The National Forest Company is closely monitoring two million ash trees in its woodland for signs of a disease which has devastated the species in Europe.
The Government banned the import of ash on Monday in a bid to halt the spread of ash dieback – or chalara fraxinea.
The fungus has killed 90 per cent of ash trees in Denmark and last week officials confirmed it was spreading through East Anglia.
The National Forest Company manages 200 square miles of woodland in Leicestershire, Derbyshire and Staffordshire.
It welcomed the Government ban, which it hopes will protect two million ash trees which make up about a quarter of its forest.
Sophie Churchill, chief executive of the National Forest Company, said: "The threat from the disease chalara fraxinea is potentially extremely severe for UK woodlands and landscapes.
"The ash is generally a robust and workmanlike tree, growing readily and used for tool handles and firewood.
"It is a very important tree in the Midlands.
"It is unclear whether the outbreaks can be controlled, but even if they are it is an immense task to stop the risk of infection through imports and to track any new outbreaks.
"We support the Government treating this as an environmental emergency.
"I am very aware many people and businesses have planted ash trees with us and they will be concerned about the survival of those trees.
"We will do all we can to protect them but I have to say the threat of disease will never be eliminated."
The National Forest Company said it had an ash dieback scare two months ago.
The suspect tree was linked to 500 infected specimens which have since been felled at the Birstall park-and-ride site.
Samples were sent for testing and the tree in the National Forest was given the all-clear.
Carol Rowntree Jones, a spokeswoman for the National Forest Company, said the ban on imports would affect planned planting schedules.
She said between 20,000 and 25,000 ash trees might have been planted this season.
"The ash tree is one of our primary trees when it comes to planting," she said.
"We will now divert to a different mix. More oak, birch and, perhaps, cherry."
The Government ban prevents ash trees and seeds being brought into the UK.
It follows an eight-week consultation which showed strong support for the move being put in place before the main tree planting season starts, in mid-November.
Environment Secretary Owen Paterson said: "This very serious disease demands action to stop its spread."
