples and pears, as well as wildlife - were identified by the People's Trust for Endangered Species.
Researchers say 9% are in pristine condition, 46% were in a good state and 45% were in a poor condition.
The five-year project aims to map sites that are in decline to provide a basis for future work to protect them.
The trust said traditional orchards were increasingly at risk because of neglect, intensification of agriculture and pressure from land development.
Anita Burrough, orchard officer for the trust, said: "The mosaic of habitats that comprise a traditional orchard provide food and shelter for at least 1,800 species of wildlife, including the rare noble chafer beetle which relies on the decaying wood of old fruit trees.
"With this loss of habitat, we also face losing rare English fruit varieties, traditions, customs and knowledge, in addition to the genetic diversity represented by the hundreds of species that are associated with traditional orchards."
'Biodiversity hot spots'
The first ever survey of orchards from the air started with conservationists from the trust searching photographs. Orchards can be identified because of the planting patterns which sees the trees growing in evenly spaced lines.
A fifth of the orchards discovered were then surveyed by volunteers, to record species, age and condition of the fruit trees.
The trust hopes its work will be used to monitor targets to restore sites, while working with owners to provide advice and inform local planning policies and development.
Traditional orchards - home to apple varieties such as Peasgood's Nonsuch and Sheep's Snout - tend to be cultivated without pesticides and use animals for grazing instead of mowing.
But numbers are said to have declined by 63% since 1950.
Peter Brotherton, head of biodiversity for government agency Natural England, which part funded the study, said: "Traditional orchards can be biodiversity hot spots, but without proper protection and sensitive management, they can easily slip into decline."