Forty seven posts in the BBC's factual programme department in Bristol and Birmingham are to be cut, the corporation has announced.
Producers and series producer roles, including 12 at the Natural History Unit, will be closed.
In Birmingham, the BBC wants to close producer, assistant producer and researcher posts.
A spokeswoman for the BBC said a total of 21 posts would be lost in Bristol and 26 in Birmingham.
In Bristol, there are 213 staff working for the factual department while there are 121 in Birmingham.
BBC Factual in Bristol is responsible for programmes such as DIY SOS, while Countryfile is among the shows the unit makes from Birmingham.
The Natural History Unit was founded in 1957 and is responsible for programmes such as Human Planet, Planet Earth and The Blue Planet.
In an e-mail to staff, the controller of Factual, Tom Archer, said it was "serious news" and "the next few weeks will be difficult".
He added the corporation was managing 5% year-on-year cuts and there was "continuing pressure" on budgets due to the pension deficit and frozen licence fee.
Helen Ryan from broadcasting union Bectu condemned the cuts, saying the staff involved delivered quality programmes for the BBC.
"We are devastated that such large numbers of talented staff are in danger of redundancy," she said.