The group of five or six offenders smashed through the gates of the Forest of Marston Vale Millennium Country Park in a black 4x4 vehicle in the early hours of Monday morning.
They drove around to the Barn and loaded up high value forestry equipment before speeding off again.
One of the items had only just been bought after a “very lengthy bidding and admin process”, said the charity.
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“Staff and volunteers are all saddened both by the financial loss and the time and effort it will take to rectify things until replacements have been resourced,” said a spokesman for the Marston Moretaine centre.
He added: “The centre is run by the Forest of Marston Vale, and such a huge loss is a devastating blow to the charity, which is planting trees and creating woodlands across the area.”
Police are investigating the theft, which happened at around 2am, and are appealing for witnesses or anybody with information.
It is believed the thieves may have been watching the premises or checked it out during the days leading up to the burglary.
Anybody who saw anything suspicious is asked to call 101 quoting the reference 40/27081/19.
They can also report online via www.bedfordshire.police.uk or contact Crimestoppers anonymously on 0800 555 111.
The Forest of Marston Vale is a registered charity covering the 61 sq mile area between Bedford and Milton Keynes that was formerly a brickworks site.
The land was designated as a community forest tin the early 1990s, when tree cover was a seriously low 3 per cent – a third of the national average at the time.
The charity has since planted more than 1.5million trees and its aim is to make the area a thriving place to live, work and play.
The spokesman said: “Back when the Forest began we received funding to keep things moving, but now we rely almost entirely on donations from the public and money made at the Forest Centre & Millennium Country Park – our flagship site.
“All money spent there goes towards helping us towards our vision of another five million trees.”